kamus astronomi

7/16/2019 kamus astronomi

http://slidepdf.com/reader/full/kamus-astronomi-568bd42541c2c 1/38

A

Aberasi kromatis: cacat pada lensa yang mengakibatkan berkas cahaya untuk panjang gelombang yang berbeda

dibiaskan dengan sudut yang berbeda. Cacat ini dapat diatasi dengan memberikan lensa tambahan.

Aberasi sferis: cacat pada cermin berbentuk kulit bola yang mengakibatkan perbedaan sudut pantul antara berkas cahaya yang jatuh di titik yang dekat dari sumbu cermin dengan berkas cahaya yang jatuh di titik yang

jauh dari sumbu cermin (misalnya di tepi cermin).

Albedo: perbandingan antara intensitas cahaya yang diterima permukaan planet dari Matahari dengan yang

dipantulkan kembali. Bulan memiliki albedo 0!!" dan Bumi 0"#$.

Almanak: katalog yang berisikan jad%al fenomena benda langit seperti kapan Matahari Bulan dan planet&

planet terbit dan terbenam.

Altitud: salah satu besaran dalam sistem koordinat alt&a'imuth. Artinya adalah ketinggian sebuah benda langit

yang dihitung dari horison ke arah kutub&kutub langit. ilainya dari &0* hingga 0*.

Apfokus: jarak terjauh sebuah benda terhadap titik fokus elips orbitnya. Misalnya jarak terjauh Bumi dari

Matahari disebut dengan aphelion. +alam sistem Bulan , Bumi namanya apogee. +alam sistem bintang gandanamanya apastron. Bumi berada di aphelion saat bulan -uli.

Asensiorekta: salah satu besaran dalam koordinat ekuatorial yang mendefinisikan jarak antara titik gamma

dengan titik potong proyeksi benda langit dari kutub ke ekuator langit. Asensiorekta dihitung sepanjang ekuator

langit dari 0 , / jam berla%anan gerak harian bintang.

Asterisme: kumpulan bintang di langit yang membentuk pola tertentu. ebuah asterisme bisa saja merupakan

bagian dari sebuah rasi (misalnya bintang tujuh di rasi 1rsa Major dan 1rsa Minor) atau gabungan dari beberapa bintang di berbagai rasi (misalnya segitiga musim panas yang terdiri dari bintang 2ega +eneb dan

Altair).

Asteroid: benda kecil di tata surya yang sangat banyak terdapat di antara orbit Mars dan -upiter. elain itu ada

juga 3A ear 3arth Asteroid atau asteroid di dekat Bumi.

Astrometri: cabang ilmu dalam astronomi yang mempelajari penentuan posisi objek langit. Contohnya

penentuan orbit bintang ganda asteroid dan gerak diri bintang.

Astrofisika: cabang ilmu dalam astronomi yang mempelajari proses fisika yang terjadi di dalam objek langit.

eperti reaksi nuklir di dalam inti bintang dan proses hantaran energi dari inti bintang hingga ke atmosfernya.

Aurora: cahaya yang timbul di lapisan ionosfer akibat interaksi antara partikel bermuatan yang berasal dari

angin Matahari dengan medan magnet planet. +i Bumi aurora ada macam yaitu aurora Borealis (terlihat dariBumi belahan utara) dan aurora Australis (terlihat dari Bumi belahan selatan).

Autumnal 34uino5: saat Matahari berada tepat di ekuator langit pada sekitar tanggal " eptember setiap

tahunnya. 6ada saat itu ka%asan Bumi yang ada di utara khatulisti%a mengalami musim gugur dan yang ada di

selatan mengalami musim semi.

A%an 7ort: a%an hipotetik yang terletak di bagian tepi tata surya kita dan berisikan batuan beku yang menjadi

sumber komet. -araknya sekitar 80.000 A dari Matahari.



B

Benda 9itam (Black Body): benda hipotetis yang menyerap semua energi yang diterimanya. Benda ini dapat

didekati dengan membuat eksperimen berikut: sebuah benda berongga yang diberi lubang kecil dipanaskan.

Apabila kita amati lubang yang ada di benda tersebut maka sifat pancaran energinya mendekati sifat bendahitam.

Bimasakti: galaksi yang kita tinggali. +alam bahasa nggris galaksi ini disebut Milky%ay.

Binokular: alat bantu optik yang terdiri dari sepasang sistem lensa yang lebih dikenal dengan istilah kekeran.

Binokuler ini membentuk bayangan tegak sehingga lebih sering digunakan sebagai teropong medan;Bumi

daripada teropong langit.

Bintang: benda langit yang menghasilkan dan memancarkan energi;cahayanya sendiri.

Bola langit: bola khayal yang digunakan untuk memetakan seluruh benda langit. Bola ini merupakan perluasan

dari bola Bumi dan memiliki unsur&unsur yang mirip seperti yang dimiliki Bumi yaitu kutub utara dan selatan

langit serta ekuator langit.

Bolide: bola api yang mengeluarkan suara bergemuruh yang timbul ketika meteor melintas di udara.

Bulan: secara umum berarti satelit alami sebuah planet. ecara khusus berarti nama satelit milik Bumi. elain

itu juga memiliki arti penanda %aktu yang berisikan sekitar "0 hari dalam penanggalan;sistem kalender.

Bulge: bagian pusat dari sebuah galaksi spiral yang menonjol berbentuk spheroid yang ukuran tiga sumbunya

berbeda.

Bujur: salah satu komponen penentu koordinat dalam sistem koordinat Bumi horison ekliptika dan galaktik.

<aris bujur selalu menghubungkan kutub utara dan kutub selatan sistem koordinatnya. Biasanya memiliki nilai

0* , "#0*.

C

Centaurus: rasi berbentuk setengah manusia dan setengah kuda yang berada di belahan langit selatan. =asi ini berada sangat dekat dengan rasi Cru5. +ua kakinya dua bintang paling terang di rasi ini yaitu bintang Alfa dan

Beta Centauri menunjuk rasi Cru5 di sebelah baratnya.

Cepheid: nama turunan dari rasi Cepheus. ama rasi ini terkenal karena bintang >ariabel Cepheid yang menjadi

salah satu andalan dalam menentukan jarak galaksi yang jauh. Bintang >ariabel ini memiliki keteraturan dan

hubungan antara luminositas dengan periode >ariabilitasnya.

Ceres: nama sebuah planet katai yang terletak di sabuk asteroid (antara Mars dan -upiter). A%alnya Ceresdikelompokkan sebagai asteroid. amun berubah menjadi planet katai sejak Agustus 00#.

Cru5: rasi berbentuk salib;layang&layang yang berada di belahan langit selatan. =asi ini menjadi salah satu

penunjuk arah selatan yang cukup akurat. =asi ini dapat diamati setelah Matahari terbenam pada bulan Maret

hingga eptember.

+



+eklinasi: salah satu besaran dalam koordinat ekuatorial yang mendefinisikan jarak antara ekuator langit ke

benda langit. ilainya adalah dari &0* hingga 0*.

+iagram garpu tala: diagram yang menunjukkan pengelompokan galaksi berdasarkan bentuknya. +iagram ini

dibuat oleh 3d%in 9ubble.

+iagram 9=: diagram 9ert'sprung&=ussel yaitu diagram yang menunjukkan sebaran bintang berdasarkan

luminositas dan temperaturnya.

3

3fek +oppler: perubahan panjang gelombang suatu sumber pemancar gelombang yang dideteksi apabila

sumber tersebut bergerak relatif terhadap pengamat. 6ada pengamatan spektrum bintang;galaksi yang bergerak

kita akan melihat pergeseran panjang gelombang ke arah merah jika benda itu menjauhi kita dan pergeseran ke

arah biru jika benda itu mendekati kita.

3kuator langit: garis imajiner yang membagi langit menjadi dua bagian sama besar yaitu belahan langit utara

dan selatan. <aris ini merupakan perluasan dari garis ekuator;khatulisti%a hingga memotong bola langit.

3kliptika: bidang orbit Bumi mengelilingi Matahari. Bidang ini membentuk sudut sebesar "8* dengan ekuator langit. +apat juga dikatakan sebagai lintasan semu Matahari selama satu tahun di langit.

3lips: suatu kur>a tertutup yang memiliki dua buah titik pusat (disebut titik fokus). ?ur>a semacam ini dapat

dihasilkan dari mengiris sebuah kerucut dengan sudut irisan antara 0 hingga sudut kemiringan sisi kerucut.

?elonjongan sebuah elips dinyatakan dengan nilai eksentrisitas antara 0 dan !. 3ksentrisitas 0 akan

memberikan lingkaran ! berarti parabola dan lebih dari ! berarti hiperbola.

3longasi: sudut yang dibentuk antara Matahari Bumi dan planet.

34uino5: berarti panjang siang yang sama dengan panjang malam. @erjadi kali dalam setahun yaitu di sekitar

tanggal ! Maret dan " eptember.

luks bintang: jumlah energi yang dipancarkan satu satuan luas permukaan bintang ke segala arah.

otometri: teknik dalam astronomi yang khusus mempelajari intensitas pancaran elektromagnetik dari benda

langit.

otosfer: bagian dari Matahari yang memancarkan cahaya.

usi (reaksi): reaksi penggabungan atom&atom. +i pusat bintang seperti Matahari reaksi yang terjadi adalah

pembentukan 9elium dari 9idrogen.

<

<alaksi: kumpulan terbesar bintang&bintang di alam semesta. Memiliki bentuk dan ukuran yang bermacam&

macam seperti spiral elips dan tak beraturan. <alaksi Bimasakti (Milky ay <ala5y) berbentuk spiral.

<eosentrisme: paham yang menyatakan bah%a tata surya (alam semesta) berpusat pada Bumi dan semua bendalangit bergerak mengelilingi Bumi.



<erak harian: gerak benda langit dalam sehari terbit dan terbenam dari timur ke barat.

<erak tahunan: gerak Matahari dalam setahun yang berpindah&pindah rasi dari barat ke timur.

<erhana: peristi%a tertutupnya sebuah objek karena adanya objek yang melintas di depannya. ?edua objekyang terlibat dalam gerhana ini memiliki ukuran yang hampir sama jika diamati dari Bumi. Contohnya gerhana

Matahari dan gerhana Bulan.

<ra>itasi: gaya tarik menarik yang timbul antara benda bermassa atau lebih yang memiliki jarak tertentu.

<rup okal (ocal <roup): kelompok kecil galaksi di sekitar <alaksi Bimasakti. Beranggotakan sekitar "0

galaksi kelompok galaksi ini hanya beranggotakan sedikit galaksi yang berukuran besar di antaranya adalah

Bimasakti Andromeda A%an Magellan Besar dan A%an Magellan ?ecil.

<ugus bintang (star cluster): sekelompok bintang&bintang yang berdekatan karena dilahirkan pada daerah yang

sama. @erdapat dua jenis gugus bintang yaitu gugus terbuka dan gugus bola.

<ugus terbuka;galaktik (open cluster ): gugus bintang dengan bintang anggota berjumlah kurang dari !00

bintang. =uang antar bintang terlihat renggang

<ugus bola (globular cluster): gugus bintang dengan bintang anggota berjumlah hingga jutaan bintang. =uang

antar bintang terlihat rapat.

9

9alo galaksi: komponen terbesar dari sebuah galaksi spiral. +iperkirakan bahkan membentang lebih jauh dari

batas terjauh piringan yang bisa dilihat.

9eliosentrisme: paham yang menyatakan bah%a tata surya (alam semesta) berpusat pada Matahari dan semua

benda langit mengelilingi Matahari.

9orison: garis khayal yang membatasi %ilayah langit yang dapat diamati dengan permukaan Bumi yang dipijak

pengamat. +i laut yang luas horison mempertemukan laut dengan langit.

9ujan meteor: peristi%a terlihatnya puluhan hingga ratusan meteor dalam semalam. 9ujan meteor selalu terjadi

di tanggal yang sama setiap tahun. Batuan yang menjadi asal meteor biasanya berasal dari serpihan debu komet.

nklinasi: sudut yang terbentuk akibat dua bidang yang tidak terletak berhimpit tetapi berpotongan. nklinasi

ekliptika dengan ekuator langit adalah "8* inklinasi orbit Bulan dengan ekliptika adalah 8* .

--upiter: nama salah satu planet di tata surya kita.

?

?atai putih: salah satu tahapan akhir dari e>olusi bintang yang terjadi ketika bintang menghembuskan

selubungnya setelah menjadi planetary nebula dan hanya menyisakan bagian intinya saja. Matahari diyakini

akan menjadi sebuah bintang katai putih.



?omet: benda kecil di tata surya yang terlihat memiliki ekor ketika melintas di dekat Matahari. ?arena orbitnya

yang sangat eksentrik komet lebih sering diamati ketika berada di dekat Matahari saja. Contoh: komet 9alley

yang mendekati Matahari setiap $# tahun sekali.

?onjungsi: konfigurasi yang terbentuk ketika planet , Matahari , Bumi berada pada satu garis lurus. 1ntuk planet dalam formasi seperti itu disebut dengan konjungsi superior. edangkan konfigurasi Matahari , planet ,

Bumi disebut konjungsi inferior. udut elongasi planet saat konjungsi adalah 0* .

?onstelasi: rasi.

?orona: bagian luar Matahari yang sangat panas dan hanya dapat diamati ketika terjadi gerhana Matahari total.

?osmologi: cabang ilmu astronomi yang mempelajari sejarah e>olusi dan perkembangan alam semesta.

?uadratur (timur dan barat): konfigurasi yang terbentuk ketika elongasi planet luar adalah 0* .

?ulminasi: melintasnya sebuah benda langit di garis yang menghubungkan titik utara dan selatan. ?ulminasi

terdiri atas jenis kulminasi atas yaitu ketika benda langit melintasi garis yang menghubungkan titik utara

'enith dan titik selatan (berada di atas horison) dan kulminasi ba%ah yaitu ketika benda langit melintasi garisyang menghubungkan titik utara nadir dan titik selatan (berada di ba%ah horison).

eonid: salah satu nama hujan meteor yang terkenal karena jumlah meteornya sangat banyak dan spektakuler.

+iambil dari nama rasi eo yang menjadi titik radian;titik tempat meteor&meteor yang terjadi Dberasal.E

ubanghitam: bentuk akhir dari e>olusi bintang bermassa sangat besar. ubanghitam baru terbentuk apabila

bintang tersebut mengalami superno>a. etelah itu massa bintang yang tersisa begitu besar tetapi radiusnyasangat kecil sehingga gaya gra>itasi di permukaan sangat besar bahkan cahay tidak dapat lolos dari tarikan

gra>itasinya. Akibatnya bintang runtuh pada dirinya sendiri.

uminositas: jumlah energi per detik yang dipancarkan seluruh permukaan bintang ke segala arah. Besarnya

bergantung pada kuadrat jejari bintang dan pangkat empat temperaturnya.

M

Magnitudo: satuan yang digunakan untuk menyatakan kecerlangan suatu bintang;benda langit.

Meridian: garis khayal yang menghubungkan kutub utara langit dan kutub selatan langit dan memisahkan

belahan langit sebelah timur dengan langit barat. 6eristi%a saat objek langit melintasi meridian dari timur ke

barat disebut juga transit.

Messier: nama katalog untuk !!0 benda&benda langit yang menarik berisi nebula gugus bintang dan galaksi. ama Messier diambil dari nama penemunya Charles Messier (!$"0&!F!$) seorang astronom 6rancis.

Meteor: kilatan cahaya di langit yang diakibatkan oleh masuknya benda asing ke Bumi. Benda tersebut akan

bergesekan dengan partikel di atmosfer Bumi sehingga memanas dan memijar. Benda ini bisa saja habis

terbakar atau terus melaju hingga menumbuk permukaan Bumi.

Meteorit: meteor yang tidak habis terbakar di atmosfer dan menumbuk permukaan Bumi.



Meteoroid: benda yang ukurannya lebih kecil dari asteroid dan lebih besar dari atom yang terdapat di ruang

angkasa dan menjadi benda yang menimbulkan meteor.

Mounting: sistem penyokong suatu teleskop yang menghungkan teleskop dengan kaki&kaki penyangga (tripod

atau monopod).

ebula: sekumpulan gas dan debu yang memiliki kerapatan rendah. +apat merupakan materi pembentuk bintang atau sebaliknya merupakan sisa ledakan bintang (superno>a).

(Bintang) eutron: sisa superno>a (hasil ledakan bintang bermassa besar) yang membentuk bintang yang

sedemikian padat sehingga hanya berisikan neutron saja.

e% <eneral Catalogue (<C): katalog yang berisikan daftar nebula gugus bintang dan galaksi. -umlah

objeknya mencapai $.F/0 buah.

7

7kultasi: peristi%a tertutupnya sebuah benda langit oleh benda langit lainnya yang lebih besar. Contohnya

okultasi bintang oleh Bulan atau planet oleh Bulan.

7posisi: konfigurasi yang terbentuk ketika Matahari , Bumi , planet berada pada satu garis lurus. udut

elongasi planet saat oposisi adalah !F0* .

7rbit: lintasan sebuah benda langit dalam mengelilingi benda langit lainnya.

7rion: rasi yang digambarkan sebagai sosok pemburu. angat terkenal dengan tiga sabuk berjejer yang disebut

sabuk 7rion. =asi ini dapat diamati setelah Matahari terbenam pada bulan +esember hingga Mei.

6

6aralaks: perbedaan pandangan akibat melihat sebuah benda dari tempat yang berbeda. Contoh sederhananya

adalah melihatsebuah pensil yang digenggam di tangan sejauh "0 cm dari mata secara bergantian dengan hanya

satu mata kanan dan kiri saja. 6ensil tersebut akan terlihat berpindah relatif terhadap benda di belakangnya.

6arsek (parsec pc): jarak objek yang memiliki paralaks sebesar ! detik busur yaitu sebesar 0##8 A atau

".# tahun cahaya.

6enumbra: bayangan sebuah benda (Bulan atau Bumi) yang tidak terlalu pekat. ?etika gerhana Matahari

terjadi %ilayah di Bumi yang terkena penumbra Bulan akan mengalami gerhana Matahari sebagian. edangkan

saat gerhana Bulan penumbra kecerlangan Bulan purnama hanya akan berkurang sedikit dan sangat sulit

dideteksi mata telanjang.

6erifokus: jarak terdekat dari titik fokus untuk orbit elips. Apabila Matahari yang berada di titik fokus disebut

dengan perihelion bila bintang yang di titik fokus sebutannya adalah periastron. Bumi berada di titik perihelion

pada bulan -anuari

6olusi Cahaya: polusi karena cahaya buatan manusia justru membuat langit malam menjadi terang. 9al ini

sangat mengganggu pengamatan astronomi karena informasi dari langit datang dalam bentuk cahaya sehingga jika lingkungan sekitar terlalu terang oleh cahaya lampu penduduk;jalan maka benda langit akan semakin sulit

dilihat.



6hobos: salah satu satelit;bulan milik planet Mars.

6lanetary ebula: bentuk lanjutan e>olusi bintang bermassa kecil setelah tahap raksasa merah. Bintang akan

melontarkan selubungnya dan hanya menyisakan inti bintang menjadi katai putih. Matahari nanti akan menjadiseperti ini.

6luto: nama benda di tata surya yang sempat digolongkan sebagai planet sebelum tahun 00#. ?arena bentukorbitnya 6luto bisa menjadi lebih jauh daripada eptunus atau lebih dekat.

6ulsar: pulsating radio source. umber pemancar energi radio yang pancarannya berubah&ubah secara periodik.

Asalnya adalah bintang neutron yang berputar;rotasi dengan cepat.

G

Guasar: 4uasi stellar object. 7bjek yang tampak seperti bintang (sumber cahaya titik) namun berjarak sangat

jauh dan mengindikasikan bah%a objek ini berada di luar <alaksi. +iketahui sebagai galaksi yang memiliki

bagian inti yang aktif (Acti>e <alactic uclei).

= =asi: kumpulan bintang yang tampak berdekatan di langit dan membentuk benda khayal bila dibuat garis yang

menghubungkan bintang&bintangnya.

=eflektor: jenis teleskop yang menggunakan cermin dalam sistem optiknya.

=efraktor: jenis teleskop yang menggunakan lensa dalam sistem optiknya.

=e>olusi: gerak benda langit mengitari pusat massa sistemnya. Misalnya gerak planet&planet di tata suryamengelilingi Matahari gerak Bulan mengelilingi Bumi dan gerak

=otasi: gerak benda langit berputar pada porosnya.

abuk 2an Allen: daerah di ruang angkasa dekat Bumi yang berbentuk donat yang berisikan partikel bermuatan

atuan Astronomi A (Astronomy 1nit A1): jarak rata&rata Bumi , Matahari sebesar !/.# juta km atau

disederhanakan menjadi !80 juta km. 6enggunaan jarak ini terbatas pada lingkup tata surya.

uperno>a: peristi%a meledaknya bintang yang menjadi tahapan akhir e>olusi bintang bermassa besar.

@

@ahun Cahaya (light year ly): jarak yang ditempuh cahaya dalam %aktu ! tahun. ?alikan kecepatan tempuhcahaya ("00.000 km;dt) dengan jumlah detik dalam setahun. 9asilnya adalah /# 5 !0H!/ km atau #"/ A1.

-arak Matahari , Bumi adalah F menit cahaya.

@ata surya: sistem banyak benda yang bercirikan adanya sebuah benda dominan berupa bintang yang dikelilingi

benda&benda lainnya yang lebih kecil. 9ingga kini telah banyak ditemukan sistem tata surya di bintang lain

selain tata surya yang kita tinggali (Matahari dan F planetnya).



@eleskop: piranti optik astronomi yang membantu mata untuk mengamati benda&benda langit yang redup.

istem kerja utamanya adalah mengumpulkan cahaya.

@ransit: peristi%a melintasnya sebuah benda langit di meridian (disebut juga kulminasi atas). Arti lainnya

adalah peristi%a melintasnya planet Merkurius atau 2enus di depan piringan Matahari ketika diamati dari Bumi.

@rojan: kelompok asteroid yang berada di lintasan;orbit -upiter berjarak sudut #0* di depan dan belakang

-upiter. +engan demikian asteroid ini mengorbit Matahari bersama&sama -upiter dan tidak akan pernahmenumbuk -upiter.

1

1ltraungu: suatu daerah energi dengan panjang gelombang yang pendek dan energi tinggi.

2

2ernal e4uino5: suatu %aktu di kala Matahari berada tepat di titik perpotongan antara ekliptika dengan ekuator

sehingga pada saat itu panjang siang dan malam di Bumi di semua tempat adalah sama. @erjadi pada tanggal !

Maret. Bisa disebut juga sebagai e4uino5 a%al.

&2irginis: nama bintang >ariabel yang terletak di rasi 2irgo

I

I&ray: sinar I. 6ancaran elektromagnetik dengan energi tinggi.

J

Jerkes: nama sistem klasifikasi bintang berdasarkan luminositas.

K

Kenith: titik di langit yang berada tepat di atas kepala. a%annya adalah adir.

Kodiak: kelompok rasi yang dile%ati ekliptika (Matahari) sepanjang tahun. Ada ! rasi dalam 'odiak yang

dikaitkan dengan astrologi.



A

Absolute Magnitude

a scale for measuring the actual brightness of a celestial object %ithout accounting for the distance of the object.

Absolute magnitude measures ho% bright an object %ould appear if it %ere e5actly !0 parsecs (about "" lightyears) a%ay from 3arth. 7n this scale the un has an absolute magnitude of L/.F %hile it has an apparent

magnitude of &#.$ because it is so close.

Absolute Kero

the temperature at %hich the motion of all atoms and molecules stops and no heat is gi>en off. Absolute 'ero is

reached at 0 degrees ?el>in or &$".!# degrees Celsius.

Accretion

process of particles sticking together to form larger bodies for e5ample solar nebular dust accreted to form

chondrules and planetesimals accreted to form planets.

Achondrite

a stony meteorite representing differentiated planetary material.

Albedo eature

a dark or light marking on the surface of an object that may or may not be a geological or topographical feature.

Albedo is the measure of the reflecti>ity of a planet measured on a scale from 'ero to one. An albedo of 'ero

describes a planet that absorbs all the light it recei>es. A planet %ith an albedo of one reflects all the light that

shines on it.

Alpha Centauri

the closest bright star to our solar system.

Altitude

angle in degrees abo>e the hori'on.

Angstrom

abbre>iated N. A unit of length e4ual to !0&F cm (one&hundredth of a millionth of a centimeter). An Angstrom ison the order of the si'e of an atom.

Antimatter matter consisting of particles %ith charges opposite that of ordinary matter. n antimatter protons ha>e a

negati>e charge %hile electrons ha>e a positi>e charge.

Antipodal point

the point that is directly on the opposite side of the planet e.g. the 3arthOs north pole is antipodal to its south pole.

Apastron

the point of greatest separation of t%o stars such as in a binary star system.

Aperturethe si'e of the opening through %hich light passes in an optical instrument such as a camera or telescope. A

higher number represents a smaller opening %hile a lo%er number represents a larger opening.



Aphelion

the point in its orbit %here a planet is farthest from the un.

Apoapsisthe point in orbit farthest from the planet.

Apogeethe point in orbit farthest from the 3arth.

Apparent Magnitude

the apparent brightness of an object in the sky as it appears to an obser>er on 3arth. Bright objects ha>e a lo%

apparent magnitude %hile dim objects %ill ha>e a higher apparent magnitude.

Arc econd

abbre>iated arcsec. A unit of angular measure in %hich there are #0 arc seconds in ! arc minute and therefore

"#00 arc seconds in ! arc degree. @here are 0##8 arcseconds per radian. 7ne arc second is e4ual to about

$8 km on the un.

Arc +egree

a unit of angular measure in %hich there are "#0 arc degrees in a full circle.

Arc Minute

one !;#0 of a degree.

Asteroid

a small planetary body in orbit around the un larger than a meteoroid but smaller than a planet. Most asteroidscan be found in a belt bet%een the orbits of Mars and -upiter. @he orbits of some asteroids take them close to

the un %hich also takes them across the paths of the planets.

Astrochemistry

the branch of science that e5plores the chemical interactions bet%een dust and gas interspersed bet%een the

stars.

Astronomical unit (A1)

the a>erage distance from the 3arth to the un ! A1 is !/8$F$0 kilometers (#0!!# miles).

Atmosphere

one atmosphere is !/.$ pounds per s4uare inch (!08 e%tons per s4uare meter) the a>erage atmospheric

pressure at sea le>el on 3arth. Atmosphere is also a layer of gases surrounding a planet moon or star. @he

3arthOs atmosphere is !0 miles thick and is composed mainly of nitrogen o5ygen carbon dio5ide and a fe%other trace gases.

Aurora

a glo% in a planetOs ionosphere caused by the interaction bet%een the planetOs magnetic field and charged

particles from the un.

Aurora Borealis



the orthern ights caused by the interaction bet%een the solar %ind the 3arthOs magnetic field and the upper

atmosphere a similar effect happens in the southern hemisphere %here it is kno%n as the aurora australis.

Aurora Australis

also kno%n as the southern lights this is an atmospheric phenomenon that displays a diffuse glo% in the sky inthe southern hemisphere. t is caused by charged particles from the un as they interact %ith the 3arthOs

magnetic field. ?no%n as the Aurora Borealis in the northern hemisphere.

Autumnal e4uino5

the point on the celestial sphere %here the sun crosses the celestial e4uator from north to south. @he time %hen

the sun is at the autumnal e4uino5 defines the first day of autumn. @his happens on about eptember each

year.

A>erage orbital

speed around the un: @his is a measure of ho% fast a planet mo>es through space in kilometers per hour.

A5ial inclination

a5ial inclination is the angle at %hich a planetOs a5is of rotation is tilted %ith respect to that planetOs o%n orbit.

7n 3arth as %ell as other planets this tilt is responsible for the seasons.

A5is

also kno%n as the poles this is an imaginary line through the center of rotation of an object.

A'imuth

the angular distance of an object around or parallel to the hori'on from a predefined 'ero point.

B

Bar

a unit of measure of atmospheric pressure. 7ne bar is e4ual to 0.F$ atmospheres !.0 kg;cm !00 kilopascal

and !/.8 lbs;s4uare inch.

Barycenter the center of mass of a system of bodies e.g. the center of mass of the solar system.

Basalta general term for dark&colored igneous rocks composed of minerals that are relati>ely rich in iron and

magnesium.

Big Bang

the theory that suggests that the uni>erse %as formed from a single point in space during a cataclysmice5plosion about !F billion years ago. @he force of the e5plosion accounts for the current e5pansion of the

uni>erse.

Binary tars

a system of t%o stars that re>ol>e around a common center of gra>ity.

Black 9ole



the collapsed core of a massi>e star. tars that are >ery massi>e %ill collapse under their o%n gra>ity %hen their

fuel is e5hausted. @he collapse continues until all matter is crushed out of e5istence into %hat is kno%n as a

singularity. @he gra>itational pull is so strong that not e>en light can escape.

Blueshifta shift in the lines of an objectOs spectrum to%ard the blue end. Blueshift indicates that an object is

mo>ing to%ard the obser>er. @he larger the blueshift the faster the object is mo>ing.

Bolide

an e5ploding meteorite.

C

Caldera

a large basin&shaped >olcanic depression that is more or less circular in form. Most >olcanic calderas are

produced by collapse of the roof of a magma chamber due to remo>al of magma by >oluminous eruptions or

subterranean %ithdra%al of the magma although some calderas may be formed by e5plosi>e remo>al of the

upper part of a >olcano.

Carbonaceous chondrite

a type of primiti>e chondrite %ith e>idence of nebular processes.

Celestial e4uator

the intersection of the earthOs e4uatorial plane %ith the celestial sphere.

Celestial pole

the north and south celestial poles are points on the celestial sphere %here earths a5is of rotation intersects thecelestial sphere.

Celestial sphere

an imaginary sphere centered on the earth on %hich all of the stars are imagined to be projected.

Cepheida pulsating >ariable star. @his type of star undergoes a rhythmic pulsation as indicated by its regular pattern of

changing brightness as a function of time. @he period of pulsation has been demonstrated to be directly related

to a CepheidOs intrinsic brightness making obser>ations of these stars one of the most po%erful tools fordetermining distance kno%n to modern day astronomy.

C<

centimeter&<ram&econd (abbre>iated cm&gm&sec or cm&g&s). @he system of measurement that uses these units

for distance mass and time.

Chondrite

a meteorite containing chondrules and other components produced in the solar nebula.

Chondrule

small glassy spheres commonly found in meteorites.

Chromatic aberration



an optical lens defect causing color fringes because the lens material brings different colors of light to focus at

different points.

Chromosphere

the layer of the solar atmosphere that is located abo>e the photosphere and beneath the transition region and thecorona. @he chromosphere is hotter than the photosphere but not as hot as the corona.

Circumpolar tar a star that ne>er sets but al%ays stays abo>e the hori'on. @his depends on the location of the obser>er. @he

further outh you go the fe%er stars %ill be circumpolar. 6olaris the orth tar is circumpolar in most of the

northern hemisphere.

Coma

a spherical cloud of material surrounding the head of a comet. @his material is mostly gas that the un has

caused to boil off the cometOs icy nucleus. @his gas shines both by reflected sunlight and light emitted by

e5cited molecules. A cometary coma can e5tend up to a million miles from the nucleus.

Comet

a chunk of fro'en gasses ice and rocky debris that orbits the un. A comet nucleus is about the si'e of amountain on earth. hen a comet nears the un heat >apori'es the icy material producing a cloud of gaseous

material surrounding the nucleus called a coma. As the nucleus begins to disintegrate it also produces a trail of

dust or dust tail in its orbital path and a gas or ion tail pointing a%ay from the un. Comet comas can e5tend up

to a million miles from the nucleus and comet tails can be millions of miles long. @here are thought to be

literally trillions of comets in our solar system out past eptune and 6luto but only once per decade or so does

one become near and bright enough to see easily %ithout binoculars or a telescope.

Conjunctionan e>ent that occurs %hen t%o or more celestial objects appear close close together in the sky.

Constellation

a grouping of stars that make an imaginary picture in the sky. @here are FF constellations.

Con>ection Konea layer in a star in %hich con>ection currents are the main mechanism by %hich energy is transported out%ard.

n the un a con>ection 'one e5tends from just belo% the photosphere to about se>enty percent of the solar

radius.

Con>ection

the physical up%elling of hot matter thus transporting energy from a lo%er hotter region to a higher cooler

region. A bubble of gas that is hotter than its surroundings e5pands and rises. hen it has cooled by passing on

its e5tra heat to its surroundings the bubble sinks again. Con>ection can occur %hen there is a substantialdecrease in temperature %ith height such as in the unOs con>ection 'one.

Corona

the outermost layer of the solar atmosphere. @he corona consists of a highly rarefied gas %ith a lo% density and

a temperature greater than one million degrees ?el>in. t is >isible to the naked eye during a solar eclipse.

Coronal Mass 3jections



are huge bubbles of gas threaded %ith magnetic field lines that are ejected o>er the course of se>eral

hours.@hey are often associated %ith solar flares and prominence eruptions.

Cosmic =ay

atomic nuclei (mostly protons) that are obser>ed to strike the 3arthOs atmosphere %ith e5tremely high amountsof energy.

Cosmic tringa tubelike configuration of energy that is belie>ed to ha>e e5isted in the early uni>erse. A cosmic string %ould

ha>e a thickness smaller than a trillionth of an inch but its length %ould e5tend from one end of the >isible

uni>erse to the other.

Cosmology

a branch of science that deals %ith studying the origin structure and nature of the uni>erse.

Crater

a bo%l&shaped depression formed by the impact of an asteroid or meteoroid. Also the depression around the

opening of a >olcano.

Crystalline

indicates a rock is composed of mineral crystals rather than glass. n general %hen igneous melts cool >ery fast

they form glass (like obsidian) but %hen they cool slo%er mineral crystals ha>e an opportunity to gro%.

+

+ark Matter a term used to describe matter in the uni>erse that cannot be seen but can be detected by its gra>itational effects

on other bodies.

+eclination

the angular distance of an object in the sky from the celestial e4uator.

+ensity

the amount of matter contained %ithin a gi>en >olume. +ensity is measured in grams per cubic centimeter (or

kilograms per liter). @he density of %ater is !.0 iron is $. and lead is !!.".

+ifferentiated

%hen a (partially) molten body has been di>ided into t%o or more fractions of dissimilar compositions. n the

case of the 3arth iron&nickel metal %as differentiated from silicate material to form the planetOs core.

+isk

the surface of the un or other celestial body projected against the sky.

+oppler 3ffect

the apparent change in %a>elength of sound or light emitted by an object in relation to an obser>erOs position.

An object approaching the obser>er %ill ha>e a shorter %a>elength (blue) %hile an object mo>ing a%ay %illha>e a longer (red) %a>elength. @he +oppler effect can be used to estimate an objectOs speed and direction.



+ouble tar

a grouping of t%o stars. @his grouping can be apparent %here the stars seem close together or physical such as

a binary system.

+ouble Asteroidt%o asteroids that re>ol>e around each other and are held together by the gra>ity bet%een them. Also called a

binary asteroid.

+ust grains

not the dust one finds around the house %hich is typically fine bits of fabric dirt or dead skin cells. =ather

interstellar dust grains are much smaller clumps on the order of a fraction of a micron across irregularly

shaped and composed of carbon and;or silicates. +ust is most e>ident by its absorption causing large dark

patches in regions of our Milky ay <ala5y and dark bands across other gala5ies.

3

3clipse

the total or partial blocking of one celestial body by another.

3jecta

material from beneath the surface of a body such as a moon or planet that is ejected by an impact such as a

meteor and distributed around the surface. 3jecta usually appears as a lighter color than the surrounding

surface.

3lectromagnetic pectrum

the entire range of all the >arious kinds or %a>elengths of electromagnetic radiation including (from short to

long %a>elengths) gamma rays 5&rays ultra>iolet optical (>isible) infrared and radio %a>es.

3lectromagnetic =adiation

radiation that tra>els through >acuous space at the speed of light and propagates by the interplay of oscillating

electric and magnetic fields. @his radiation has a %a>elength and a fre4uency.

3lectron lu5the rate of flo% of electrons through a reference surface. n cgs units measured in electrons s&! or simply s&!.

3lectrona negati>ely charged elementary particle that normally resides outside (but is bound to) the nucleus of an atom.

3lectron 2olt

Abbre>iated e2. A unit of energy used to describe the total energy carried by a particle or photon. @he energy

ac4uired by an electron %hen it accelerates through a potential difference of ! >olt in a >acuum. ! e2 P !.# 5!0&! erg.

3llipse

an ellipse is an o>al shape. -ohannes ?epler disco>ered that the orbits of the planets %ere elliptical in shape

rather than circular.

3lliptical <ala5y

a gala5y %hose structure shaped like an ellipse and is smooth and lacks comple5 structures such as spiral arms.



3longation

the angular distance of a planetary body from the un as seen from 3arth. A planet at greatest eastern elongation

is seen in the e>ening sky and a planet at greatest %estern elongation %ill be seen in the morning sky.

3mission nebula

a type of nebula that shines by emitting light %hen electrons recombine %ith protons to form hydrogen atoms.

@he electron fre4uently approaches the proton in steps emitting energy as light as it gets pulled in. n one of themost common QstepsQ the recombining electron emits a photon of red light. ince many atoms in the nebula do

this all at once the nebula appears red in color. @his type of nebula is created %hen energetic ultra>iolet light

from a hot star shines on a cloud of hydrogen gas stripping a%ay electrons from the atoms (ioni'ation). @he

free electrons can then begin the process of recombination.

3nergy lu5

the rate of flo% of energy through a reference surface. n cgs units measured in erg s&!. Also measured in %atts

%here ! %att P ! 5 !0$ erg s&!. lu5 density the flu5 measured per unit area is also often referred to as Qflu5Q.

3nstatite

a type of primiti>e chondrite. @hat chondrite is dominated by the silicate mineral enstatite.

3phemeris

a table of data arranged by date. 3phemeris tables are typically to list the positions of the un Moon planets

and other olar ystem objects.

34uino5

the t%o points at %hich the un crosses the celestial e4uator in its yearly path in the sky. @he e4uino5es occur

on or near March ! and eptember . @he e4uino5es signal the start of the pring and Autumn seasons.

3rg

a cgs unit of energy e4ual to %ork done by a force of ! dyne acting o>er a distance of ! cm.

!0$ (ten million) erg s&! (ergs per second) P ! %att. Also ! Calorie P /. 5 !0!0 (/ billion) ergs.

3scape 2elocitythe speed re4uired for an object to escape the gra>itational pull of a planet or other body.

3>ent 9ori'onthe in>isible boundary around a black hole past %hich nothing can escape the gra>itational pull & not e>en light.

3>ol>ed tar

a star that is near the end of its life cycle %here most of its fuel has been used up. At this point the star begins to

loose mass in the form of stellar %ind.

35tragalactic

a term that means outside of or beyond our o%n gala5y.

35traterrestrial

a term used to describe anything that does not originate on 3arth.

3yepiece



the lens at the >ie%ing end of a telescope. @he eyepiece is responsible for enlarging the image captured by the

instrument. 3yepieces are a>ailable in different po%ers yielding differing amounts of magnification.

aculae

bright patches that are >isible on the unOs surface or photosphere.

ilament

a strand of cool gas suspended o>er the photosphere by magnetic fields %hich appears dark as seen against the

disk of the un.

inder

a small %ide&field telescope attached to a larger telescope. @he finder is used to help point the larger telescope

to the desired >ie%ing location.

ireball

an e5tremely bright meteor. Also kno%n as bolides fireballs can be se>eral times brighter than the full Moon.ome can e>en be accompanied by a sonic boom.

lare (olar)

rapid release of energy from a locali'ed region on the un in the form of electromagnetic radiation energetic

particles and mass motions.

lare tar

a member of a class of stars that sho% occasional sudden unpredicted increases in light. @he total energyreleased in a flare on a flare star can be much greater that the energy released in a solar flare.

ootpoint

the intersection of magnetic loops %ith the photosphere.

ree 3lectronan electron that has broken free of itOs atomic bond and is therefore not bound to an atom.

re4uencythe number of repetitions per unit time of the oscillations of an electromagnetic %a>e (or other %a>e). @he

higher the fre4uency the greater the energy of the radiation and the smaller the %a>elength. re4uency is

measured in 9ert'.

usiona process %here nuclei collide so fast they stick together and emit a great deal of energy. n the center of most

stars hydrogen fuses together to form helium. usion is so po%erful it supports the starOs enormous mass from

collapsing in on itself and heats the star so high it glo%s as the bright object %e see today.

<



<alactic ucleus

a tight concentration of stars and gas found at the innermost regions of a gala5y. Astronomers no% belie>e that

massi>e black holes may e5ist in the center of many gala5ies.

<alactic 9alothe name gi>en to the spherical region surrounding the center or nucleus of a gala5y.

<ala5ya large system of about !00 billion stars. 7ur un is a member of the Milky ay <ala5y. @here are billions of

gala5ies in the obser>able uni>erse. 35actly %hen and ho% gala5ies formed in the 1ni>erse is a topic of current

astronomical research.

<ala5ies are found in a >ariety of si'es and shapes. 7ur o%n Milky ay gala5y is spiral in shape and contains

se>eral billion stars. ome gala5ies are so distant their light takes millions of years to reach the 3arth. <ala5ies

are classified in three main groups spirals ellipticals and irregulars.

<alilean Moons

the name gi>en to -upiterOs four largest moons o 3uropa Callisto R <anymede. @hey %ere disco>ered

independently by <alileo <alilei and imon Marius.

<amma =ay

the highest energy (shortest %a>elength) photons in the electromagnetic spectrum. <amma rays are often

defined to begin at !0 ke2 although radiation from around !0 ke2 to se>eral hundred ke2 is also referred to as

hard 5&rays.

<eomagnetic torm

a %orld%ide disturbance of the 3arthOs magnetic field associated %ith solar acti>ity.

<eosynchronous 7rbit

the orbit of a satellite that tra>els abo>e the 3arthOs e4uator from %est to east so that it has a speed matching that

of the 3arthOs rotation and remains stationary in relation to the 3arth (also called geostationary). uch an orbit

has an altitude of about "800 km ("00 miles).

<iant Molecular Cloud (<MC)massi>e clouds of gas in interstellar space composed primarily of hydrogen molecules. @hese clouds ha>e

enough mass to produce thousands of stars and are fre4uently the sites of ne% star formation.

<lobular Cluster

a tight spherical grouping of hundreds of thousands of stars. <lobular clusters are composed of older stars

and are usually found around the central regions of a gala5y.

<ranulationa pattern of small cells that can be seen on the surface of the un. @hey are caused by the con>ecti>e motions of

the hot gases inside the un.

<ra>itational ens

a concentration of matter such as a gala5y or cluster of gala5ies that bends light rays from a background object.

<ra>itational lensing results in duplicate images of distant objects.

<ra>ity



a mutual physical force of nature that causes t%o bodies to attract each other.

<reenhouse 3ffect

an increase in temperature caused %hen incoming solar radiation is passed but outgoing thermal radiation is

blocked by the atmosphere. Carbon dio5ide and %ater >apor are t%o of the major gases responsible for thiseffect.

9

9eliocentric

sun centered.

9eliopause

the point at %hich the solar %ind meets the interstellar medium or solar %ind from other stars.

9eliosphere

the space %ithin the broundary of the heliopause containing the un and solar system.

9eliumthe second lightest and second most abundant element. @he typical helium atom consists of a nucleus of t%o

protons and t%o neutrons surrounded by t%o electrons. 9elium %as first disco>ered in our un. =oughly 8

percent of our un is helium.

9emisphere

a half of the celestial sphere that is di>ided into t%o hal>es by either the hori'on the celestial e4uator or the

ecliptic.

9ert'

abbre>iated 9'. A unit of fre4uency e4ual to one cycle per second. 7ne k9' P !000 9'. 7ne M9' P !0# (one

million) 9'. 7ne <9' P !0 9'.

9 region

a region of hot gas surrounding a young star or stars that is mostly ioni'ed. @he energetic light from theseyoung stars ioni'es the e5isting gas. @his region typically appears red as it glo%s %ith the photons emitted

%hen elections recombine %ith hydrogen protons.

9ot pot

center of persistent >olcanism thought to be the surface e5pression of a rising hot plume in 3arthOs mantle.

9our Angle

the telescope based coordinate specifying the angle in the e4uatorial plane from the meridian to a planecontaining the celestial object and the north and south celestial poles.

9&= +iagram

@he Color&Magnitude +iagram is a graph upon %hich stars are plotted by spectral type and actual luminosity. t

is named for the t%o scientists =ussell and 9ert'sprung %ho first used it in !!".

9ubbleOs a%



the la% of physics that states that the farther a gala5y is from us the faster it is mo>ing a%ay from us.

9ydrogen

the lightest and most abundant element. A hydrogen atom consists of one proton and one electron. A hydrogen

nucleus is just a single proton. 9ydrogen composes about $8 percent of the un but only a tiny fraction of the3arth. 9ydrogen is the building block of the uni>erse. tars form from massi>e clouds of hydrogen gas.

9ydromagnetic a>ea %a>e in %hich both the plasma and magnetic field oscillate.

9ypergala5y

a system consisting of a spiral gala5y surrounded by se>eral d%arf %hite gala5ies often ellipticals. 7ur gala5y

and the Andromeda gala5y are e5amples of hypergala5ies.

gneous rock

a rock that %as once molten.

mpact

a collision bet%een t%o planetary bodies. n the case %hen one is much smaller than the other (like a meteoroid

colliding %ith the 3arth) a crater may be produced on the larger body.

mpact melt spherule

spherules of shock&melted rock ejected from an impact crater. Most of these objects cool rapidly in the 3arthOs

atmosphere and solidify to a glassy state. 9o%e>er some may remain molten until they splash onto the ground

or into %ater %here they are 4uenched to form solidified particles of glass.

nclination

a measure of the tilt of a planetOs orbital plane in relation to that of the 3arth.

nfrared

light that is so red humans cannot see it. A band of the electromagnetic spectrum bet%een the >isible and themicro%a>e. 6hotons of infrared light are less energetic than photons of >isible light.

nferior 6laneta planet that orbits bet%een the 3arth and the un. Mercury and 2enus are the only t%o inferior planets in our

olar ystem.

nterplanetary Magnetic ield

the magnetic field carried along %ith the solar %ind.

nterstellar Medium

the gas and dust that e5ists in open space bet%een the stars.

on

an atom that has lost or gained one or more electrons and has become electrically charged as a result.

oni'ation



the process by %hich ions are produced typically occurring by collisions %ith atoms or electrons (Qcollisional

ioni'ationQ) or by interaction %ith electromagnetic radiation (Qphotoioni'ationQ).

onosphere

the region of the 3arthOs upper atmosphere containing a small percentage of free electrons and ions produced by photoioni'ation of the constituents of the atmosphere by solar ultra>iolet radiation. @he ionosphere significantly

influences radio%a>e propagation of fre4uencies less than about "0 M9'. n 3arthOs atmosphere the ionosphere

begins atan altitude of about 8 miles and e5tends out%ard about 80.

ron Meteorite

a meteorite %hich is composed mainly of iron mi5ed %ith smaller amounts of nickel.

rregular <ala5y

a gala5y %ith no spiral structure and no symmetric shape. rregular gala5ies are usually filamentary or >ery

clumpy in shape.

sotope

one of t%o or more atoms ha>ing the same number of protons in its nucleus but a different number of neutronsand therefore a different mass.

-

-o>ian planet

any of the four outer gaseous planets: -upiter aturn 1ranus and eptune.

-ulian +ate (-+)the inter>al of time in days and fraction of a day since ! -anuary /$!" BC <reen%ich noon.

?

?el>in

a temperature scale used in sciences such as astronomy to measure e5tremely cold temperatures. @he ?el>intemperature scale is just like the Celsius scale e5cept that the free'ing point of %ater 'ero degrees Celsius is

e4ual to $" degrees ?el>in. Absolute 'ero the coldest kno%n temperature is reached at 0 degrees ?el>in or

&$".!# degrees Celsius.

?eplerOs econd a%

a ray directed from the un to a planet s%eeps out e4ual areas in e4ual times.

?eplerOs irst a%a planet orbits the un in an ellipse %ith the un at one focus.

?eplerOs @hird a%

the s4uare of the period of a planetOs orbit is proportional to the cube of that planetOs semimajor a5is the

constant of proportionality is the same for all planets.

ke2

one thousand electron >olts.



?ilometer

abbre>iated km. ! km P !000 meters P !08 cm P 0.# mile.

?iloparseca distance e4ual to !000 parsecs.

?irk%ood <apsregions in the main belt of asteroids %here fe% or no asteroids are found. @hey %ere named after the scientist

%ho first noticed them.

?uiper Belt

a large ring of icy primiti>e objects beyond the orbit of eptune. ?upier Belt objects are belie>ed to be

remnants of the original material that formed the olar ystem. ome astronomers belie>e 6luto and Charon are

?uiper Belt objects.

agrange 6ointfrench mathematician and astronomer -oseph ouis agrange sho%ed that three bodies can lie at the ape5es of

an e4uilateral triangle %hich rotates in its plane. f one of the bodies is sufficiently massi>e compared %ith the

other t%o then the triangular configuration is apparently stable. uch bodies are sometimes referred to as

@rojans. @he leading ape5 of the triangle is kno%n as the leading agrange point or / the trailing ape5 is the

trailing agrange point or 8.

la>a

molten rock that is erupted onto the surface of a planet and is hot enough to flo%.

enticular <ala5y

a disk&shaped gala5y that contains no conspicuous structure %ithin the disk. enticular gala5ies tend to look

more like elliptical gala5ies than spiral gala5ies.

ibrationan effect caused by the apparent %obble of the Moon as it orbits the 3arth. @he Moon al%ays keeps the same

side to%ard the 3arth but due to libration 8S of the MoonOs surface can be seen o>er a period of time.

ight Jear

the distance light tra>els in a year at the rate of "00000 kilometers per second (#$! million miles per hour) !

light&year is e4ui>alent to ./#08"e! km 8FF0000000000 miles or #"/0 A1.

imbthe outer edge or border of a planet or other celestial body.

ocal <roup

a small group of about t%o do'en gala5ies of %hich our o%n Milky ay gala5y is a member.

uminositythe amount of light emitted by a star.



unar 3clipse

a phenomenon that occurs %hen the Moon passes into the shado% of the 3arth. A partial lunar eclipse occurs

%hen the Moon passes into the penumbra or partial shado%. n a total lunar eclipse the Moon passes into the

3arthOs umbra or total shado%.

unar Month

the a>erage time bet%een successi>e ne% or full moons. A lunar month is e4ual to days ! hours // minutes.

Also called a synodic month.

unation

the inter>al of a complete lunar cycle bet%een one ne% Moon and the ne5t. A lunation is e4ual to days !

hours and // minutes.

M

Mare

latin %ord for Qsea.Q <alileo thought the dark featureless areas on the Moon %ere bodies of %ater e>en though

the Moon is essentially de>oid of li4uid %ater. @he term is still applied to the basalt&filled impact basins

common on the face of the Moon >isible from 3arth.

Magellanic Clouds

t%o small irregular gala5ies found just outside our o%n Milky ay gala5y. @he Magellanic clouds are >isible

in the skies of the southern hemisphere.

Magnetic ield

a field of force that is generated by electric currents. @he unOs a>erage large&scale magnetic field like that of

the 3arth e5hibits a north and a south pole linked by lines of magnetic force.

Magnetic ield ines

imaginary lines that indicate the strength and direction of a magnetic field. @he orientation of the line and an

arro% sho% the direction of the field. @he lines are dra%n closer together %here the field is stronger. Charged

particles mo>e freely along magnetic field lines but are inhibited by the magnetic force from mo>ing across

field lines.

Magnetic 6ole

either of t%o limited regions in a magnet at %hich the magnetOs field is most intense.

Magnetosphere

the area around a planet most affected by its magnetic field. @he boundary of this field is set by the solar %ind.

Magnitude@he degree of brightness of a star or other object in the sky according to a scale on %hich the brightest star has

a magnitude &!./ and the faintest >isible star has magnitude #. ometimes referred to as apparent magnitude. n

this scale each number is .8 times the brightness of the pre>ious number. @hus a star %ith a magnitude of ! is

!00 times brighter than on %ith a >isual magnitude of #.

Magma



>ery hot fluid rock. Magma is used to describe molten rock both belo% and on top of the surface of a planet

and thus is a more general term than la>a. Magma may contain solid mineral crystals %hich are suspended in

the melt.

Main Beltthe area bet%een Mars and -upiter %here most of the asteroids in our olar ystem are found.

Major 6laneta name used to describe any planet that is considerably larger and more massi>e than the 3arth and contains

large 4uantities of hydrogen and helium. -upiter and eptune are e5amples of major planets.

Mass

a measure of the total amount of material in a body defined either by the inertial properties of the body or by its

gra>itational influence on other bodies.

Matter

a %ord used to describe anything that contains mass.

Megatonan e5plosi>e force e4ual to one million metric tons of @@. @he energy released in the e5plosion of one

megaton of @@ is e4ual to /. 5 !0 ergs.

Meridian

an imaginary circle dra%n through the orth and outh poles of the celestial e4uator.

Messier Charles

%hile hunting for comets in the skies abo>e rance !Fth century astronomer Charles Messier made a list of the positions of about !00 fu''y diffuse looking objects %hich appeared at fi5ed positions in the sky. Although

these objects looked like comets Messier kne% that since they did not mo>e %ith respect to the background

stars they could not be the undisco>ered comets he %as searching for. @hese objects are no% %ell kno%n to

modern astronomers to be among the brightest and most striking gaseous nebulae star clusters and gala5ies.

7bjects on MessierOs list are still referred to by their QMessier numberQ. or e5ample the Andromeda <ala5y

the "!st object on the list is kno%n as M"!.

Metamorphic rock

a rock that has been heated and compressed so that it recrystalli'es but does not melt.

Meteor

a small particle of rock or dust that burns a%ay in the 3arthOs atmosphere. Meteors are also referred to as

shooting stars.

Meteor ho%er

an e>ent %here a large number of meteors enter the 3arthOs atmosphere from the same direction in space at

nearly the same time. Most meteor sho%ers take place %hen the 3arth passes through the debris left behind by a

comet.

Meteoritean object usually a chunk or metal or rock that sur>i>es entry through the atmosphere to reach the 3arthOs

surface. Meteors become meteorites if they reach the ground.



Me2

one million electron >olts.

Millibar a measure of atmospheric pressure e4ual to !;!000 of a bar. tandard sea&le>el pressure on 3arth is about !0!"

millibars.

Minor 6lanet

another name used to describe a large asteroid.

Molecular Cloud

an interstellar cloud of molecular hydrogen containing trace amounts of other molecules such as carbon

mono5ide and ammonia.

adir

a term used to describe a point directly underneath an object or body.

ebula

a cloud of dust and gas in space usually illuminated by one or more stars. ebulae represent the ra% material

the stars are made of.

eutrino

a fundamental particle supposedly produced in massi>e numbers by the nuclear reactions in stars they are >ery

hard to detect because the >ast majority of them pass completely through the 3arth %ithout interacting.

eutron tar

a compressed core of an e5ploded star made up almost entirely of neutrons. eutron stars ha>e a strong

gra>itational field and some emit pulses of energy along their a5is. @hese are kno%n as pulsars.

eutronan electrically neutral elementary particle. A neutron is !F" times hea>ier than an electron.

e%tonOs irst a% of Motiona body continues in its state of constant >elocity (%hich may be 'ero) unless it is acted upon by an e5ternal

force.

e%tonOs econd a% of Motion

for an unbalanced force acting on a body the acceleration produced is proportional to the force impressed theconstant of proportionality is the inertial mass of the body.

e%tonOs @hird a% of Motion

in a system %here no e5ternal forces are present e>ery action force is al%ays opposed by an e4ual and opposite

reaction.

odule

a semi&spherical fragment of rock embedded in a matri5 %ith a different composition.



o>a

a star that flares up to se>eral times its original brightness for some time before returning to its original state.

uclear usiona nuclear process %hereby se>eral small nuclei are combined to make a larger one %hose mass is slightly

smaller than the sum of the small ones. @he difference in mass is con>erted to energy by 3insteinOs famous

e4ui>alence 3Pmc. uclear fusion is the reaction that fuels the un %here hydrogen nuclei are fused to formhelium.

ucleus

the positi>ely charged core of an atom consisting of protons and neutrons (e5cept for hydrogen) around %hich

electrons orbit.

7

7blateness

a measure of flattening at the poles of a planet or other celestial body.

7bli4uity

the angle bet%een a bodyOs e4uatorial plane and orbital plane.

7cculation

the blockage of light by the inter>ention of another object a planet can occult (block) the light from a distant

star

7lda planetary surface that has been modified little since its formation typically featuring large numbers of impact

craters (compare to young).

7ort Cloud

a theoretical shell of comets that is belie>ed to e5ist at the outermost regions of our olar ystem. @he 7ort

cloud %as named after the +utch astronomer %ho first proposed it.

7pen Cluster

a collection of young stars that formed together. @hey may or may not be still bound by gra>ity. ome of theyoungest open clusters are still embedded in the gas and dust from %hich they formed.

7pposition

the position of a planet %hen it is e5actly opposite the un as seen from 3arth. A planet at opposition is at its

closest approach to the 3arth and is best suitable for obser>ing.

7rbit

the path of an object that is mo>ing around a second object or point.

7rbital 6eriod

the amount of time it takes a spacecraft or other object to tra>el once around itOs orbit.

6



6aleo'oic

a geological term denoting the time in 3arth history bet%een 8$0 and /8 million years ago.

6alimpsesta circular feature on the surface of dark icy moons such as <anymede and Callisto lacking the relief associated

%ith craters 6amlimpsests are thought to be impact craters %here the topographic relief of the crater has been

eliminated by slo% adjustment of the icy surface.

6allasite

a stony&iron meteorite in %hich nodules of oli>ine (a silicate mineral) are surrounded by a net%ork of iron&

nickel metal.

6aralla5

the apparent change in position of t%o objects >ie%ed from different locations.

6arsec

a large distance often used in astronomy. A parsec is e4ual to ".# light years.

6atera

shallo% crater scalloped comple5 edge.

6eak ring

a central uplift characteri'ed by a ring of peaks rather than a single peak peak rings are typical of larger

terrestrial craters abo>e about 80 kilometers ("0 miles) in diameter.

6enumbrathe area of partial illumination surrounding the darkest part of a shado% caused by an eclipse.

6eriapsis

the point in the orbit closest to the planet.

6erigeethe point in the orbit of the Moon or other satellite at %hich it is closest to the 3arth.

6erihelionthe point in the orbit of a planet or other body %here it is closest to the un.

6erturb

to cause a planet or satellite to de>iate from a theoretically regular orbital motion.

6hase

the apparent change in shape of the Moon and inferior planets as seen from 3arth as they mo>e in their orbits.

6lanet

a spherical ball of rock and;or gas that orbits a star. @he 3arth is a planet. 7ur solar system has nine planets.

@hese planets are in order of increasing a>erage distance from the un: Mercury 2enus 3arth Mars -upiteraturn 1ranus eptune and 6luto.



6lanetesimal

a rocky and;or icy body a fe% to se>eral tens of kilometers in si'e that %as produced in the solar nebula.

6recambrian

a geological term denoting the time in 3arth history prior to 8$0 million years ago.

6hoton

a discrete 4uantity of electromagnetic energy. hort %a>elength (high fre4uency) photons carry more energythan long %a>elength (lo% fre4uency) photons.

6hotosphere

@he >isible surface of the un the upper surface of a con>ecting layer of gases in the outer portion of the sun

%hose temperature causes it to radiate light at >isible %a>elengths sunspots and faculae are obser>ed in the

photosphere.

6lanet

a >ery large body in orbit around a star. 6lanets can be composed mainly of rock or of dense gases.

6lanetary ebulaa shell of gas surrounding a small %hite star. @he gas is usually illuminated by the star producing a

>ariety of colors and shapes.

6lanitia

a lo% plain.

6lanum

a high plain or plateau.

6lasma

plasma consists of a gas heated to sufficiently high temperatures that the atoms ioni'e. @he properties of the gas

are controlled by electromagnetic forces among constituent ions and electrons %hich results in a different typeof beha>ior. 6lasma is often considered the fourth state of matter (besides solid li4uid and gas). Most of the

matter in the 1ni>erse is in the plasma state.

6recession

the apparent shift of the celestial poles caused by a gradual %obble of the 3arthOs a5is.

6rominence

an e5plosion of hot gas that erupts from the unOs surface. olar prominences are usually associated %ithsunspot acti>ity and can cause interference %ith communications on 3arth due to their electromagnetic effects

on the atmosphere.

6roper Motion

the apparent angular motion across the sky of an object relati>e to the olar ystem.

6roton

a positi>ely charged elementary particle. A proton is !F"# times hea>ier than an electron.



6rotostar

dense regions of molecular clouds %here stars are forming.

6seudocrater a generally circular crater produced by a phreatic eruption resulting from emplacement of a la>a flo% o>er %et

ground.

6ulsar

a spinning neutron star (burnt&out star) that emits energy along its gra>itational a5is. @his energy is recei>ed as

pulses as the star rotates.

6yroclastic

pertaining to clastic (broken and fragmented) rock material formed by >olcanic e5plosion or aerial e5pulsion

from a >olcanic >ent.

6umice

a light >esicular form of >olcanic glass %ith a high silica content it is usually light in color and %ill float on

%ater.

G

Guadrature

a point in the orbit of a superior planet %here it appears at right angles to the un as seem from 3arth.

Guasar

An unusually bright object found in the remote areas of the uni>erse. Guasars release incredible amounts ofenergy and are among the oldest and farthest objects in the kno%n uni>erse. @hey may be the nuclei of ancient

acti>e gala5ies.

=

=adial 2elocitythe mo>ement of an object either to%ards or a%ay from a stationary obser>er.

=adianta point in the sky from %hich meteors in a meteor sho%er seem to originate.

=adiation

energy radiated in the form of %a>es or particles photons.

=adiation Belt

a ring&shaped region around a planet in %hich electrically charged particles (usually electrons and protons) are

trapped. @he particles follo% spiral trajectories around the direction of the magnetic field of the planet. @he

radiation belts surrounding 3arth are kno%n as the 2an Allen belts.

=adio <ala5ya gala5y that gi>es off large amounts of energy in the form of radio %a>es.



=egolith

the layer of rocky debris and dust made by metoritic impact that forms the uppermost surface of planets

satellites and asteroids.

=ed <ianta stage in the e>olution of a star %hen the fuel begins to e5haust and the star e5pands to about fifty times its

normal si'e. @he temperature cools %hich gi>es the star a reddish appearance.

=edshift

a shift in the lines of an objectOs spectrum to%ard the red end. =edshift indicates that an object is mo>ing a%ay

from the obser>er. @he larger the redshift the faster the object is mo>ing.

=eflection nebula

a type of nebula that shines by reflected light. Bright stars near reflection nebulae emit light into the region that

is reflected by the large amount of dust there. @he si'e of the dust grains causes blue light to be reflected more

efficiently than red light so these reflection nebulae fre4uently appear blue in color.

=etrograde

the rotation or orbital motion of an object in a clock%ise direction %hen >ie%ed from the north pole of theecliptic mo>ing in the opposite sense from the great majority of solar system bodies.

=hyolite

fine&grained e5trusi>e igneous rock commonly %ith phenocrysts of 4uart' and feldspar in a glassy groundmass.

=ift

a fracture or crack in a planetOs surface caused by e5tension. 7n some >olcanoes subsurface intrusions are

concentrated in certain directions this causes tension at the surface and also means that there %ill be moreeruptions in these Qrift 'ones.Q

=ift 2alley

an elongated >alley formed by the depression of a block of the planetOs crust bet%een t%o faults or groups of

faults of appro5imately parallel strike.

=ight Ascension

the amount of time that passes bet%een the rising of Aries and another celestial object. =ight ascension is one

unit of measure for locating an object in the sky.

=ima

a fissure.

=oche imitthe smallest distance from a planet or other body at %hich purely gra>itational forces can hold together a

satellite or secondary body of the same mean density as the primary. At a lesser distance the tidal forces of the

primary %ould break up the secondary.

=otation

the spin of a body about its a5is.

=upes



the term applied to scarps on planetary surfaces many scarps are thought to be the surface e5pression of faults

%ithin the crust of the planetary object.

atellite

a natural or artificial body in orbit around a planet.

emimajor a5is

one&half of the longest dimension of an ellipse.

eyfert <ala5y

a main&se4uence star %hich rotates rapidly causing a loss of matter to an e>er&e5panding shell.

hield >olcano

a >olcano in the shape of a flattened dome broad and lo% built by flo%s of >ery fluid la>a.

hock

unusually high pressures produced briefly by an impact. @hese pressures may be sufficiently high to shattermelt and >apori'e rocky material.

ilicate

a rock or mineral %hose structure is dominated by bonds of silicon and o5ygen atoms (ie. oli>ine).

idereal

relating to or concerned %ith the stars. idereal rotation is that measured %ith respect to the stars rather than

%ith respect to the un or the primary of a satellite.

idereal day

the inter>al of time bet%een t%o consecuti>e transits of the >ernal e4uino5. More intuiti>ely it is the length of

time re4uired for 3arth to make one full rotation %ith respect to the celestial sphere && appro5imately four

minutes shorter than the solar day.

idereal month

the a>erage period of re>olution of the moon around the earth in reference to a fi5ed star e4ual to $ days $

hours /" minutes in units of mean solar time.

idereal period

the period of re>olution of a planet around the un or a satellite around its primary.

ingularitythe center of a black hole %here the cur>ature of spacetime is ma5imal. At the singularity the

gra>itational tides di>erge. @heoretically no solid object can sur>i>e hitting the singularity.

olar Cycle

the appro5imately !!&year 4uasi&periodic >ariation in fre4uency or number of solar acti>e e>ents.

olar lare



a bright eruption of hot gas in the unOs photosphere. olar prominences are usually only detectable by

speciali'ed instruments but can be >isible during a total solar eclipse.

olar ebula

the disk of dust and gas of %hich the olar ystem %as belie>ed to ha>e formed about 8 billion years ago.

olar Atmosphere

the atmosphere of the un. An atmosphere is generally the outermost gaseous layers of a planet naturalsatellite or star. 7nly bodies %ith a strong gra>itational pull can retain an atmosphere. Atmosphere is used to

describe the outer layer of the un because it is relati>ely transparent at >isible %a>elengths. 6arts of the solar

atmosphere include the photosphere chromosphere and the corona.

olar 3clipse

a phenomenon that occurs %hen the 3arth passes into the shado% of the Moon. A total solar eclipse occurs

%hen the Moon is close enough to completely block the unOs light. An annular solar eclipse occurs %hen the

Moon is farther a%ay and is not able to completely block the light. @his results in a ring of light around the

Moon.

olar inda flo% of charged particles that tra>els from the un out into the olar ystem.

olstice

the time of the year %hen the un appears furthest north or south of the celestial e4uator. @he solstices mark the

beginning of the ummer and inter seasons.

outh Atlantic Anomaly

the region o>er the outh Atlantic 7cean %here the lo%er 2an Allen belt of energetic electrically charged particles is particularly close to the 3arthOs surface. @he e5cess energy in the particles presents a problem for

satellites in orbit around the 3arth.

pectral ine

a line in a spectrum due to the emission or absorption of electromagnetic radiation at a discrete %a>elength.

pectral lines result from discrete changes in the energy of an atom or molecule. +ifferent atoms or moleculescan be identified by the uni4ue se4uence of spectral lines associated %ith them.

pectrographan instrument that spreads light or other electromagnetic radiation into itOs component %a>elengths (spectrum)

recording the results photographically or electronically.

pectrometer

the instrument connected to a telescope that separates the light signals into different fre4uencies producing a spectrum.

pectroscopy

the techni4ue of obser>ing the spectra of >isible light from an object to determine its composition

temperature density and speed.



pectrum

electromagnetic radiation arranged in order of %a>elength. A rainbo% is a natural spectrum of >isible light from

the un. pectra are often punctuated %ith emission or absorption lines %hich can be e5amined to re>eal the

composition and motion of the radiating source.

picules

the range of colors produced %hen >isible light passes through a prism.

piral <ala5y

a gala5y that contains a prominent central bulge and luminous arms of gas dust and young stars that %ind

out from the central nucleus in a spiral formation. 7ur gala5y the Milky ay is a spiral gala5y.

tar Cluster

a large grouping of stars from a fe% do'en to a fe% hundred thousand that are bound together by their mutual

gra>itational attraction.

tar

a giant ball of hot gas that creates and emits its o%n radiation through nuclear fusion. tars are arranged in

>arious classes by their spectral characteristics. @he chief classes are identified by the letters 7 B A < ?M. 3ach class contains ten subdi>isions numbered from 0 to . @he classes define a temperature or color

se4uence. tars of type 7 and B are Blue&%hite and ha>e high temperatures ("8000*? ; 0000*?) A stars are

%hite temperature !0000*? and < stars are yello%ish temperature $000*? ? stars are orange and M

stars are red temperature "000*?. olf&=ayet stars are hot blue giants. @hey are e5tremely turbulent and ha>e

a temperature of 80000 *? and higher

teady tate @heory

the theory that suggests the uni>erse is e5panding but e5ists in a constant unchanging state in the large scale.@he theory states that ne% matter is being continually being created to fill the gaps left by e5pansion. @his

theory has been abandoned by most astronomers in fa>or of the big bang theory.

tellar ind

the ejection of gas from the surface of a star. Many different types of stars including our un ha>e

stellar %inds. @he stellar %ind of our un is also kno%n as the olar %ind. A starOs stellar %ind isstrongest near the end of its life %hen it has consumed most of its fuel.

tone Meteoritea meteorite %hich resembles a terrestrial rock and is composed of similar materials.

tony ron

a meteorite %hich contains regions resembling both a stone meteorite and an iron meteorite.

tratosphere

the cold region of a planetary atmosphere abo>e the con>ecting regions (the troposphere) usually %ithout

>ertical motions but sometimes e5hibiting strong hori'ontal jet streams.

ubduction

the process of one lithospheric plate descending beneath another.

unspot



a temporary disturbed area in the solar photosphere that appears dark because it is cooler than the surrounding

areas. unspots consist of concentrations of strong magnetic flu5. @hey usually occur in pairs or groups of

opposite polarity that mo>e in unison across the face of the un as it rotates.

upergiantthe stage in a starOs e>olution %here the core contracts and the star s%ells to about fi>e hundreds times its

original si'e. @he starOs temperature drops gi>ing it a red color.

uperior planets

@he planets Mars -upiter aturn 1ranus eptune and 6luto are superior planets because their orbits are

farther from the un than 3arthOs orbit.

uperior Conjunction

a conjunction that occurs %hen a superior planet passes behind the un and is on the opposite side of the un

from the 3arth.

uperno>a =emnant

an e5panding shell of gas ejected at high speeds by a superno>a e5plosion. uperno>a remnants are often

>isible as diffuse gaseous nebulae usually %ith a shell&like structure. Many resemble QbubblesQ in space.

uperno>a

the death e5plosion of a massi>e star resulting in a sharp increase in brightness follo%ed by a gradual fading.

At peak light output superno>a e5plosions can outshine a gala5y. @he outer layers of the e5ploding star are

blasted out in a radioacti>e cloud. @his e5panding cloud >isible long after the initial e5plosion fades from >ie%

forms a superno>a remnant.

uperno>ae are the most po%erful forces in the uni>erse. All of the hea>y elements %ere created in superno>a

e5plosions.

ynchronous rotation

a satelliteOs rotational period is e4ual to its orbital period this causes the same side of a satellite to al%ays face

the planet. ynchronous rotation occurs %hen a planetOs gra>ity produces a tidal bulge in its satellite. @he

gra>itational attraction and bulge acts like a tor4ue %hich slo%s do%n the satellite until it reaches a

synchronous rotation.

@

@ectonic

the deformation forces acting on a planetOs crust.

@ektite

pherule of molten rock ejected from an impact crater and then cooled rapidly to produce glass.

@elescope

an instrument used to collect large amounts of light from far a%ay objects and increase their >isibility to

the naked eye. @elescopes can also enlarge objects that are relati>ely close to the 3arth.

@erminator the di>iding line bet%een the illuminated and the unilluminated part of the moonOs or a planetOs disk.



@errestrial

a term used to describe anything originating on the planet 3arth.

@errestrial 6lanet

a name gi>en to a planet composed mainly of rock and iron similar to that of 3arth.

@hermonuclear usion

the combination of atomic nuclei at high temperatures to form more massi>e nuclei %ith the simultaneousrelease of energy. @hermonuclear fusion is the po%er source at the core of the un. Controlled thermonuclear

fusion reactors %hen successfully implemented could become an attracti>e source of po%er on the 3arth.

@erra

an e5tensi>e land mass.

@idal forces

the gra>itational pull on planetary objects from nearby planets and moons. hen the tidal forces of a planet and

se>eral moons are focused on certain moons particularly if the orbits of the >arious objects bring them into

alignment on a repeated basis the tidal forces can generate a tremendous amount of energy %ithin the moon.

@he intense >olcanic aci>ity of o is the result of the interaction of such tidal forces.

@idal heating

the frictional heating of a satelliteOs interior due to fle5ure caused by the gra>itational pull of its parent planet

and possibly neighboring satellites.

@oroidal =adius

in a solar loop structure it is the distance from the a5is of the loop to the center of the Qsemi&circleQ that the

loop forms. 9alf of the distance from one loop footpoint to the other loop footpoint. or a doughnut it is thedistance from the center of the doughnut hole to the center (circular a5is) of the pastry. ee also 6oloidal

=adius.

@ransit

the passage of a celestial body across an obser>erOs meridian also the passage of a celestial body across the disk

of a larger one.

@rojan satellites

satellites %hich orbit at the agrangian points #0* ahead of and #0* behind another satellite. or e5ample@elesto and Calypso are trojans of aturnOs satellite @ethys.

@roposphere

the lo%er regions of a planetary atmosphere %here con>ection keeps the gas mi5ed and maintains a steady

increase of temperature %ith depth. Most clouds are in the troposphere.

@uff

the general term for consolidated pyroclastic debris.

1

1ltra>iolet



electromagnetic radiation at %a>elengths shorter than the >iolet end of >isible light. @he atmosphere of the

3arth effecti>ely blocks the transmission of most ultra>iolet light %hich can be deadly to many forms of life.

@he light that is so blue humans cannot see it.

1mbrathe area of total darkness in the shado% caused by an eclipse.

1ni>ersal @ime (1@)also kno%n as <reen%ich Mean @ime this is local time on the <reen%ich meridian. 1ni>ersal time is used by

astronomers as a standard measure of time.

2

2allis

a sinuous >alley.

2astitas

%idespread lo%lands.

2an Allen Belts

radiation 'ones of charged particles that surround the 3arth. @he shape of the 2an Allen belts is determined

by the 3arthOs magnetic field.

2ariable tar

a star that fluctuates in brightness. @hese include eclipsing binaries.

2entthe opening in the crust through %hich >olcanic material erupts.

2ernal 34uino5

the point on the celestial sphere %here the sun crosses the celestial e4uator from south to north. @he time %hen

the sun is at the >ernal e4uino5 defines the first day of spring. @his happens on about March 0 each year.

2irgo Cluster

a gigantic cluster of o>er 000 gala5ies that is located mainly %ithin the constellation of 2irgo. @his

cluster is located about #0 million light years from 3arth.

2isible ight

%a>elengths of electromagnetic radiation that are >isible to the human eye.

2isual MagnitudeA scale used by astronomers to measure the brightness of a star or other celestial object. 2isual magnitude

measures only the >isible light from the object. 7n this scale bright objects ha>e a lo%er number than dim

objects.

2olcano

(!) A >ent in the planetary surface through %hich magma and associated gases and ash erupt. () @he form orstructure produced by the erupted materials.



a>elength

the distance from crest to crest or trough to trough of an electromagnetic %a>e (see electromagnetic radiation)

or other %a>e.

hite +%arf

A >ery small %hite star that is the remnant core of a star that has completed fusion in its core. @he sun %ill become a %hite d%arf. hite d%arfs are typically composed primarily of carbon ha>e about the radius of the

earth and do not significantly e>ol>e further.

hite ight

>isible light that includes all colors and therefore all >isible %a>elengths.

olf&=ayet stars

are hot blue giants. @hey are e5tremely turbulent and ha>e a temperature of 80000 *? and higher

I

I&ray Astronomy

the field of astronomy that studies celestial objects by the 5&rays they emit.

I&ray

electromagnetic radiation of a >ery short %a>elength and >ery high&energy. I&rays ha>e shorter %a>elengths

than ultra>iolet light but longer %a>elengths than cosmic rays.Because 5&rays are absorbed by the 3arthOs

atmosphere 5&ray astronomy is performed in space.

I&ray tar

a bright celestial object that gi>es off 5&rays as a major portion of its radiation.

J

Joung%hen used to describe a planetary surface QyoungQ means that the >isible features are of relati>ely recent

origin i.e. that older features ha>e been destroyed by erosion or la>a flo%s. Joung surfaces e5hibit fe% impact

craters and are typically >aried and comple5 in contrast an QoldQ surface is one that has changed relati>elylittle o>er geologic time. @he surfaces of 3arth and o are young the surfaces of Mercury and Callisto are old.

K

Kenitha point directly o>erhead from an obser>er.

Kodiac

an imaginary belt across the sky in %hich the un Moon and all of the planets can al%ays be found.

Kodiacal ighta faint cone of light that can sometimes be seen abo>e the hori'on after sunset or before sunrise. Kodiacal light

is caused by sunlight reflecting off small particles of material in the plane of the olar ystem.

kamus astronomi

Documents