unit c and d.docx

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UNIT C AND D

SECTION 2.1 PATTERNS IN THE NIGHT SKY

Constellations: a region of the sky with well-defined borders, the star patterns help uslocate them

o Every point in the sky belongs to some constellationo

Stars in a constellation may appear to be close by may lie very far apart

Celestial sphere: imaginary sphere on which objects in the sky appear to reside whenobserved from Earth

o Greeks actually believed universe was a sphere b/c of lack of depth perceptiono Still allows us to map the sky as seen from Eartho North celestial pole: point directly over Earths North Poleo South celestial pole: point directly over Earths South Poleo Celestial Equator: projection of Earths equator into spaceo Ecliptic: the path the Sun follows as it appears to circle around the celestial sphere

once each year (at a 23.5 angle)

Milky Wayo Band of light circles all the way around the celestial sphereo Milky Way in sky traces the galactic planeo Can hinder us from seeing the distant universe

Local Sky: the half of the celestial sphere you see at any timeo Horizon: the boundary b/w Earth and skyo Zenith: the point directly overheado Meridian: half circle stretching from N to S through zenitho Pinpoint position by direction (along horizon) and altitude (angle)

Angular Sizeo The angle it appears to span in your field of viewo Angular distance: angle that appears to separate 2 objects in the sky

Stars Rise and Set Everything in the celestial sphere appears to circle around Earth daily Circumpolar stars: always remain above the horizon for a particular latitude Stars relatively near the south celestial pole never rise above the horizon at all All other stars have daily circles partly above/below horizon

Visible Constellations Depend on Latitude and Time of YearLatitude Variations

Latitude affects locations of horizon and zenith Altitude of celestial pole in your sky = to your latitude

Variation with Time of Year

Earth changes position in orbit around the Sun Zodiac: the constellations that would appear in the ecliptic in line with the

Sun, if we could see Sun and stars at the same time

o We can not see the zodiac because they move with the SunSECTION 2.3 THE MOON

Orbits Earth every 27 1/3 days Rises in east, sets in west, but appears to move eastward from night to night


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Phases of the Moon

Appearance and times that it rises go through a cycle Half of the moon is always illuminated by sun, but the amount we see depends on the

Moons position in orbit

Waxing: in between new and full Waning: in between full and new Crescent: a Gibbous:

Moons Synchronous Rotation

Moon rotates on its axis in same time it takes to orbit Earth, therefore we always see thesame side

Result of Earths gravityEclipses

Moons orbit is inclined to the ecliptic plane by 5 (why we dont have eclipses everymonth)

Nodes: the 2 points in each orbit where the moon crosses the ecliptic plane The phase of the moon must be full or new and must occur during one of the periods

when the nodes are aligned with the Sun and Earth

Two regions of shadowo Umbra: where sunlight is completely blocked (center)o Penumbra: sunlight is only partially blocked

Lunar Eclipse: when Earth lies directly b/w the Sun and Moon, Earths shadow falls onMoon

o Can be total or partialo Penumbral lunar eclipse if Moon passes only through penumbra

Solar Eclipse: Moon lies b/w Earth and Sun and casts its shadow on Eartho Total if seen from the Moons umbra, partial if in the penumbrao Annular: if Moon is far away, umbra wont reach Earth and there will be a ring of

Sun around the moon

Eclipsing seasons: 2 periods every year when the nodes are nearly aligned with the Sun,lasts a few weeks

Saros cycle: the period over which the basic pattern of eclipses repeats, about 18 yrs, 111/3 days

SECTION 2.4 ANCIENT MYSTERY OF THE PLANETS

Mercury-Saturn are easy to see with the naked eye Rise in E, set in W like all things in the sky

Planets usually move eastward through constellations like Sun and Moon, but sometimeshave apparent retrograde motion: appear to reverse course

o Earth orbits Sun faster than planets further out Aristarchus first proposed the Sun-centered model in 260BC but everyone rejected his

idea until 2000 yrs later

Greeks expected to see parallax a different way b/c they believed all stars were on thesame celestial sphere


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o If Earth orbited Sun, we were be closer to different stars in the sphere at differenttimes of the year, but they angular separation never changed so they didnt believe

that model

SECTION 3.2 ANCIENT GREEK SCIENCE

Greece rose as a power around 500 BC, we get much of our science from them

o They developed tradition of understanding nature without relying on thesupernatural

o Used math to give precision to their ideaso Used the power of reasoningo Created models: represent an aspect of nature that can be used to explain and

predict real phenomena

Explained properties of matter and motions of the stars, moon, and planetsExplaining Planetary Motion

Believed in geocentric model: spherical Earth at center of the universe Early Geocentric Model

o Greek science traced to Thales Thought Earth was a flat disk floating in infinite oceano Anaximander: student of Thales, suggested Earth floats in empty space

surrounded by celestial sphere

Thought Earth was cylindricalo Pythagoras: Earth is roundo Eudoxus: made a model in which Sun, Moon, and planets had their own spheres

nested w/in other spheres, reproduced many observed motions of their objects

o Aristotle: all spheres of motion were transparent and interconnected Also, gravity pulls heavy things to center of universe, which formed Earth

Ptolemy

Earth still at center, but planets moved around Earth on a small circle that turns upon alarger circleo Explains apparent retrograde motiono Based on other scientists work

Preserving Greek Knowledge

Their society was great at everything from science to politics to philosophy City of Alexandria began work on the Library shortly after Alexander the Greats death

o Worlds best research center for 700 years, ultimately destroyed Whatever survived preserved by a new center in Baghdad

o Scholars in Islam used knowledge to better understand Allah while Europe was inthe Dark Ages

o Most of the star names and constellations come from Arabic Islamic world frequently made contact with India and in turn China Accumulated knowledge spread through Byzantine Empire and to Europe when

Constantinople fell

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