Constellations & Stars

I. Constellations

• Group of stars that appear to form a pattern in the sky.

• 88 recognized by International Astronomy Union

A. Zodiac

• Band of 12 constellations along the ecliptic.

B. Ecliptic

• – the plane of the Earth’s orbit around the sun

• The apparent path that the sun (and planets) appear to move along against the star background.

Ecliptic

C. Circumpolar Constellations

• Can be seen all year long

• Never fully set below the horizon

• Appear to move counter clockwise around Polaris

• Caused by Earth’s Rotation

Circumpolar Constellations

Star Trails

Examples of Circumpolar Constellations

1. Ursa Major – The Big Bear2. Ursa Minor – The Little Bear3. Cassiopeia – Queen on Her Throne4. Draco- The Dragon5. Cepheus- The King

• # of stars seen as circumpolar depends on the observers latitude

• Further North the observer lives, the more stars will appear circumpolar

• Earth turns west to east

• Sky appears to turn east to west

D. Ursa Major

• Best known constellation• Common name is Big Dipper• Pointer stars- front 2 stars of the

Big Dipper which point to Polaris (North Star)

II. Seasonal Changes in Constellations

• Big Dipper – In Fall: Low over northern horizon– Spring: High overhead

• Cassiopeia – In Fall: Straight overhead– Spring: Low over northern horizon

Seasonal Change & Nightly change of the Dippers

III. Summer Constellations

• 1st 3 bright stars that rise form the Summer TriangleSummer Triangle

1. Vega- in Lyra the Harp2. Altair- in Aquilla the Eagle3. Deneb – in Cygnus the Swan

(Northern Cross)

Summer Triangle

IV. Most Famous Winter Contellation

• Orion Contains: 1. Betelgeuse (Bet el

jooz) a bright red super giant star found forming Orion’s right shoulder

2. Rigel – a blue super giant: 7th brightest star in the nighttime sky

3 Stars of Orion’s Belt

• Can be used to find 2 other constellations & a star cluster

1. Canis Major- (Big Dog) follow the line made by the 3 stars of Orion’s belt down to the left

–Sirius- the brightest star in the nighttime sky is found in Canis Major

2. Taurus (the Bull)

• Follow the line made by Orion’s belt up & to the right

• Aldebaran- Red star that is the eye of the bull is the 13th brightest in the nighttime sky

3. Pleiades Star Cluster (7 sisters)

• Follow the line made by Orion’s belt up to the right, go through Taurus to a clump of stars to the right.

• Called Subaru in Japan – means “Unite”

A. Red Giant - large red star at least 10x diameter of the sun

• Old Stars• Ex. Aldebaran• The sun will swell

into a Red Giant when it is old

V. Kinds of Stars

B. Super Giant

• Largest of all stars 100x more luminous

• Explode as a Super Nova• Can form Black Holes• Ex. Betelgeuse, Rigel, Polaris

C. Dwarf Stars 

1. Less luminous 2. Very dense, mostly carbon3. Tightly packed nuclei4. Remains of a red giant that ran out of fuel5. 1 cup full of star =20 tons or 5 elephants. 6. Most are red/orange/yellow7. White dwarf is the exception to the color8. Sun is a yellow dwarf

Size Comparison of Various Stars

VI. Variable Stars

• Change in brightness over regular periods of time

• Ex. Cepheid Variables/Pulsating Stars Binary Stars & Eclipsing Binary Stars

A. Cepheid Variables/Pulsating Stars

• Change in brightness as they expand & contract

• Unequal balance between gravity & nuclear fusion

• Ex. Polaris, Betelgeuse

B. Binary Star Systems

• Two stars of unequal brightness revolving around a center point

• Ex. Algol & its companion star in Perseus

C. Eclipsing Binary Stars

• Two close stars that appear to be a single star varying in brightness.

• The variation in brightness is due to one star moving in front of or behind the other star.

Occurs because we see the system on edge instead of from above or below

VII. Pulsars or Neutron stars

A. Discovered in 1967 (LGM)B. A distant heavenly object that emits

rapid pulses of light & radio wavesC. Formed when a Super Giant

collapses; Protons & Electrons are forced so close together that they fuse and form only neutrons 

Twinkle Twinkle Little Star

"Twinkling Stars" are due to Earth's atmosphere

VIII. Life Cycle of a Medium Mass Star

1. Nebula2. Protostar3. New/Stable State Star4. Red Giant5. Planetary Nebula6. White Dwarf7. Black Dwarf

1. Nebulae (Plural of Nebula)• Space gas seen as faint glowing

clouds • Mostly hydrogen    • Star dust is extremely small, smaller

than a particle of smoke & widely separated, with more than 300 ft. between individual particles.

• Nebulae still hinder star gazing because they absorb light which passes through them.

Types of Nebulae

• Diffuse Nebula - gases glow from stars w/in them

Ex. Nebula found in

Sagittarius

Types of Nebulae

• Dark Nebula - nebula not near a bright star 

• Ex. Horse Head Nebula in Orion

2. Protostar

• Shrinking gas balls, caused by a swirl of gas forming dense areas. 

• The gravity of the dense swirl in turn attracts nearby gases so a ball forms.

• Nuclear fusion occurs & Helium is formed from Hydrogen

• A new star is born in our galaxy every 18 days

3. Stable State Star

• Star that releases energy in enough force to counter balance gravity

• Star stops contracting• Also known as a main sequence

star• Ex. Sun

4. Planetary Nebula

• The outer layers of the Red Giant puff out more and more.

• The star loses gravitational hold on its outer layers and they get pushed away by the pressure exerted from solar winds

Planetary Nebula

5. White Dwarf

• Fuel is used up• No nuclear fusion

occurring• Remaining heat

radiates into space

IX. Life Cycle of a Massive Star

1. 1st three steps are similar 2. Super Giant 3. Super Nova4. Neutron Star / Pulsar5. Black Hole

1. Super Giant

• Rare stars, largest of all • 100x more luminous• Only stars with a lot of mass can

become super giants• Some are almost as large as our

entire solar system• Ex. Betelgeuse & Rigel

2. Super Nova • Explosion from a massive Super Giant• Outer layer blasts away at end of Life

Cycle• Emits light, heat, X-rays, & neutrinos

• Leaves behind a neutronstar or black hole

3. Neutron Star/ Pulsar

• The remains of a super nova • Very small, super-dense star which

is composed mostly of tightly-packed neutrons

• Rapidly spinning leftovers of a star • Emits energy in pulses

4. Black Hole

• Occurs when a star's remaining mass is greater than three times the mass of the Sun

• Star contracts tremendously • Incredibly dense with a gravitational

field so strong that even light cannot escape.

Life Cycle of a Massive Star

X. Distance to starsA. The Sun is closest star to Earth B. Takes light 8 minutes to reach

EarthC.Avg. distance:150,000,000Km = 1

AU distance from Earth to the SunD.Next nearest star is Proxima

Centauri 4.2 light years away; it can only be seen in the southern hemisphere

    

E. Light year

• The distance light has traveled in a year

• 9.5 x 1012 Km/yr

• Speed of light 300,000 Km /sec

XI. Physical Properties of Stars

A.Nuclear fusion supplies the energy for stars– Huge size & mass of a star means

outer layers press inward w/ tremendous pressure

– Hydrogen ignites– Star becomes a huge nuclear bomb– Hydrogen nuclei combine to form

Helium

B. Color of star depends on surface temp.

1. Blue - hottest stars Ex. Rigel in Orion; Vega in Lyra; Sirius in Canis Major

2. Yellow - medium stars ex. Sun

3. Red - coolest stars Ex. Betelgeuse in Orion, Antares the heart of Scorpio, Aldebaran in Taurus

C. Star size

-Varies, large range

Smallest can be smaller than Earth

Largest may be 600,000,000 x Earth.

D. The Sun

• is an average star

• yellow in color

• 300,000 x the mass of Earth

XII. Luminosity

• Brightness of a star• Depends on size & temperature • Hertzsprung-Russell Diagram

graphs Absolute Magnitude (or Luminosity) vs. Temperature of stars– Shows the life cycle of stars

Hertzsprung-Russell Diagram

A. Absolute Magnitude

• Measure of the amount of light it actually gives off if all stars were placed a distance of 32.6 light years away

• Lower # means brighter star

• Negative #’s are the brightest

• Ex. Sun = 4.75 Sirius = 1.4 Rigel = –7.0

Rigel’s the Brightest of the 3 listed if all were lined up next to each other.

B. Apparent Magnitude

• A measure of the amount of light received on Earth

• Stars below 0 are brightest

• Each magnitude differs by 2.5

• 1st magnitude is 100 x brighter than 6th magnitude

• Ex. Sun = – 26.8 Sirius = – 1.45 Full Moon –12 .6 Rigel = .11

• Sun is the brightest in our sky.

XIII. Galaxies

• Systems containing millions or billions of stars, gas, & dust held together by gravity      Ex. Milky Way

• There are great distances between galaxies

• The Milky Way belongs to a group or cluster of galaxies called the local group

Spiral Galaxy Like the Milky Way

Three major classes of galaxies:

1. Elliptical - shaped like large ovals or football shape

2. Spiral - pinwheel shaped; our sun is on a spiral arm of the Milky Way

3. Irregular - many different shapes that aren't like the other two

XIV. Quasar• Quasi stellar radio source• Galaxies, very far away, with bright

centers• Thought to have a super massive black

hole at center• Most luminous objects known to man

XV. Electromagnetic Spectrum

• The arrangement of electromagnetic radiation from Radio waves to Gamma waves

Stars Emit:

1. Visible light 2. X-rays 3. Radio waves4. Infrared waves5. Ultraviolet waves

Venus & Saturn by E-spectrum

Ultra violet Visible Infrared Radio

Ultra violet Visible Infrared Radio

X-ray & Ultra Violet Image of Sun

Visible, Infrared & Radio Images of Sun

A. Electromagnetic waves:

• Differ in wavelength & frequency  

• All electromagnetic waves travel at the speed of light; 300,000 km/sec

Parts of a Wave

• a has a longer wavelength (distance from one crest to another) but lower frequency ( # of waves that pass by a point in a second)

• b has a shorter wavelength but a higher frequency

B. Spectroscope

• Instrument that separates light into its colors.

• Contains: Prism at one end Slit at opposite end

which lines up with the light source

C. 3 Types of Spectra

1. Continuous Spectrum2. Brightline Spectrum3. Darkline Spectrum

How Spectra are Produced

1. Continuous Spectrum

• Produced by a glowing solid

• Example a Tungsten white light bulb, & white sunlight.

Continuous Spectrum Cont’

• Continuous set of emission lines forming an unbroken band of colors from red to violet.

• Shows the source is sending out light of all visible wavelengths.   

Visible Spectrum

• ROY G BIV

• All the colors of the rainbow

• A continuous spectrum

red  orange yellow green blue indigo       violet

2. Dark-Line Spectrum / Absorption Spectrum

• Produced when a cooler gas lies between the observer and an object emitting a continuous spectrum

• Example:1. The atmosphere of planets2.Outer layers of a star

Absorption Spectrum Cont’

• The cooler gas absorbs specific wavelengths of radiation passing through it.

• This spectrum appears as a continuous spectrum of all colors with a number of gaps or dark lines throughout it.

3. Bright-Line Spectrum / Emission Spectrum• Produced by a glowing gas which

radiates energy at specific wavelengths characteristic of the element or elements composing the gas

• Example Neon signs, black lights, LED’s

Emission Spectrum Cont’

• This spectrum consists of a number of bright lines against a dark background.

• Each elements has its own distinctive spectra much like a fingerprinthttp://jersey.uoregon.edu/vlab/elements/Elements.html

XVI. The Doppler Effect

• as sound approaches the wavelength is compressed so the pitch is higher

• as sound leaves the wavelength is stretched out so the pitch is lower

• The same thing happens with light 

Doppler Effect

http://hea-www.harvard.edu/~efortin/thesis/html/Doppler.shtml

Red Shift

• If a star is moving away from Earth there is a red shift, of its line spectra; if the star is moving toward the Earth there is a blue shift of its line spectra  

Red Shift• Red shift is evidence the universe is

expanding.