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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.
2.
3.
4.
5.
Ursa Major – The Big Bear
Ursa Minor – The Little Bear
Cassiopeia – Queen on Her Throne
Draco- The Dragon
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 Triangle
1. Vega- in Lyra the Harp
2. Altair- in Aquilla the Eagle
3. 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”
V. Kinds of Stars
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
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.
2.
3.
4.
5.
6.
7.
8.
Less luminous
Very dense, mostly carbon
Tightly packed nuclei
Remains of a red giant that ran out of fuel
1 cup full of star =20 tons or 5 elephants.
Most are red/orange/yellow
White dwarf is the exception to the color
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 waves
C. 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.
2.
3.
4.
5.
6.
7.
Nebula
Protostar
New/Stable State Star
Red Giant
Planetary Nebula
White Dwarf
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.
2.
3.
4.
5.
1st three steps are similar
Super Giant
Super Nova
Neutron Star / Pulsar
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 neutron
star 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 stars
A. The Sun is closest star to Earth
B. Takes light 8 minutes to reach Earth
C. Avg. distance:150,000,000Km = 1
AU distance from Earth to the Sun
D. 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.
2.
3.
4.
5.
Visible light
X-rays
Radio waves
Infrared waves
Ultraviolet waves
Venus & Saturn by E-spectrum
Ultra violet
Ultra violet
Visible
Visible
Infrared
Infrared
Radio
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 Spectrum
2. Brightline Spectrum
3. 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
red orange yellow
green
• ROY G BIV
• All the colors of
the rainbow
• A continuous
spectrum
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 planets
2.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 fingerprint
http://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.