1. STARS AND GALAXIES

2. 1. Light
Light is a form of electromagnetic radiation, which travels in waves
All forms of ER travel in waves
This includes radio waves, microwaves, infrared waves (heat), x-rays, and cosmic waves
These forms of energy make up the electromagnetic spectrum

3. 1. Light continued:
All forms of ER travel at the “speed of light”, which is 300,000 km/sec
Many objects, such as stars, emit many forms of ER.
ER does not require a substance to travel through like sound or water waves
ER can travel through a vacuum, such as the vacuum of space.

4. 2. Electromagnetic Spectrum
The part of the Electromagnetic Spectrum that we see is called “visible light”.
Visible light is a very small part of the ES.
When visible light is broken down by using a spectroscope, we can see the colors of the rainbow.
The colors of the visible spectrum can be represented by ROYGBIV
Each color is different from every other because each color has a different wavelength.

5. 3. Crest-top of wave Trough-bottom of wave
Wavelength-distance from trough to trough
Frequency-number of waves per time unit (waves per second)

6. 4. Spectroscope
A spectroscope can break light into many different types of spectra.
By analyzing these different types of spectra, astronomers can determine what elements make up the atmospheres of stars and planets.

7. 5. Continuous Spectrum-unbroken band of colors which shows that the source is emitting light of all visible wavelengths.

8. 6. Emission Spectrum-
An emission spectrum is a series of unevenly spaced lines of different intensity and color.
The bright lines show that the source is emitting light on only certain wavelengths.

9. 7. Absorption Spectrum
An absorption spectrum is a continuous spectrum crossed by dark lines

10. 8. Spectral Analysis
Spectral Analysis tells astronomers not only what stars are made of but also how they are moving in relation to the Earth.

11. 9. Doppler Effect
The Doppler Effect causes the pitch of a sound to change as the source approaches the listener, the Doppler effect can be detected in light also.
Since light also travels in waves, the Doppler Effect can be detected in light also.
If a star is moving away from the Earth, the light waves stretched, and then the tends to make them red in color.
If the star is moving toward the observer, the light waves are squeezed, this shortens the wavelengths, and tends to make them blue in color.
This is called the “blue shift”.

12. 10. Constellations
Patterns of familiar objects in the sky made by the stars are constellations.
There are 88 identified constellations
Some constellations are visible only during certain seasons.
A constellation visible any time during the year is circumpolar.

13. 11. Constellations Constellations appear to move across the sky
This is due to the earth’s rotation and revolution around the sun.

14. 12. Star Brightness
Individual stars appear to be of different brightness as we see them from Earth.
Apparent magnitude is a measure of how bright a star looks from Earth..
The lower a star’s magnitude number, the bright the star. (-1 is brighter than 2, for example)

15. 12. Star Brightness (Luminosity)
Some of the brightest stars we see with the unaided eye are classified as low magnitude stars.
The faintest stars that can be seen with the unaided eye are high magnitude stars
The brightest star we see is Sirius, with a magnitude of
The magnitude of the sun is -26.7

16. 13. Distances in Space
Astronomical unit-(AU) avg. distance between Earth and Sun
Jupiter is 5.2 AU from the sun
Light-year used for distances beyond the solar system
Light Year Distance light would travel in one 300,000 km/sec

17. 15. Star Mass The masses of stars are compared to the mass of our sun.
A star 5 times more massive than the Sun would have a mass of 5 solar masses.
The largest star would have a mass of about 2000 times that of the sun, the smallest is smaller than the Earth.

18. 16. Temperature & Color Stars vary greatly in temperature
The color of a star may depend on the temperature of the star
Generally, “cool” stars tend to be red, say around 3000 C.
Yellow-white stars are hotter, around 5000 C
Bluish-white stars are the hottest, up to 30,000 C

19. 17. Luminosity
The actual brightness of a star is called it’s luminosity
A star’s luminosity depends upon it’s size and temperature
A star’s distance from the Earth is not a factor in luminosity

20. 18. Absolute Magnitude
In order to compare all star’s equally, astronomers use absolute magnitude,
Absolute magnitude is a measure of the brightness of stars if all stars were the same distance from the earth

21. 19. Variable Stars Most stars shine with constant brightness
Some stars brightness change and those stars are called variable stars
Stars that change brightness when the star expands and collapses are called pulsating stars

22. 20. Star life cycles Stars go through life cycles
Star are born out of a cloud of gas/dust called a nebula.
Gravity is the force that causes the material to collect
A protostar may form if sufficient density if reached.

23. 20. Star life cycles
A protostar is like the teenage years in a star’s life cycle
Eventually, heat from friction may produce reach the level in which fusion may begin
Hydrogen converted to helium, producing large amounts of energy

25. 21. Main Sequence Stars
Stars vary greatly in size, but normally after a protostar is formed, the star reaches adulthood, and this stage is called main sequence
Stars remain in main sequence for most of their lives
Most stars we see are main sequence stars.

26. 22. Main Sequence to Red Giant
Stars similar in size to the sun will often form red giants after the main sequence
This occurs when the hydrogen stars running out and the star cannot generate enough heat any longer
Gravity causes the star to collapse, then explode into a red giant

27. 22. Red Giant to Dwarf Star
A red giant, may cool quickly forming a white dwarf.
Sometimes a white dwarf will illuminate a surrounding collection of gas/dust called a planetary nebula

28. 23. Super Red Giant
For stars much larger than the sun, a super red giant may form
Eventually, the super red giant will collapse and explode into a supernova
The supernova may then collapse into a neutron star, an incredibly dense object

29. 24. Black Holes
If the original star is 15 or more solar masses, a black hole may form
A black hole has such intense gravity, that not even light can escape

30. 25. Galaxies Galaxies are systems containing millions of stars
Our Solar System is in the Milky Way Galaxy
There are several types of galaxies, categorized by shape
There are elliptical, spiral, and irregular galaxies
Galaxies may contain extremely bright objects called quasars.
Quasars may be up to 12 billion light years away