STARS AND GALAXIES

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

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.

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.

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)

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.

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

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.

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

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.

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”.

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.

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

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)

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 -1.44. The magnitude of the sun is -26.7

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 year @ 300,000 km/sec

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.

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

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

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

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

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.

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

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.

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

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

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

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

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