2. So You Wanna’ Be A STAR Characteristics of Stars Stellar Evolution

3. What is a Star? A body of gases that undergo fusion to create massive amounts of energy in the form of electromagnetic radiation

4. Characteristics of Stars Astronomers look at stars through telescopes to analyze the light they emit and their relationships to other stars. This can reveal to us a star’s: Composition Color Temperature Mass

5. Composition of Stars A star is made of different elements in the form of gases. The gases in the atmosphere of a star absorb different wavelengths of light depending on which elements make up the gases. The light from a star indicates which elements make up that star.

6. The Colors of Light A prism breaks white light into a rainbow of colors called a spectrum. An instrument called a spectrograph is used to break a star’s light into a spectrum. The spectrum of a star will vary depending on which elements are present. Composition of Stars

7. There are 3 types of spectra Continuous: Where all colors are present. Continuous: Where all colors are present. Emission: Where only a few colors are present. Emission: Where only a few colors are present. Absorption: Where a few colors are missing. Absorption: Where a few colors are missing.

8. How a Continuous Spectrum is Created. If we pass white light trough a prism, it will be dispersed into a spectrum corresponding to ROYGBIV. If we pass white light trough a prism, it will be dispersed into a spectrum corresponding to ROYGBIV. There are no colors missing. That’s why we call it a continuous spectrum. There are no colors missing. That’s why we call it a continuous spectrum.

9. How an Emission Spectra is Formed. If the atoms in a gas become excited, it will emit light. If the atoms in a gas become excited, it will emit light. If we pass that light through a prism, it will be broken down into its component colors. If we pass that light through a prism, it will be broken down into its component colors. Just like the lab we’ll do today. Just like the lab we’ll do today.

10. Each Element Emits its Own Unique Spectra Hydrogen Hydrogen Helium Helium Mercury Mercury Iron Iron Nitrogen Nitrogen

11. Absorption Spectra is the Opposite of the Emission Spectra Instead of a hot gas emitting light… Instead of a hot gas emitting light… A cool gas absorbs light. A cool gas absorbs light. That is why we call it an absorption spectrum. That is why we call it an absorption spectrum.

12. This creates an Absorption spectum Where specific frequencies or colors are absorbed and do not show up Where specific frequencies or colors are absorbed and do not show up

13. Emission and Absorption The same colors emitted by a hot gaseous element… The same colors emitted by a hot gaseous element… Are absorbed by that same cool gaseous element Are absorbed by that same cool gaseous element

14. How do we know what a star is made of? A star is too hot and far away to take a sample. A star is too hot and far away to take a sample. Nothing would survive this job. Nothing would survive this job. Not even fire-proof monkeys Not even fire-proof monkeys

15. So we use absorption spectra The outer layers of the sun absorbs some light. The outer layers of the sun absorbs some light. We can determine what elements are in the outer layer by examining the spectra. We can determine what elements are in the outer layer by examining the spectra. The missing colors correspond to the gases that absorbed them. The missing colors correspond to the gases that absorbed them.

16. Composition When the spectrum of a star is studied the spectral lines act as “fingerprints.” These lines identify the elements present and thus the star’s chemical composition.

17. Color & Temperature A star’s color is an indication of its temperature A star’s color is an indication of its temperature HOT stars emit SHORT-wavelength light and appear BLUE HOT stars emit SHORT-wavelength light and appear BLUE COOL stars emit LONGER-wavelength light and appear RED COOL stars emit LONGER-wavelength light and appear RED Stars in the MIDDLE appear YELLOW, like our sun Stars in the MIDDLE appear YELLOW, like our sun

18. Color & Temperature Star Color Surface Temp. (ºC) Examples Blue Above 30,000 10 Lacertae Blue-White10,000-30,000 Rigel, Spica Blue-White7,500-10,000 Vega, Sirius Yellow-White6,000-7,500 Canopus, Procyon Yellow5,000-6,000 Sun, Capella Orange3,500-5,000 Arcturus, Aldeberon Red Less than 3,500 Betelgeuse, Antares

19. Stellar Brightness The measure of a star’s brightness is its magnitude The visibility of a star depends on its brightness and distance from the earth

20. Apparent Magnitude  The brightness of a star as it appears from Earth  Scaled from -30 to +29; the brighter the star, the smaller the number  The sun has an apparent magnitude of -26.8  The dimmest star visible with the unaided eye is +6

21. Absolute Magnitude  How bright a star actually is  Two stars with the same apparent magnitude do not usually have the same absolute magnitude because one may be much further from us than the other  To determine absolute magnitude astronomers determine how bright a star would appear if it were seen at a distance of 32.6 light years  Most stars have an absolute magnitude between - 5 and +15.  The sun has an absolute magnitude of +5

23. Measuring Distances in Space  Due to the vastness of space, normal earth based measurements like kilometers are too small for the scale of the universe. Because the distances are so great, all movement of stars and other objects in space appear to be the same (even though they are not)

24.  A light-year is the distance light travels in one year  300,000 km/s; 180,000 mi/s  About 9.5 x 10 12 or 9.5 trillion kilometers in one year  Proxima Centauri, the second closest star to Earth, is about 4.3 light-years away from the sun Light-Year

25. Parallax Parallax is the apparent shift in the position of an object when viewed from different locations. Measuring parallax enables scientists to calculate the distance between a star and the Earth.

26. Motions of Stars The Apparent Motion of Stars If you look at the night sky long enough, the stars also appear to move. The Actual Motion of Stars The apparent motion of the sun and stars in our sky is due to Earth’s rotation. But each star is also moving in space. Their actual movements, however, are difficult to see.

27. Apparent Motion of Stars

28. Actual Motion of Stars