Astronomy (cont.) Cosmic Measurements

1. Astronomy (cont.)Cosmic Measurements Astronomical Unit (AU) - distance from earth to the sun ~150 million kilometers (93 million miles) - used to express distances to other planets Light year – distance light travels in one year at 300,000 km/sec (186,000 miles/sec) - which equals 9.46 x 1012 km (If 1 ft. equals 1AU, then 120 miles equals 1 light year)

2. Lightyear • Therefore, a light second is 186,000 miles (300,000 kilometers). A light year is the distance that light can travel in a year, or: • 186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year • A light year is 5,865,696,000,000 miles (9,460,800,000,000 kilometers). That's a long way!

3. Properties of Stars Mass & Size → Density - smallest are smaller than Earth - largest are 2000 times bigger than our sun Temperature (color) red → cooler 5,0000 F (3,000 K) blue → hottest 40,0000 F (30,000 K)

4. Properties of Stars Composition – done by light spectrum analysis, most stars are made of hydrogen & helium (determined by temperature & composition no two are alike)

5. Properties of Stars Star Brightness luminosity – depends on size & temperature apparent magnitude – as seen from Earth: brightest are ≤ 1 faintest are ≥ 6 absolute magnitude – expresses luminosity of stars as if they were all seen 32.6 light- years from Earth (our sun = 4.8)

6. Life of the Stars: Origin • Nebula – huge cloud of gas and dust in space • Gravity causes the gas in the nebula to contract to form a Protostar (– very young star that is not hot enough to shine by nuclear fusion H2 + H2→ 2He2 ) this is electromagnetic radiant energy

7. As gravity packs matter more tightly – the protostar’s temperature rises until it reaches a temperature high enough for nuclear fusion to begin Nuclear fusion is Hydrogen fusing to form Helium…. H2 + H2 = 2He + electromagnetic radiant energy (The minimum temperature required for the fusion of hydrogen is 5 million degrees)

8. When the release of electromagnetic radiant energy (pushing out) reaches a balance with the gravity (pushing in) the star stops contracting and reaches the stable state.  H-R Main Sequence

9. The original mass of the star determines its temperature and the color. (Big – glows blue, medium – glows yellow-orange, small – glows red) Red Giants / Red Super-giants form as H2 fuel is used up and gravity overpowers released energy, center core contracts while outer layer expands (He2 + He2 → C fusion starts in the core) -- outer layers expand and cool (hence it is RED)

10. Hertzsprung-Russell diagram • Each star is represented by a dot. One uses data from lots of stars, so there are lots of dots. The position of each dot on the diagram corresponds to the star's luminosity and its temperature • The vertical position represents the star's luminosity (absolute magnitude). • The horizontal position represents the star's surface temperature (color). http://zebu.uoregon.edu/~soper/Stars/hrdiagram.html

12. Life Cycle of Stars Average to small stars collapse again after C fuel is used up → white dwarf (Earth size) Large stars (at least 7 times our sun) when fusion (of carbon) stops, a central iron core is left, intense gravitational energy causes further collapse, creates heavier elements → explosion causes loss of ½ the stars elements, a supernova is born Supernova fades – neutron star is left (core of pure neutrons), eventually gravity overpowers → black hole is created

14. Constellations – a group of stars that appears to form a pattern in the sky circumpolar constellations – constellations that appear to never set below the horizon: Ursa Major, Ursa Minor, Cephius, Cassiopeia, and Draco

15. Zodiac Constellations Constella-tions that appear along the ecliptic

23. Check this out… • Go and take this quiz: http://aspire.cosmic-ray.org/labs/star_life/starlife_equilibrium.html

25. Good sites • http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html • http://www.astrophysicsspectator.com/topics/stars/FusionHydrogen.html