Astronomy (cont.) Cosmic Measurements Astronomical Unit (AU) - distance from earth to the sun ~150 million kilometers - used to express distances to other planets Light year – distance light travels in one year at 300,000 km/sec - which equals 9.5 x km (If 1 ft. equals 1AU, then 120 miles equals 1 light year)

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!

Properties of Stars Mass & Size → Density - smallest are smaller than Earth - largest are 2000 times bigger than our sun Temperature (color) red → cooler5,000 0 F (3,000 K) blue → hottest 40,000 0 F (30,000 K)

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

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

Life of the Stars: Origin Nebula – huge cloud of gas and dust in space 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 H 2 + H 2 → 2He 2 )  this is electromagnetic radiant energy 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 H 2 + H 2 → 2He 2 )  this is electromagnetic radiant energy

As gravity packs matter more tightly – the protostar’s temperature rises until it reaches a temperature high enough for nuclear fusion to begin 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…. H 2 + H 2 = 2He + electromagnetic radiant energy

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

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 H 2 fuel is used up and gravity overpowers released energy, center core contracts while outer layer expands (He 2 + He 2 → C fusion starts in the core) -- outer layers expand and cool (hence it is RED)

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 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 vertical position represents the star's luminosity (absolute magnitude). The horizontal position represents the star's surface temperature (color). The horizontal position represents the star's surface temperature (color).

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

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

Zodiac Constellations Constella- tions that appear along the ecliptic