1. UpdatedCreated by C. Ippolito March 2009 Stars and their Characteristics Early Observations Distances to Stars Mass, Size, Temperature Life Cycles of Stars

2. UpdatedCreated by C. Ippolito March 2009 Early Observations Constellations –groups of stars visualized as “entities” Big Dipper –best known asterism –part of Ursa Major Little Dipper –contains polaris (North Star) –part of Ursa minor

3. UpdatedCreated by C. Ippolito March 2009 Apparent Magnitude measures how bright a star appears to an observer on Earth –First Magnitude (Alpha) brightest –Sixth Magnitude faintest –can’t be seen by unaided eye

4. UpdatedCreated by C. Ippolito March 2009 Distances to Stars Sun –150 million km = 1 astronomical unit (AU) Proxima Centauri –400 trillion km = 260,000 AU Light year –distance light travels in 1 year 300,000 km/s = 9.5 trillion km/year Proxima Centauri –4.2 light years away Parallax –change of object’s direction based on observers position parsec (1 parsec = 3.258 light years = 3.086 x 10 13 km

5. UpdatedCreated by C. Ippolito March 2009 Mass, Size, Temperature, Color Mass –measured in solar masses (# x sun mass) Color –related to temperature bluish white (He) –9,500 °C and above white (He) –7,000 °C to 9,500 °C yellow white (H) –6,000 °C to 7,000 °C yellow (H) 5,200 °C to 6,000 °C yellow/orange (H) – 3,900 °C to 5,200 °C red (titanium oxide) – below 3,900 °C

6. UpdatedCreated by C. Ippolito March 2009 Life Cycle of Stars Hertzsprug-Russell Diagram –plots the luminosity vs. surface temperature –“stages” of life Main Sequence Stars –90% of stars –high luminosity/surface temp to low luminosity/surface temp Supergiants –100x sun (Betelguese) Giant Stars –10x sun (Polaris, Acturus) White Dwarfs –end of life cycle –former red giants w/o atmosphere

7. UpdatedCreated by C. Ippolito March 2009 Birth of a Star nebula –99% hydrogen 1% fine dust (.0001 cm) protostar –gravity compresses particles main sequence –longest stage –H fusion to He red giant or red super giant –H gone, core contracts –shell expands planetary nebula or supernova –absorb halo of gases or iron core absorbs energy and explodes white dwarf or black hole or neutron (pulsar) star