StarTalk Sanjay Yengul May 2016 "To know ourselves, we must know the stars."
Twinkle Twinkle How many stars are there? How big are these stars? Picture of night sky What are they made of? Why do they shine? Are they all the same? How are they born how do they die? PHOTO COURTESY NASA The constellation Orion as seen from the space shuttle Endeavour (STS-54)
Astronomical Units 1 AU = distance between earth and the sun 1 Light Year = 63,000 AU = 10 trillion km Speed of light: 300,000 km/s (186,000 miles/s) The Sun is about 8 light minutes away! Our nearest star: Alpha Centauri 4 light years away!
What is a star? A big glowing ball of gas! Contains mainly H and He They have a core that is dense and super hot! Nuclear fusion is the source of their energy! They vary in size, temperature, brightness & color!
How far is that star? For stars < 400 light years away: Parallax or Triangulation For stars farther way: Indirect Method based on brightness measurement
Galaxies A collection of stars Trillions of Galaxies in the Universe Our Galaxy is called the The Milky Way Galaxy It contains billions of stars Age: ~10 billion years, Size: 100,000 light years
Scale of Galaxies
Spectra
Spectral Classes Spectral Class Color Ave.Temp. (K) Familiar Examples O Blue-violet 30,000 Mintaka (delta Orionis) B Blue-white 20,000 Rigel, Spica A White 10,000 Vega, Sirius F Yellow-white 8,000 Canopus, procyon G Yellow 6,000 Sun, Capella K Orange 4,000 Arcturus, Aldebaran M Red-orange 3,000 Antares, Betelgeuse
Star Classification Classes of Stars by Luminosity Class Description Familiar Examples Ia Bright Supergiants Rigel, Betelgeuse Ib Supergiants Polaris (the North star), Antares II Bright Giants Mintaka (delta Orionis) III Giants Arcturus, Capella IV Sub-giants Altair, Achenrar (a Southern Hemisphere star) V Main sequence Sun, Sirius not classified White dwarfs Sirius B, Procyon B PHOTO COURTESY OF NASA The Hertzsprung-Russell Diagram. The Sun, 12 brightest stars of the Northern Hemisphere and white dwarf companion stars to Sirius and Procyon are shown.
Star Classification Classes of Stars by Luminosity Class Description Familiar Examples Ia Bright Supergiants Rigel, Betelgeuse Ib Supergiants Polaris (the North star), Antares II Bright Giants Mintaka (delta Orionis) III Giants Arcturus, Capella IV Sub-giants Altair, Achenrar (a Southern Hemisphere star) V Main sequence Sun, Sirius not classified White dwarfs Sirius B, Procyon B PHOTO COURTESY OF NASA The Hertzsprung-Russell Diagram. The Sun, 12 brightest stars of the Northern Hemisphere and white dwarf companion stars to Sirius and Procyon are shown.
Birth of a star A gravity disturbance causes clumps of gas and dust to collapse inward, heat up In ~ million years a small dense core forms the protostar! When T = 7 million K, fusion starts If the mass is big enough (0.1 solar mass) a new stable star If the mass is not big enough brown dwarf! PHOTO COURTESY OF NASA
Death of a star Stars like the Sun Several billion years later, run out of hydrogen fuel the core contracts under gravity, outer layers expand due to heat Red Giant Burns Helium Planetary Nebula White Dwarf Black Dwarf The Rotten Egg planetary nebula More Massive Stars than the Sun: Burn H, He C Fe Explode into a supernova Neutron Star or a Black Hole Meanwhile the shock from the supernova can initiate star formation in other interstellar clouds Hubble Space Telescope photographs COURTESY OF NASA The rings around Supernova 1987A
Scale of the Universe
References http://stars.astro.illinois.edu/sow/star_intro.html http://stars.astro.illinois.edu/sow/spectra.html http://www.iflscience.com/space/how-big-our-place-universe http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.sht ml Colors and Temperatures: https://docs.kde.org/trunk5/en/kdeedu/kstars/aicolorandtemp.html http://science.howstuffworks.com/star5.htm