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Astronomy Contents of the universe. We live in the solar system. Earth orbits the sun every yr in elliptical orbit. Distance Earth to sun 1 AU. Birth of the Solar System Solar system born ~4.5 BYA 2 min. http://www.youtube.com/watch?v=qfdDWdZcpOw. Our Solar System planets/moons/asteriods.
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AstronomyContents of the universe We live in the solar system. Earth orbits the sun every yr in elliptical orbit. Distance Earth to sun 1 AU
Birth of the Solar SystemSolar system born ~4.5 BYA2 min http://www.youtube.com/watch?v=qfdDWdZcpOw
Icy Comets-All orbit the sun -very elliptical orbits
Solar system is part of the milky way galaxy. Orion Arm. The galaxy revolves around black hole. Sun revolution ~ 250 million y.
Galaxies –large aggregates of stars, gas, & dust containing ~ 100 billion (1011) stars ranging in diameter from 1,500 to 300,000 light-years across. Orbit central point. Av distance btw stars 10 ly.
Stars can form stellarclusters w/i galaxies – smaller groups of stars held by gravity. ~ 1000’s of stars.
Constellations – star groups not necessarily near each other.
Galaxies form groups too.Galactic Clusters • Nearest cluster = Virgo cluster
Open Cluster • also galactic cluster- a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. Contain gas and dust
Globular Cluster - older • Generally outside Milky Way in Halo.
Nebulae • Gas clouds – Star nurseries • Formed after Big Bang • from supernova
It’s a long way btw stars.Use Light Years LY The d light travels in 1 yr. • 1 LY = 9.46 x 10 15 m. • 1 AU = 1.5 x 10 11m • 1 pc parsec = 3.09 x 1016 m
Powers of 10 Film 6:30 min http://www.youtube.com/watch?v=tnhken4_-A0
Earth’s Rotation makes stars appear to rotate on fixed sphere.Rotation is around Polaris on 24 h cycle.Sun/planets wander through stellar backdrop.
Stars rotate around Polaris24 hr cycle rise east set westStars appear fixed on sphere relative to each other. http://www.youtube.com/watch?v=JCr_Pz4h2Bw
Know the planets in order, their relative sizes, the asteroids, Kuiper belt. • Clusters, galaxies, nebula
Measuring Stellar Distances • Stellar Parallax few hundred pc • Absolute & Apparent Magnitudes distance • Spectroscopic Parallax • Cepheid variables
Stellar Parallax • Hold up pencil • Blink eyes • Pencil moves against backdrop. • Look at post. • Blink eyes.
Measure Parallax Angle • Angles are very small – measured in arc seconds.
Angular Measurements • expressed in degrees, arc-minutes or arc-seconds. • 360o in circle • 1° = 60 arc minutes. • 1 arcminute = 60 arc sec. • 1 pc= distance where an object has a parallax angle (p) of one arc second.
Stellar Parallaxd = 1/p p = 1/dd (dist) – #parsecs p (parallax angle) – #arc-seconds.
Ex 1: The nearest star to Earth is Alpha Centauri, which is at a distance of 4.37 ly. Calculate the parallax angle that was measured to obtain that distance. • 4.37 LY / 3.26 = 1.34 pc. • p = 1/d 1/1.34 pc • 0.746 arc-sec
Ex 2: A star has a parallax of 0.66 arc sec. A. What is this in parsecs? B. Meters? • d = 1/p • d = 1/ 0.66 = 1.5 pc. • 4.63 x 1016 m.
Why can’t stellar parallax be used to measure very distant stars? • Angle gets too small. Few hundred pc upper limit.
Parallax Method Clip 11 min • https://www.youtube.com/watch?v=XUQAIldqPww