astrotalk2006 barycenter moon（astrotalk2006重心的月亮）.pdfVIP

Barycenter of Solar System Earth-Moon barycenter? Moon orbits … what? Dr. Scott Schneider Dr. Scott Schneider Friday Feb 24th, 2006 Sponsored by the Society of Physics Students (SPS) Webpage : /s_schneider/astro/astroweek_2006.shtml Brought to you by … • The Letter Q (as in Quisp) • The number 3.1415 • Code Red! • Diet Coke (after the sugar shakes set in) • …. Britney Spears? Who orbits what? • Planets in the solar system orbit the Sun? • Actually they orbit the “center of mass” – Called the “barycenter” of the solar system • Barycenter has “smooth” path through galaxy (but Sun/planets “wiggle”) – Earth/Moon system also has a barycenter How do you calculate the barycenter? • Start with – how to you find the positions of the planets • Fancy dancy powerful computers can calculate the positions based on Newton’s law of Gravity (and Einstein (JPL) • Those “time series” (way too large to be ‘emailed’) can be analyzed (VSOP theory) • Fourier series approximation (based on time) – Now you just need to know the coefficients – Can then reconstruct the position information To find the planet locations … • Pick a planet .. (poor Pluto too tough, but too far away) • Pick a date … • Pick a coordinate system … – Heliocentric = measured from the Sun (center) • Earth-Sun plane – “point of Aries” (Earth-Sun: Spring) – Geocentric = measured from Earth (center) • Get back either X, Y, Z … – Measured in Astronomical Units (AU) (Earth-Sun distance) • or l (longitude), b (latitude), r (radial distance) “Just” some sums … (many!) • For each of the coordinates (x, y, z or l, b, r) – have up to 5 coefficients for a “time polynomial” • Coeffici