Back to Astro 103 main page
### MATERIAL FROM CLASS 11: Monday October 16

Lengths:

1AU = 1.5 x 10^{8}km or 1.5 x 10^{11}km

1 km (kilometer) = 1000 meters = 5/8 mile

1 meter = 1000mm (millimeters), so 1mm = 10^{-3}meters

1 meter = 10^{6}microns, so 1mm = 10^{-6}meters

1 meter = 10^{9}nm (nanometers), so 1nm = 10^{-9}meters

Apparent brightness f
= luminosity L/(4 &pi d^{2})

L is in watts, so f is in W/square meter when distance d is in meters.

The Sun is BIG: its radius is almost twice as large as the Moon's orbit around
the Earth: