Useful Numbers to Know for Intro Astronomy

The Sky
angular size of a fist at arm's length ≈ 10°
angular size of a finger ≈ 2°
angular size of the Sun ≈ ½°
angular size of the Moon ≈ ½°

Solar  System
Sun to Earth = 1 AU (astronomical unit)
Sun's diameter ≈ 100 x Earth's
Sun's diameter ≈ 1/200 AU
Jupiter's diameter ≈ 10 x Earth's (11 is closer but
          we are using round numbers)
Earth's orbit radius ≈ 100 x Sun's diameter
Moon's diameter ≈ 1/4 Earth's
Moon's distance ≈ 1/400 AU ≈ 30 x Earth's diameter
Solar System diameter (planet orbits) 60 AU

Outside the Solar  System
Nearest star's distance ≈ 4.3 ly (light years) > 270,000 AU
Milky Way galaxy's diameter ≈ 100,000 ly  > billion AU

Matter
size of atoms ≈ 10-10 meters
size of atomic nuclei ≈ 10-15 meters

Light
speed of light,  c = 3 X 108 meters/second
gamma ray wavelength ≈ 1 picometers = 1 X 10-12 meters
microwave wavelengths ≈ 10–20 cm
radio wavelengths = meters to kilometers
approximate limits  of visible wavelengths
blue ≈ 400 nanometers = 4 X 10-7 meters to
red ≈ 700 nanometers = 7 X 10-7 meters