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°

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
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

Nearest star's distance ≈ 4.3 ly
(light years) > 270,000 AU

Milky Way galaxy's diameter ≈ 100,000 ly > billion 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

size of atomic nuclei ≈ 10

Light

speed of light, c = 3 X
10^{8} 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

gamma ray wavelength ≈ 1 picometers = 1 X 10

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

red ≈ 700 nanometers = 7 X 10