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astronomydistances (Distances in space ** )

Astronomy — Distances in space

Distances in Space

  • The distances of the stars are so much greater than any of the distances with which we are familiar that we find great difficulty in comprehending them.
  • The diameter of Earth is about 8,000 miles and that of the Moon about 2,000 miles.  The distance between Earth and the Moon is about 240,000 miles, or 30 Earth diameters.
  • The Sun has a diameter of 865,000 miles and is 93,000,000 miles distant from Earth (1 astronomical unit, or AU).
  • Using the accurate value of 2,160 miles as the Moon’s diameter, we find that the Sun’s diameter is 400 times greater.  Since the Sun’s distance from the Earth is also about 400 time greater than the Moo’s distance, the Sun and the Moon have about the same apparent size of half a degree in the sky.  That is why a total eclipse of the Sun is possible.
  • In AU’s, the distances from the Sun to some of the planets are: 5 for Jupiter, 10 for Saturn, 20 for Uranus, 30 for Neptune, and 40 for Pluto.
  • The nearest star to our solar system (Alpha Centauri) is 272,000 AU’s, or about 25 trillion miles.
  • Distances of stars are commonly expressed in light-years, which is the distance that a photon of light would travel in one year, traveling at the speed of light.  One light year equals 6 trillion miles.  Thus, Alpha Centauri is about 4.3 light years away.  A light year equals 63.310 AU’s.
  • On a scale or map with Earth being just one inch from the Sun, Pluto would be 40 inches away, and the nearest star would be 4.3 miles away.
  • It is convenient to remember that if one inch represents one AU, the 1 mile equals one light year.

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