How far is a light year?

Posted by Admin

Date 27-03-2015 16:03:20

A light-second is the distance light travels in one second, or 7.5 times the distance around Earth’s equator. A light-year is the distance light travels in one year. How far is that? Multiply the number of seconds in one year by the number of kilometers (or miles) that light travels in one second, and there you have it: one light-year. It’s about 9.5 trillion kilometers (5.88 trillion miles).

If we scale the astronomical unit – the Earth-sun distance – at one inch, then the light-year on this scale represents one mile.

The closest star to Earth, other than the sun, is Alpha Centauri at some 4.4 light-years away. Scaling the Earth-sun distance at one inch places this star at 4.4 miles (7 kilometers) distant.

Scaling the astronomical unit at one inch, here are distances to various stars, star clusters and galaxies:

  • Alpha Centauri: 4 miles
  • Sirius: 9 miles
  • Vega: 25 miles
  • Fomalhaut: 25 miles
  • Arcturus: 37 miles
  • Antares: 600 miles
  • Pleiades open star cluster: 440 miles
  • Hercules globular star cluster (M13): 24,000 miles
  • Center of Milky Way galaxy: 27,000 miles
  • Great Andromeda galaxy (M31): 2,300,000 miles
  • Whirlpool galaxy: 37,000,000 miles
  • Sombrero galaxy (M104): 65,000,000 miles

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