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How to Find the Distance of Stars

In a clear night sky, you can see hundreds of celestial objects known as stars that populate our Milky Way galaxy. Because of their vast distance from Earth, scientists measure space objects using light years. A phenomenon we see in our night sky, known as parallax, occurs as the viewer from Earth moves with respect to a moving celestial object. From measuring the right ascension of a star, you can figure out how far away a star is from our planet.

Instructions

- 1
  Locate one star you wish to find the distance of. Using your telescope's measurements, calculate the star's right ascension (RA). The right ascension calculates the position of the west and east horizons measured using hours, minutes and seconds. For the example in this article, use 3.5 RA as the first right ascension measurement.
- 2
  Come back in six months to the exact location of your original right ascension measurement. Calculate the right ascension of the star again. The difference in the two measurements represents the parallax shift of the star as the Earth orbits the sun. For example, if the RA has moved .5 degrees, the RA after five months is four.
- 3
  Subtract the second measurement of the right ascension from the first measurement. Reflect the number in arc-seconds. The arc-second measures the distance the sun rotates around a celestial object, such as the Earth, in one second. The number should be less than one arc-second.
  
  Example: 4 RA - 3.5 RA = .5 arc-seconds
- 4
  Divide one by the arc-seconds to find the reciprocal. This calculation gives the distance of the star measured in parsecs. One parsec is approximately 3.26 light years.
  
  Example: (1) / (.5 arc-seconds) = 2 parsecs
- 5
  Multiple the number in parsecs by 3.26 to find the distance from Earth to the star in light years. A light year is approximately six trillion miles.
  
  Example: 2 parsecs x 3.26 light years= 6.52 light years

Astronomy