How to Calculate the Angular Distance Between Places

If you have ever wondered how far apart two stars really are, you certainly aren’t the first such person in history. Until recently, actually measuring the distance between stars was impossible, so early astronomers employed tricks. Angular distance is once such trick, where you report not the actual distance, but the apparent distance between two points. Although this method is most often used to measure astronomical objects from Earth, it could be used for any two places, whether on Earth or in the sky, that can be seen from the physical position of an observer.

Instructions

    • 1

      Stand in a position where both stars or places can be seen. Imagine you are standing at a point of a triangle where two sides of that triangle extend out, one to each star. Therefore, the angle describing the point where you stand is the angular distance.

    • 2

      Measure the angular distance. Astronomy students may have access to an Astronomer's Crossbow, as shown by Robert Knop at Vanderbilt University, to make measurements. If this is the case, then a distance of 1 inch on the crossbow represents 2 degrees angular distance. If you don't have a crossbow, you can use the fist-finger rule for determining distances. Extend your arm out its full length toward the area between the objects to be measured. Use the tip of your pinkie, your middle three fingers, or the width of your fist to determine the distance between the two objects: 1, 4 and 10 degrees respectively. If you extend your fingers out as far as you can, the distance between the outside of your pinkie to the outside of your thumb is 18 degrees.

    • 3

      Record measurements along with date and your location. If measurements were made with an Astronomer's Crossbow, record both the measurements in inches and then convert to degrees, assuming that 1 inch is equal to 2 degrees.

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