How to Calculate Azimuth

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Have you ever gazed into the night sky and wondered how to describe the locations of the objects you see? Astronomers use azimuth and altitude to do this. Azimuth is the direction of an object in the sky, measured in degrees, while altitude is the height of an object above the horizon. Because of the Earth’s rotation, the azimuth and altitude both change over time as the stars appear to move across the night sky. Satellite dishes also use azimuth and altitude for pointing at the appropriate broadcasting satellites in the sky.

TL;DR (Too Long; Didn't Read)

The azimuth of an object is its direction in the sky, measured in degrees. Azimuth corresponds to the cardinal directions on land: north at 360 degrees, east at 90 degrees, south at 180 degrees and west at 270 degrees. Using a compass and the North Star, you can calculate the azimuth for any object in the sky.

  1. Use a compass to find north

  2. Use the compass to determine north. This gives you your "0" degree point for azimuth.

  3. Point the compass in the direction of the object

  4. Turn the compass to point in the direction with the azimuth you want to measure. The degree reading on the compass is your object’s azimuth.

  5. Locate the North Star, Polaris

  6. After dark, locate the North Star called Polaris to calculate azimuth. The North Star is almost exactly due north, giving the star an azimuth of "0" degrees.

  7. Find the distance between the North Star and the object

  8. Measure the distance, in degrees, between the North Star and your object. If the object is in the east, the distance to the east will equal your object’s azimuth. For example, a star located 45 degrees east of due north has an azimuth of 45 degrees.

  9. Calculate azimuths

  10. For an object west of the North Star, the azimuth is 360 degrees minus the distance measured. Use the following formula to calculate azimuths to the west: Z = 360 - d, where "Z" is the azimuth you want to find, and "d" is the distance (in degrees) from due north. For example, if you measure a star to be 70 degrees from due north, its azimuth is 290 degrees or

    Z = 360 - 70 = 290.

    Tips

    • You can use your fist, held at arm’s length with the back of your hand facing you, to estimate the azimuth of an object. Although fists vary in size, your fist is approximately equal to 10 degrees.

    Warnings

    • Do not use a compass close to metal buildings as these can affect the compass readings.

References

About the Author

Laurel Brown has several years experience as an educator and a writer. She won the 2008 Reingold Prize for writing in the history of science. Brown has a Ph.D. and Master of Arts in the history of science and Middle Eastern studies from Columbia University, as well as a Bachelor of Arts in astrophysics from Colgate University.

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