## How do you calculate the azimuth and altitude of an object? (Intermediate)

I just wanted to know how to calculate the azimuth and the altitude of an object - an example would be really helpful.

The altitude of an object is its angular distance from the horizon, and the azimuth is generally defined as its angular distance from due north, measured eastward. To calculate the approximate altitude and azimuth for an object, then, you need to estimate those angular distances. A simple way to do this is to remember that the full Moon is approximately half a degree in size as seen from the Earth; alternately, the angular size of your thumb when you hand is stretched out and your are giving a "thumbs up" is also about half a degree. So, you can estimate the number of "thumbs" between the horizon and the object and due south and the object to get a rough estimate of its altitude and azimuth.

Keep in mind that since altitude and azimuth are measured relative to your position on the Earth, they will change both with location and with time of night. So, an object at an altitude of 30 degrees at midnight will not have an altitude of 30 degrees at 3am (unless you are at the North or South pole), nor will it have the same altitude at another location on the Earth.

#### Kristine Spekkens

Kristine studies the dynamics of galaxies and what they can teach us about dark matter in the universe. She got her Ph.D from Cornell in August 2005, was a Jansky post-doctoral fellow at Rutgers University from 2005-2008, and is now a faculty member at the Royal Military College of Canada and at Queen's University.

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