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Angular Distance

There are many ways to measure angular distance using your body …

The apparent distance between two celestial objects. It is measured in degrees, arcminutes (an arcminute is a 60th of a degree) and arcseconds (an arcsecond is a 60th of an arcminute). On average, the distance from your thumb tip to the tip of your little finger of your outstretched hand at arms length is 20 degrees. The width of your palm will be about 12 degrees and the width of the tip of your little finger is about 1 degree. The angular diameter of the Moon (and the Sun) is more or less 1/2 degree.

Angular Distance

Angular distance between two astronomical objects

An observer looks at two different objects. The angle between them can be measured e.g. by using a cross staff. This angle is the angular distance of the two objects in the sky. It is expressed in degrees, arcminutes and arcseconds.


The angle measured from the south point of the horizon toward the west to a point at the foot of a star’s vertical circle. When used as an indication of the position of a star on the imaginary celestial sphere it is referred to as Right Ascension.

Celestial Equator

A great circle on the celestial sphere that is midway between the two poles of rotation. It really amounts to the projection of the Earth’s equator onto the sky. It can be thought of as an imaginary ring, 90 degrees from either pole in the sky.

Celestial Latitude

The angle north or south of the ecliptic to an object. Used to help to describe the location of a star on the imaginary celestial sphere.

Celestial Sphere

This does not actually exist. Early humans believed that stars were fixed to a crystal sphere in the sky, at a great distance from Earth. This is because there is no sense of distance in the night sky and the stars always seemed to be fixed in position relative to each other. The idea is a handy one when dealing with positioning and angles between objects in the sky. See also celestial latitude, longitude, azimuth.

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