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Angular measurements in the sky

Most of the objects, which are investigated in astronomy, not subject to direct observation, therefore, all information about them can be obtained only on the basis of a comprehensive study, light coming from them (or other radiation). About, as light is analyzed qualitatively and quantitatively, we will learn more. While it is important for us, what in the direction of the light beam, coming from a celestial body (lights), you can set its position in the sky. This is done by angular measurements.

So, the angle between the telescope, aimed at a celestial body, and the plane of the horizon is called its altitude above the horizon. The angle between the directions of two stars determines the angular distance between them. Of course, the angular distance between celestial bodies only describes their relative positioning in the sky. If, for example, two stars are from each other at a small angular distance and seem to be located near, it does not mean, they are really close to each other. One of them may be many times farther from the Earth, than the other. Photographing the sky and measuring the photo distance between the stars, astronomers are star atlases and maps, the schema, and lists the exact coordinates of stars.

Angular measurements on the sky are produced not only in a variety of astronomical observations, but is widely used since ancient times, in navigation to navigate by the sun and the stars. Currently, the sun and the stars are orientation of satellites and spacecraft.

Angular measurements are also needed to determine the size of celestial bodies. It is easy to understand, what are the visible dimensions of the luminaries depend on distance. For example, the angular diameter of the Sun, t. e. the angle between the directions at diametrically opposite points of the solar disk, 0.5°. The moon is approximately 400 times less than the Sun, but at the same time closer to the Ground; therefore it has the same angular diameter during solar eclipses can completely cover us from the Sun. The stars so distant from us, in the most powerful telescopes are visible in the form of points, although it is known, many of them are much more Sun.

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