2/18/2023 0 Comments Fields of astrometry![]() ![]() Radians are not used in astrometry the basic units are degrees and seconds of arc (denoted”). The physical quantities that are measured by astrometry are angles that are often very small. However, in this article, we shall consider the determination of star positions, the primary goal of space astrometry. As an extension, one ascribes also to astrometry the measurement of apparent dimensions and shapes of celestial bodies. And, because these positions vary with time, the objective is to describe and study these motions that, for stars, provide two essential parameters: the proper motion and the parallax from which the distance is derived. One can define astrometry as the part of astronomy that measures the apparent positions of celestial bodies on the sky. Astrometry is the oldest of all sciences and still is a scientific domain of its own, encompassed by theoretical developments such as stellar dynamics and celestial mechanics now supported by the theory of general relativity. Actually, astronomy has a tradition that goes back to Egyptian, Assyrian, and Greek astronomy. On the other hand, until the second half of the nineteenth century, what is now called astrometric observations were the only astronomical activity that existed. On the one hand, it is essentially an ensemble of techniques that provides some essential data to astronomers and astrophysicists about celestial objects. Astrometry plays a very particular part in the realm of astronomy. ![]()
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