What is Astrometry

Quite simply, astrometry is a field within astronomy that deals with the positions and movements of celestial bodies.  Emphasis is placed on accurately determining the movement of stars and other objects.  Astrometry uses this information to provide information about how the bodies in our solar system and galaxy move.

Astrometry has been pursued since ancient times, when people like Hipparchus used star catalogues to track the movements of celestial bodies.  Ptolemy used a catalogue that ended up having 850 stars in it for reference.  Since then, astrometry has grown to become just one field of astronomy as our knowledge of the universe has increased.

Astrometry today is concerned with measuring the distances between stars using triangulation.  In this process, angles between two celestial bodies are measured as precisely as possible using a telescope.  Astronomers will use reference stars and charts to find the angle that a new star is in relation to several known ones.  Then, they are able to find an approximate position of the new object.

Careful steps are taken in the process of measuring the stars in order to ensure accuracy.  One source of error that astronomers have to watch out for is the turbulence in the Earth’s atmosphere, which can bend the light coming into the telescope from the stars.  Error can also come from the instrument itself, if it is not properly calibrated and maintained for the job.  It is important to have an accurate of a measurement as possible, because the stars are constantly moving even as our Earth is.

Astrometry uses a celestial coordinate system to track objects in the night sky.  This system, called the equatorial system, has the Earth’s equator as a plane projected into the sky.  Right Ascension (RA) is the angle in the plane from 0 to 24 hours around the Earth, and Declination is the angle orthogonal to RA, from -90 degrees at the celestial south pole to 90 degrees to the celestial north pole.

Astrometry is useful in many fields of astronomy and physics, as it is very important in understanding the nature of the stars and galaxies around us.  For instance, it has been used to more accurately determine the Earth’s rotation, as well as do dynamic studies on the motion of the Milky Way galaxy.  From proving Einstein’s theory of relativity to celestial mechanics and cosmology, astrometry has very important applications in astrophysics and the study of the universe.