Astron

In astronomy and celestial navigation , an ephemeris (plural: ephemerides ; from Latin ephemeris, "diary", from Greek : ἐφημερίς , ephēmeris , "diary, journal") [1] [2] [3] [4] gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times. Historically, positions were given as printed tables of values , given at regular intervals of date and time. Modern ephemerides are often computed electronically from mathematical models of the motion of astronomical objects and the Earth. Even though the calculation of these tables was one of the first applications of mechanical computers , printed ephemerides are still produced, as they are useful when computational devices are not available. The astronomical position calculated from an ephemeris is given in the spherical polar coordinate system of right ascension and declination . Some of the astronomical phenomena of interest to astronomer...

A parsec (symbol: pc ) is a unit of length used to measure large distances to objects outside our Solar System . One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond . [1] A parsec is equal to about 3.26 light-years (31  trillion kilometres or 19 trillion miles ) in length. The nearest star, Proxima Centauri , is about 1.3 parsecs (4.25 light-years) from the Sun. [2] Most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun. https://en.wikipedia.org/wiki/Parsec