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HD 141569 is an isolated [5] Herbig Ae/Be star [6] of spectral class A2Ve [7] approximately 364 light-years away in the constellation of Libra. The primary star has two red dwarf companions (orbiting each other) at about nine arcseconds. In 1999, a protoplanetary disk was discovered around the star.
Stellar parallax measures are given in the tiny units of arcseconds, or even in thousandths of arcseconds (milliarcseconds). The distance unit parsec is defined as the length of the leg of a right triangle adjacent to the angle of one arcsecond at one vertex, where the other leg is 1 AU long.
The amount of shift is quite small, even for the nearest stars, measuring 1 arcsecond for an object at 1 parsec's distance (3.26 light-years), and thereafter decreasing in angular amount as the distance increases. Astronomers usually express distances in units of parsecs (parallax arcseconds); light-years are used in popular media.
A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (not to scale). The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).
This number is likely much higher, due to the sheer number of stars needed to be surveyed; a star approaching the Solar System 10 million years ago, moving at a typical Sun-relative 20–200 kilometers per second, would be 600–6,000 light-years from the Sun at present day, with millions of stars closer to the Sun.
This is an accepted version of this page This is the latest accepted revision, reviewed on 1 February 2025. General-purpose programming language "C programming language" redirects here. For the book, see The C Programming Language. Not to be confused with C++ or C#. C Logotype used on the cover of the first edition of The C Programming Language Paradigm Multi-paradigm: imperative (procedural ...
A contemporary German popular astronomical book also noticed that light-year is an odd name. [25] In 1868 an English journal labelled the light-year as a unit used by the Germans. [26] Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations. [27]
Epsilon Eridani has a high proper motion, moving −0.976 arcseconds per year in right ascension (the celestial equivalent of longitude) and 0.018 arcseconds per year in declination (celestial latitude), for a combined total of 0.962 arcseconds per year. [1] [note 5] The star has a radial velocity of +15.5 km/s (35,000 mph) (away from the Sun ...