The 19-inch (482.6 mm) or 23-inch (584.2 mm) dimension refers to the width of the equipment mounting frame in the rack including the frame the width of the equipment that can be mounted inside the rack is less. For example, suppose that a celestial body moved a distance of about 1 arcsec in contrast to other objects in its background, the body then is said to have moved 1 parsec away.Īside from astronomy, there are also other fields where arcsecond is used and one of them is the firearms industry where the accuracy of high-caliber guns is measured in terms of arcseconds and arcminutes. A rack unit, U or RU is a unit of measure that describes the height of equipment designed to mount in a 19-inch rack or a 23-inch rack. To clear things up, arcsec is a measure of an angle, while parsec is a measure of distance. These angles are most of the time so small that they can only be denoted using arcminutes or arcseconds.Īrcsec is also often taken to be related to parsec, another term in astronomy. This unit of measurement is extremely useful in astronomy where the apparent size of a celestial object is usually gauged by means of angular measurements. In the real world, a parsec is a measurement of distance based on apparent stellar motion as observed from Earth. Parsec is a unit of measurement of length.One parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond.A parsec is equivalent to 3.26 light-years. The system used by starship navigators throughout the galaxy to record the location of star systems was based on parsecs, with one unit on the coordinate scale corresponding to 15 parsecs. The term arcsecond is also abbreviated to arcsec, but this term is often confused with the arc secant, which is a trigonometric function that bears the same abbreviation. A parsec was a unit of distance equal to 3.258 light-years.
As an example, 1 arcsecond is written as 1”. (humorous) A unit of measure of 1018 parsecs, or about 3.085. The symbol used to mark an arcsecond is the double quote.
Simply put, it is equal to 1/3600 degrees of an arc.
An arcsecond, also called a second of an arc, is a unit of measurement that amounts to one sixtieth of an arcminute.