Astronomical system of units

Astronomical units are used to meet the specific needs of astronomy accessible ( the term is not to be confused with the Astronomical Unit, which is one of these units). Incorporated are also some typical astronomical systems of measurement and their characteristics.

Introduction

Compared to the familiar to us ( terrestrial ) units, the magnitudes in astronomy are often literally " astronomical ," and the human notion threatens to fail: So, the distance from our Sun to the nearest star ( Proxima Centauri ) about 40 trillion kilometers; our sun weighs approximately 1.9891 · 1030 kg. One can compare these values ​​while with others, but it threatens every sense of the magnitude of being lost.

Therefore, one often used in astronomy relationships with familiar sizes to get an easier comparison.

  • For distances above the light-year is often used ( the distance that light travels in a year), a fact that laymen often irritated because the term " year " indicates a period of time.
  • The mass of stars, planets and other astronomical objects is often given in multiples of the mass of other objects, for example, in units of the sun or the earth's mass.
  • The specification of an angle in rotationally bound coordinate systems in the time dimension, that respond to the intuitive approach to the rotation period, such as the Earth Day, so 24 hours instead of 360 degrees, for example = 1h 23m 45s sidereal time.

Masses

The following astronomical units also not part of the International System of Units. In astronomy, they are largely inevitable and will therefore also be used. The light-year is not used by astronomers in specialist use in the rule.

Time

After an astronomical convention Priority

  • Times in the form of 1h 23m 45s, modern and 01:23:45,
  • But durations in the form of 1 h 23 m 45 s at.

The time is specified with ' and' is not usual to avoid confusion with angular minutes and seconds of arc.

Performance

There is also the convention to illustrate certain benefits in that one compares, for example, with the radiant power of the sun, an entire galaxy or equal to the entire universe.

Brightness

The apparent brightness ( magnitude or magnitudo m) is defined generally

With I1, 2 radiation intensity (energy per time and area in Js -1m -2 = Wm -2). This is a pure measure of comparison, so you need a Maßnormal:

Amateur Solar mass Earth mass Astronomical symbols Convention (norm) Solar constant Full moon International Astronomical Union Jet Propulsion Laboratory
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