Astronomical units of length
- Astronomical units of length
Astronomers use a number of different length units for different objects. The length unit used is typically determined by two criteria:
#the unit should create manageable numbers
#the unit should be easily derivable from observation
The distances are closely related to the cosmic distance ladder.
Units used for various astronomical distances
The distances to distant galaxies are typically not quoted in distance units at all, but rather in terms of redshift. The reasons for this are that converting redshift to distance requires knowledge of the Hubble constant which was not accurately measured until the early 21st century, and that at cosmological distances, the curvature of space-time allows one to come up with multiple definitions for distance. For example, the distance as defined by the amount of time it takes for a light beam to travel to you is different from the distance as defined by the apparent size of an object.
Wikimedia Foundation.
2010.
Look at other dictionaries:
Astronomical unit — This article is about unit of length. For the full system of units, see Astronomical system of units. 1 astronomical unit = SI units 149.60×10^6 km 149.60×10^9 m Astronomical units 4.8481 … Wikipedia
Length — is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end. This may be distinguished from height, which is vertical extent, and width or breadth, which are the… … Wikipedia
astronomical unit — Astron. a unit of length, equal to the mean distance of the earth from the sun: approximately 93 million miles (150 million km). Abbr.: AU [1900 05] * * * ▪ unit of measurement Comparative data for the Sun, planets, and other solar system… … Universalium
astronomical unit — (ua or au or AU) a unit of distance used by astronomers to measure distances in the Solar System. One astronomical unit equals the average distance from the center of the Earth to the center of the Sun (mathematically, it is the length of the… … Dictionary of units of measurement
Units of measurement — Weights and measures redirects here. For other uses, see Weights and measures (disambiguation). The former Weights and Measures office in Seven Sisters, London A unit of measurement is a definite magnitude of a physical quantity, defined and… … Wikipedia
Units of Measurement — Do you know the story of the facetious unit of beauty called the millihelen ? Since it is that the astonishingly beautiful Helen of Troy had a face that launched a thousand ships , a millihelen is a unit of beauty equal to the ability to launch… … Phrontistery dictionary
Conversion of units — is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors. Contents 1 Techniques 1.1 Process 1.2 Multiplication factors … Wikipedia
List of unusual units of measurement — For units of measure primarily used in countries where English is not the main language, see the article specific to that country, a list of which can be found in the systems of measurement article. An unusual unit of measurement is a unit of… … Wikipedia
International System of Units — SI redirects here. For other uses, see Si (disambiguation). Cover of brochure The International System of Units The International System of Units[1] (abbreviated SI from French: Système international d unités[2]) is the modern … Wikipedia
Centimetre–gram–second system of units — CGS redirects here. For other uses, see CGS (disambiguation). The centimetre–gram–second system (abbreviated CGS or cgs) is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit… … Wikipedia
