astronomical unit

(noun)

The mean distance from the Earth to the Sun (the semi-major axis of Earth's orbit), approximately 149,600,000 kilometres (symbol AU), used to measure distances in the solar system.

Related Terms

Examples of astronomical unit in the following topics:

  • Length

    • In most systems of measurement, the unit of length is a fundamental unit, from which other units are defined.
    • There are several units that are used to measure length.
    • The centimeter and the kilometer, derived from the meter, are also commonly used units.
    • In U.S. customary units, English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile.
    • Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec.

  • Spectra

    • and $F_\nu$ is called the specific flux.The use of $F_\nu$ is so common that astronomers have a special unit to measure $F_\nu$
    • This unit is most commonly used in the radio and infrared, and sometimes in the x-rays.A common combination that people use is
    • This is really handy since astronomers like to use log-log plots.

  • Kepler's Third Law

  • Celsius Scale

    • Celsius, or centigrade, is a scale and unit of measurement for temperature.
    • It is one of the most commonly used temperature units.
    • The unit of measurement is the degree Celsius (°C).
    • It is one of the most commonly used temperature units in the world.
    • The unit system is named after the Swedish astronomer Anders Celsius (1701-1744), who developed a similar temperature scale .

  • An Astronomical Aside: Magnitudes

    • Astronomers typically speak about the flux of an object in terms of magnitudes.
    • where $f_\nu$ is the flux in c.g.s.units.

  • Prefixes and Other Systems of Units

    • SI prefixes precede a basic unit of measure to indicate a multiple or fraction of the unit.
    • A metric prefix, or SI prefix, is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit.
    • Some units that are widely used are not a part of the International System of Units and are considered Non-SI Units.
    • These units, though not officially part of SI Units, are generally accepted for use in conjunction with SI units.
    • Apply prefixes to units and distinguish between SI and customary units

  • Converting Units

    • It is often necessary to convert from one type of unit to another.
    • Conversion of units is the conversion of different units of measurement for the same quantity, typically using conversion factors.
    • In this case, you will need to convert units of feet to miles.
    • This method cannot be used between units that have a displacement, or difference factor.
    • Physically crossing out units that cancel out helps visualize the "leftover" unit(s).

  • Matter and Antimatter

    • Antimatter galaxies, if they exist, are expected to have the same chemistry and absorption and emission spectra as normal-matter galaxies, and their astronomical objects would be observationally identical, making them difficult to distinguish from normal-matter galaxies.

  • Infrared Waves

    • Many astronomical objects emit detectable amounts of IR radiation at non-thermal wavelengths.
    • Observations of astronomical UV sources must be done from space.

  • Gamma Rays

    • Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced.
    • A large fraction of such astronomical gamma rays are screened by Earth's atmosphere and must be detected by spacecraft.