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Astronomical system of units

Reference

measured.astronomical

Defines units and constants of use in the field of astronomy, which requires measuring extremely large distances, masses, and periods of time.

The astronomical system of units is a tridimensional system, in that it defines units of length, mass and time. The associated astronomical constants also fix the different frames of reference that are needed to report observations.

Attributes: Units of length

AstronomicalUnit (Unit): A unit representing the average distance between the Earth
    and the Sun; it is now defined precisely as 149,597,870,700 meters

LightYear (Unit): The distance light travels through a vacuum in one `JulianYear`

Spat (Unit): An obsolete unit of astronomical distance equaling 1 trillion meters

Parsec (Unit): A measure of large astronomical distances defined in terms of
    [trigonometry and parallax][1]

    [1]: https://en.wikipedia.org/wiki/Parsec

Siriometer (Unit): An obsolete unit of astronomical distance equaling 1 million AU

Attributes: Units of time

Day (Unit): Uses the same definition of `Day` as the SI system

SiderealDay (Unit): The `Time` it takes the Earth to make one rotation with respect
    to distant stars, approximately 86164.0905 seconds, a few minutes shorter than
    the SI Day.

JulianYear (Unit): defined as 365.25 days of 84,600 SI `Second`

Attributes: Units of mass

SolarMass (Unit): The mass of the Sun

EarthMass (Unit): The mass of the Earth

JupiterMass (Unit): The mass of Jupiter

Attributes: Units for astrophotometry

Jansky (Unit): A unit of spectral flux density

Crab (Unit): A unit for measuring the intensity of astromonical X-ray sources, based
    on the intensity of the Crab Nebula

Attributes: Hubble's Law

H0 (Quantity): Today's estimate of the Hubble Parameter representing the observed
    expansion rate of the universe

HubbleTime (Unit): An approximation of the age of the universe, if the expansion
    rate had been linear

HubbleLength (Unit): The distance at which galaxies are receding from us at the
    speed of light

HubbleVolume (Unit): The sphere within which galaxies are receding from us below
    the speed of light