megajanskys

Megajansky (MJy) is a unit of spectral flux density used in radio, infrared, and submillimeter astronomy. It equals one million janskys (1 MJy = 10^6 Jy). Since 1 Jy is 10^-26 W m^-2 Hz^-1, 1 MJy corresponds to 10^-20 W m^-2 Hz^-1.

Because many astronomical sources are relatively bright at radio and submillimeter wavelengths, MJy is convenient for expressing total flux densities of extended sources or high-brightness regions. In map-based work, the related unit megajansky per steradian (MJy sr^-1) or megajansky per beam is often used to express surface brightness.

The Jansky is a non-SI unit that remains widely used in astronomy. The mega- prefix simply scales the unit by a factor of one million, so values in MJy can be converted to Jy by multiplying by 10^6, and to SI units by multiplying by 10^-26.

Example: a source with a flux density of 25 MJy has 25 million Jy, which is 2.5×10^7 Jy, corresponding to 2.5×10^-19 W m^-2 Hz^-1 in SI units.

Origin and usage: The unit Jansky is named after Karl Jansky, a pioneer of radio astronomy. Megajansky inherits the same naming convention, with the prefix indicating a multiplier of one million for practical expression of bright astronomical flux densities. Related concepts include flux density, surface brightness, and the use of MJy in astronomical maps.