Usual measurement units in astronomy

For distances within our solar system, or other solar systems, the common unit is the Astronomical Unit (A.U.) 1 A.U. = the average distance between the Earth and the Sun
For most everything else, stars,galaxies,etc..., the distance unit is the parsec (pc). This is a convenient unit when measuring distances to stars by triangulation (what astronomers call parallax).
1 pc = 3.26 light years = about the distance to the nearest star
1 pc = 60 x 60 x 180/pi A.U. = 206265 A.U. ( by definition).
for distances within our galaxy or other galaxies it is kiloparsecs (kpc):
1 kpc = 1,000 pc
for distances between galaxies, and cosmology it is Megaparsecs (Mpc):
1 Mpc = 1,000,000 pc
The convenient astronomical mass unit is the mass of the Sun. One Solar mass is 2x10exp30kg
It is also convenient to mesure the luminosities of celestial objects in terms of the bolometric luminosity of the Sun ( 3.90x10exp26W).
The flux density is the energy incident per second per unit area pr unit frequency band at the Earth. The S.I.units of flux density are watts per square meter per hertz. The typical flux densities of the astronomical objects are wery small and so the radioastronomers introduced the unit 10exp(-26)W/squar meter xHz witch is known as 1Jansky (1 Jy)
In optical astronomy the traditional systems of optical magnitudes is still commonly used:
m=constant-2.5 log S were S is the flux density of the object. The magnitude system is normalized so that a standard star, chosen to be Vega in the constellation of Lyra has zero magnitude.