Massive Compact Halo Objects. Low-luminosity objects such as planets and brown dwarfs which contribute to the mass of the galactic halo.
Magellanic clouds
Small, irregular galaxies that are companions to the Milky Way. Visible in the southern sky.
magnitude scale
The astronomical brightness scale. The larger the number, the fainter the star.
main sequence
The region of the H-R diagram running from upper left to lower right, which includes roughly 90 percent of all stars.
mass-luminosity relation
The more massive a star is, the more luminous it is.
megaparsec (Mpc)
A unit of distance equal to one million parsec.
Milky Way Galaxy
The spiral galaxy containing our sun. Visible on the northern hemisphere in summer in the night sky as the Milky Way, a faint band stretching over the sky.
minute of arc (arcminute)
Measure of angle. A full circle equals 360 degree. 1 degree equals 60 arcminutes.
1 arcminute equals 60 arcseconds.
model
A tentative description of a phenomenon for use as an aid to undestanding.