Glosario - M

Magnetosphere is a mostly convex region formed when a plasma, such as the solar wind, interacts with the magnetic field of a body, such as a planet or star.

Magnitude is a numerical scale indicating the brightness of an astronomical object. It is a logarithmic measure where the lower the value, the brighter the object. By convention, a first magnitude star is 100 times as bright as a sixth magnitude star. Magnitude 6 is considered the lower limit of objects that can be seen with the naked eye, although this can vary depending on seeing conditions and eyesight.

Main sequence is a category of stars that form a continuous and distinctive band on plots of stellar temperature versus brightness. These stars are characterized by being in hydrostatic equilibrium and undergoing nuclear fusion of hydrogen-1 in their core region. For example, the Sun is a main sequence star.

Meridian is a line running north-south across the sky and passing through the point directly overhead, known as the zenith.

Messier object is one of a set of 110 'nebulous' objects, of which 103 were catalogued by French comet hunter Charles Messier between 1771 and 1781.

Metallicity is the abundance of elements other than hydrogen and helium. Note that these 'metals' include elements that are not typically considered metallic.

Meteor is the ionization trail produced by a meteoroid as it enters the Earth's atmosphere.

Meteor shower is a series of meteors that seemingly radiate from a point on the night sky. These are produced by debris left over from a larger body, such as a comet, and hence they follow roughly the same orbit. This makes many meteor showers predictable events as they reoccur every year.

Meteoroid is a small rock or boulder that has entered a planetary atmosphere. If it survives to reach the ground, it is then termed a meteorite.

Microvariable is a stellar object such as a variable star that undergoes very small variations in luminosity. Detecting microvariability will typically require sufficient observations to rule out random error as a source.[10]

Minor planet is an object in direct orbit around the Sun that is neither a dominant planet nor originally classified as a comet. A moon is not a minor planet because it is orbiting another body.

Molecular clouds are interstellar clouds where the conditions allow molecules to form, including molecular hydrogen.

Morning width or rise width is the horizontal angular distance between the rise azimuth of a celestial body and the East direction.

Moving group or stellar association is a loose grouping of stars that are traveling together through space. Although the members were formed together in the same molecular cloud, they have since moved too far apart to be gravitationally bound as a cluster.