ASTR 103 - Astronomy

Glossary - M

Magellanic Clouds

Pair of irregular galaxies visible to the naked eye in the southern skies. They are our closest optical extragalactic objects.

magnetic field

Region surrounding a magnetized body that acts on electrical particles or currents within its range.

magnetic pole

One of the two diametrically opposite points of a spherical body, or the end points of a bar magnet, where the flux of the magnetic lines of force is maximum.

Magnetosphere

Complete magnetic field that surrounds Earth or any other magnetized planet.

magnifying power

 

magnitude

Brightness of a celestial body based on a logarithmic scale of intensity to which the eye naturally responds.

main sequence

Major distributional segment of the stars running diagonally across the H-R diagram from the upper left to the lower right.

main-sequence fitting

Superposition of the main sequence of a star cluster (plot of apparent magnitude versus color index) over the calibrated main sequence of a star cluster such as the Hyades (plot of absolute magnitude versus color index) to derive the distance modulus of the first cluster and hence its distance.

major axis (of an ellipse)

Longest diameter of an ellipse.

mantle (of a planet)

Intermediate layer between the core of a solid astronomical body and its outer crust.

Mare

Dark marking on the Moon, Mercury, or Mars. (Latin name for sea; plural, maria).

Mass

Amount of matter contained in a body. It is a measure of the inertia possessed by a body when acted on by a force.

mass-luminosity relation

Graph of the absolute magnitudes of the main sequence stars against their masses.

mean solar day

 

mean solar time

 

mechanics

 

megalight year (Mly)

 

mesosphere

Intermediate atmospheric layer above the stratosphere extending approximately between 30 and 100 kilometers above Earth's surface.

Meteor

Luminous trail left behind by the passage of a tiny cosmic particle (meteoroid) through Earth's atmosphere.

Meteorite

Extraterrestrial metallic or stony object that survives flight through Earth's atmosphere and then lands.

Meteoroid

Solid particle or body of small dimensions in extraterrestrial space.

meter (m)

 

meteor shower

Bright streaks appearing to radiate from a common point in the sky; caused by a swarm of meteoroids entering Earth's atmosphere.

micron ( m)

Unit of measure equal to one-millionth of a meter.

Microwave

Radio spectral region in the millimeter to centimeter wavelengths.

microwave radiation (cosmic)

(see also cosmic background radiation).

Milky Way

The name we give to our Galaxy or the band of stars visible in our summer skies.

minor planet

An asteroid. (see also asteroid)

Molecule

Aggregate of two or more atoms of the same or different elements forming a compound.

momentum

A measure of the quantity of motion possessed by a body in a particular frame of reference. Momentum is calculated as the product of a body's mass and its velocity (p = mv).

Monochromatic

Light of a single wavelength or color.

M star

Stars of spectral type M are cool red stars with surface temperatures of less than about 3600 K whose spectra are dominated by molecular bands, especially TiO.

Muon

Elementary charged particle of about 207 electron masses with a half-life of about 1.5-millions of a second. It decays into an electron and a neutrino. Also know as mu-meson.

Mutation

Change in hereditary material. It is produced at random by environmental or other factors.