| Mab |
A moon of Uranus was discovered by Mark R. Showalter and Jack J. Lissauer using the Hubble Space Telescope on August 25, 2003. Mab is also designated as "Uranus XXVI" and "S/2003 U1". Queen Mab, a fairy queen from English folklore who is mentioned in William Shakespeare's play Romeo and Juliet. |
| Magnitude |
A measure of the apparent brightness of a celestial object. |
| Maine Rule |
The rule for calculating a Blue Moon as the third Full Moon in a season with four Full Moons. It is named the "Maine Rule" from The Maine Farmers' Almanac. Seasons however are based on the circular orbit of a fictitious mean Earth defined from the Ecclesiastical Vernal Equinox (March 21) inferring Summer Solstice as June 22, Autumnal Equinox as September 23 and Winter Solstice as December 22 (Yule). |
| Maksutov-Cassegrain |
A catadioptric telescope design characterized by a thick deeply curved Corrector Plate and usually an f/15 focal ratio. |
| Margaret |
A moon of Uranus was discovered by Matthew Holman on August 13, 2001. Margaret is also designated as "Uranus XXIII" and "S/2003 U3". Margaret is the servant of Hero in William Shakespeare's play Much Ado About Nothing. |
| Mars |
Mars is the fourth planet from the Sun. Mars' diameter is 6,790 km and takes 687 days to orbit the Sun. Mars is named after the Roman god of war. In Eastern Asian cultures Mars is also known as the 'Fire Star.' |
| Martian |
Having to do with the planet Mars. |
| Mass |
The total amount of material in an object. |
| Measuring Engine |
A machine used to measure the position and brightness of objects on photographic plates. |
| Megaclite |
A moon of Jupiter was discovered by Scott Sheppard and team in 2000. Megaclite is also designated as "Jupiter XIX" and "S/2000 J8". |
| Mensa |
The constellation "The Table Mountain" |
| Mercurian |
Having to do with the planet Mercury. |
| Mercury |
Mercury is the closest planet to the Sun. Mercury's diameter is 4880 km and takes 88 days to orbit the Sun. Mercury is named after the Roman messenger god. In Eastern Asian cultures Mercury is also known as the 'Water Star.' |
| Meridian |
A reference line in the sky that goes from one celestial pole to the other and passes through the zenith, dividing the eastern and western halves of the sky. |
| Messier Object |
A non-stellar celestial object listed in the Messier Catalog. |
| Meteor |
A fragment of material from space which falls into Earth's atmosphere and vaporizes. |
| Methone |
A moon of Saturn was discovered by the Sebastien Charnoz on June 1, 2004. Methone also is designated as "Saturn XXXII" and "S/2004 S1". In Greek mythology, Methone was one of seven (beautiful) daughters of the giant Alkyoneus. |
| Metis |
A innermost moon of Jupiter was discovered by Steven Synnott in March 4, 1979. Metis is also designated as "Jupiter XVI" and "S/1979 J3". In Greek mythology, Metis was the first wife of zeus and the mother of Athena. |
| Microphotometer |
A machine used to measure the brightness of an object or a spectral line on a photographic plate. |
| Microscopium |
The constellation "The Microscope" |
| Milk Moon |
The name of the Full Moon usually in May. Specifically the second Full Moon after Ecclesiastical Vernal Equinox (March 21). Sometimes called the "Flower Moon" or "Corn Planting Moon." |
| Milky Way Galaxy |
The galaxy in which our solar system resides. |
| Mimas |
A moon of Saturn was discovered by William Herschel in 1789. Mimas also is designated as "Saturn I". In Greek mythology, Mimas was a giant slain by Heracules. |
| Miranda |
A moon of Uranus was discovered by Gerard P. Kuiper on February 16, 1948. Miranda is also designated as "Uranus V". Miranda is Prospero's daughter in William Shakespeare's play The Tempest. |
| Mirror Coatings |
Dielectric or aluminum coatings deposited on first-surface mirrors to greatly enhance reflectivity. |
| Mirror Lock |
A feature in some catadioptric optical systems hat allows the focusing mirror to be loced into positions so that a "zero image shift" focuser can be used, usually for astro-imaging. |
| Mneme |
A moon of Jupiter was discovered by Scott S. Sheppard and team in 2003. Mneme is also designated as "Jupiter XL" and "S/2003 J21". In Greek mythology, Mneme was one of the three original Muses. |
| Monoceros |
The constellation "The Unicorn" |
| Moon After Yule |
The name of the Full Moon usually in January. Specifically the first Full Moon after Yule (December 22 by "The Maine Rule"). Sometimes known as the "Wolf Moon" or "Old Moon." |
| Moon Before Yule |
The name of the Full Moon usually in December Specifically the first Full Moon before Yule (December 22 by "The Maine Rule"). Sometimes called the "Cold Moon" of the "Long Night Moon." |
| Morning Star |
Either Mercury or Venus, whichever is most prominent, when it appears in the morning sky before sunrise. |
| Mount |
The mechanical portion of a telescope system which connect the telescope tube to a tripod or pier. There are two kinds of mounts: an Altazmuth mount whose motion is oriented left-right/up-down and an Equatorial mount which is angle at the latitude and whose motion is oriented around the motion of the celestial sphere. |
| Mundilfari |
A moon of Saturn was discovered by Brett Gladman in 2000. Mundilfari also is designated as "Saturn XXV" and "S/2000 S9". In Norse mythology, Mundilfari was a giant and the father of the god Sol. |
| Musca |
The constellation "The Fly" |
