Fr.: diagonale principale
In the n x n → matrix , the entities a11, a22, ..., ann.
Fr.: lobe principal
The lobe in the reception pattern of a radio telescope that includes the region of the maximum received power. Also called major lobe and main beam.
Fr.: anneau principal
A thin strand of material encircling Jupiter; the main component in → Jupiter's ring system of three parts. The diffuse innermost boundary begins at approximately 123,000 km. The main ring's outer radius is found to be at 128,940 km,
Fr.: séquence principale
An evolutionary stage in the life of a star when it generates its energy by the conversion of hydrogen to helium via → nuclear fusion in its core. Stars spend 90% of their life on the main sequence. On the → Hertzsprung-Russell diagram it appears as a track running from top left (high temperature, high luminosity, high mass) to lower right (low temperature, low luminosity, low mass). See also → zero age main sequence (ZAMS), → terminal age main sequence (TAMS).
sazkard-e reshteh-ye farist
Fr.: ajustement par la séquence principale
The method of determining the distance to a star cluster by overlaying its main sequence on the theoretical zero-age main sequence and noting the difference between the cluster's apparent magnitude and the zero-age main sequence's absolute magnitude.
rahgašt-e rešte-ye farist
Fr.: tournant final de la séquence principale
The point on the → Hertzsprung-Russell diagram of a star cluster at which stars begin to leave the → main sequence and move toward the → red giant branch. The main-sequence turnoff is a measure of age. In general, the older a star cluster, the fainter the main-sequence turnoff. Same as → turnoff point.
Greater in size, extent, or importance.
M.E. majour, from O.Fr., from L. major, irregular comparative of magnus "large, great," cognate with Pers. meh "large, great," as below.
Mehin comparative and superlative of meh "great, large" (Mid.Pers. meh, mas; Av. maz-, masan-, mazant- "great, important," mazan- "greatness, majesty," mazišta- "greatest;" cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- "great") + -in superlative suffix.
Fr.: grand axe
The greatest diameter of an ellipse; it passes through the two foci.
Fr.: fusion majeure
The → merging of two spiral galaxies with roughly equal masses colliding at appropriate angles. The dynamical friction is so efficient that the galaxies merge after only a few perigalactic passages.
Fr.: planète majeure
A name used to describe any planet that is considerably larger and more massive than the Earth, and contains large quantities of hydrogen and helium. Jupiter and Neptune are examples of major planets.
Fr.: prémisse majeur
Fr.: terme majeur
A function, or an element of a set, that dominates others or is greater than all others. In other words, for a function f defined on the interval I, the point M such that for each x on I, f(x)≤ M. See also → minorant.
From Fr. majorant, from majorer "to increase, raise," from L. → major.
Mehân, from mehidan, from meh "great, large," → major.
The greater number, part, or quantity of a whole.
The third largest known → dwarf planet after → Eris and → Pluto. Numbered 136472, and initially called 2005 FYg, it belongs to the → Kuiper belt in the solar system. Discovered in 2005, Makemake is roughly three-quarters of Pluto in size and orbits the Sun in about 310 years.
Named after Makemake "the creator of humanity and god of fertility" in the mythology of the Rapanui, the native people of Easter Island.
durbin-e Maksutof, teleskop-e ~ (#)
Fr.: télescope de Maksutov
A → reflecting telescope incorporating a deeply curved → meniscus, → lens, which corrects the → optical aberrations of the spherical → primary mirror to give high-quality → images over a wide → field of view.
Named for the Russian optical specialist Dmitri Maksutov (1896-1964), who developed the design; → telescope.
Fr.: biais de Malmquist
A selection effect in observational astronomy. If a sample of objects (galaxies, quasars, stars, etc.) is flux-limited, then the observer will see an increase in average luminosity with distance, because the less luminous sources at large distances will not be detected.
Named after the Swedish astronomer Gunnar Malmquist (1893-1982); → bias.
Fr.: correction de Malmquist
A correction introduced into star counts distributed by apparent magnitude.
qânun-e Malus (#)
Fr.: loi de Malus
If the light wave entering an → analyzer is → linearly polarized, the intensity of the wave emerging from the analyzer is I = k I0 cos2φ, where k is the coefficient of transmission of the analyzer, I0 is the intensity of the incident light, and φ is the angle between the planes of → polarization of the incident light and the light emerging from the analyzer.
Named after Etienne Louis Malus (1775-1812), French physicist who also discovered polarization by reflection at a glass surface (1808); → law.
Fr.: méthod de Mamun
A method for deriving the Earth's size based on
measuring a length of meridian between two points corresponding
to the difference between the respective latitudes. The Abbasid caliph
al-Ma'mun (ruling from 813 to 833 A.D.), appointed two teams of surveyors to this
task. They departed from a place in the
desert of Sinjad (nineteen farsangs from Mosul and forty-three from
Samarra), heading north and south, respectively. They proceeded
until they found that the height of the Sun at noon had increased
(or decreased) by one degree compared to that for the starting point.
Knowing the variation of the Sun's → declination
due to its apparent → annual motion, they could relate
the length of the arc of meridian to the difference between the latitudes of
the two places.
They repeated the measurement a second time, and so found that the length of
one degree of latitude is somewhat between 56 and 57 Arabic miles (Biruni, Tahdid).
360 times this number yielded the Earth's circumference, and from it the radius
The seventh Abbasid caliph Abu Ja'far Abdullâh al-Ma'mûn, son of Hârûn al-Rashîd (786-833 A.D.); → method.