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Astro*Dictionary by Michael Erlewine

 

 

 

 

21 articles for "Mean"

Mean Anomaly [Astro*Index]

The true anomaly is a body's angular distance from its perihelion to a point in its orbit. For computational convenience, astronomers use a mean planet, which coincides with the body at perihelion and aphelion, but moves with a uniform angular velocity equal to the mean angular velocity of the true planet. The mean anomaly is the anomaly of this ficticious body.

See also:
♦ Kepler Laws ♦ True Anomaly ♦ Perihelion ♦ Aphelion ♦ Angular Velocity
Mean Anomaly [Munkasey M.]

The Anomaly determined from using the Mean Sun.

See also:
♦ Kepler Laws ♦ True Anomaly ♦ Perihelion ♦ Aphelion ♦ Angular Velocity
Mean Daily Motion [Astro*Index]

The mean angular motion of a body in one ephemeris day.

G e o c e n t r i c a l l y :
Moon13°11'
Mercury23'
Venus12'
sun59'
Mars31'
Jupiter5'
Saturn2'
Uranus42"
Neptune24"
Pluto15"

H e l i o c e n t r i c a l l y:
Mercury6'
Venus36'
Earth59'
Marsthe same as
throughgeocentric
Plutorates

 

See also:
♦ Orbital Elements of the Planets ♦ Ephemeris
Mean Daily Motion [Munkasey M.]

The average speed of a Body's daily Sidereal motion.

See also:
♦ Orbital Elements of the Planets ♦ Ephemeris
Mean Equinox [Astro*Index]

The true equinox (or point of Aries) adjusted for the inconsistencies of nutation.

See also:
♦ True Equinox ♦ Aries ♦ Nutation
Mean Equinox [Munkasey M.]

The True Equinox (or point of Aries) adjusted forthe inconsistencies of nutation.

See also:
♦ True Equinox ♦ Aries ♦ Nutation
Mean Lunar Node [Astro*Index]

The point of intersection between the Moon's orbit and the Ecliptic, adjusted for inconsistencies in the Moon's orbit. The mean lunar node is always retrograde. It moves westward along the Ecliptic at a constant rate, making a complete circuit in 18.61 years.

See also:
♦ Retrograde Motion ♦ True Lunar Node ♦ Ecliptic
Mean Motion [DeVore]

The average motion of any body within a given period. The mean motion of a planet is based on the presumption that it moves in a circle at a uniform rate about the Sun. Actually the planets move in elliptical orbits, in portions of which this motion is accelerated and retarded in ratio to their distance from the gravi- tational center. The mean daily motions of the plants are:

Pluto0'14"         Jupiter4'59"
Neptune0'24"         Mars31'0"
Uranus0'42"         Venus36'0"
Saturn2'1"         Mercury6'0"

The Moon (around the Earth)13°10'35"
The Earth (around the Sun)59'8"

 

The Heliocentric mean motions of the planets differ from their geocentric motions.

See also:
♦ Motion ♦ Average Daily Motion ♦ Mean Orbital Speed
Mean Node [Astro*Index]

The mean (average) position of a body's True Node.

See also:
♦ True Node
Mean Orbital Speed [Astro*Index]

The mean (average) speed of a planet within its orbit.

See also:
♦ Motion ♦ Mean Motion
Mean Sidereal Day [Astro*Index]

The length of the average sidereal day, measured by two successive transits of the mean equinox over the observer's Upper Meridian. The length of the mean sidereal day is 23h56m04.09054s of mean solar time.

See also:
♦ Apparent Sidereal Day ♦ Apparent Sidereal Time ♦ Mean Sidereal Time ♦ Sidereal Day ♦ Transit ♦ Equinox ♦ Meridian ♦ Mean Solar Time
Mean Sidereal Time [Astro*Index]

Sidereal Time as determined from measurements taken in relation to the mean equinox in its successive meridian passages.

See also:
♦ Sidereal Time ♦ Equinox ♦ Meridian
Mean Sidereal Time [Munkasey M.]

The time determined from measurements taken withthe mean equinox in its successive meridian passages.

See also:
♦ Sidereal Time ♦ Equinox ♦ Meridian
Mean Solar Day [Astro*Index]

The length of the average solar day, measured by two successive transits of the mean sun over the observer's Upper Meridian. The length of the mean solar day is 24h03m56.55536 of sidereal time.

See also:
♦ Mean Solar Time ♦ Solar Day ♦ Transit ♦ Mean Sun ♦ Meridian ♦ Sidereal Time
Mean Solar Day [Munkasey M.]

The length of the average day as measured by theSun's passage. The length of the average Solar day is: 24 H 3 M 56.555 S.

See also:
♦ Mean Solar Time ♦ Solar Day ♦ Transit ♦ Mean Sun ♦ Meridian ♦ Sidereal Time
Mean Solar Time [Astro*Index]

Time measured by the motion of the Mean Sun over the observer's Upper Meridian.

See also:
♦ Mean Sun ♦ Meridian
Mean Solar Time [Munkasey M.]

The time measured from the passage of the meanequinox some fiducial or marking point or body. The apparent diurnal motion of this fiducial body relative to the mean equinox. This time is based upon the constant motion of an imaginary Sun.

See also:
♦ Mean Sun ♦ Meridian
Mean Sun [Astro*Index]

A fictitious Sun which travels once around the Earth in 24 hours. It is used to determine mean time. The mean Sun has an assigned constant angular velocity, and along the Celestial Equator, not the Ecliptic.

See also:
♦ Mean Time ♦ Angular Velocity ♦ Celestial Equator ♦ Ecliptic
Mean Sun [Munkasey M.]

A fictitous Sun which travels once around the Earth in24 hours. It is used to determine Mean Time. The Mean Sun has a fictitiously assigned constant angular velocity.

See also:
♦ Mean Time ♦ Angular Velocity ♦ Celestial Equator ♦ Ecliptic
Mean Time [Munkasey M.]

Another term for "Mean Solar Time".

See also:
♦ Mean Solar Time
Mean Time [DeVore]

A consequence of the ellipticity of the Earth's track is that its orbital motion is faster near perihelion than near aphelion. This has the effect of making the day longer in Winter than in Summer: not the day from sunrise to sunset, but from one noon to the next. We keep our clocks from going haywire by the employment of the device known as mean time, thereby measuring time not by the true Sun, as does the sundial, but by a fictitious mean Sun which moves uniformly along the celestial equator, not along the ecliptic.

See also:
♦ Mean Solar Time

 

Astro*Index Copyright © 1997 Michael Erlewine

 

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