






Absolute magnitude

The absolute magnitude M_{vis} of an astronomical object is the
apparent magnitude an object would have if it were placed at a distance
of 10 Parsec from the viewpoint. This magnitude is given as order of
magnitude.

Albedo

The albedo is the reflectivity of an object. The albedo represents
the ratio of reflected light to incident light.

Aphelion

The aphelion is the point in orbit where an object is the farthest
from its central body. So the aphelion is also the maximum distance
of an orbit. The opposite is the perihelion.

Apparent magnitude

Apparent magnitude m_{vis} is a measure of the brightness of a
celestial object as seen from Earth. The lower the number, the brighter
the object. This magnitude is given as order of magnitude.

Astronomical Unit (AU)

The astronomical unit is the average distance from the Earth to the Sun.
1 AU = 149.597.870,61 km = 92.960.116 miles

Diameter

A celestial bodies diameter is the distance from its surface through
the center of the body to the opposing surface, normally measured on
the equator.

Eccentricity

The eccentricity measures the relation between maximum distance a
(Aphelion) and minimum distance b (Perihelion) of an elliptical
orbit. The eccentricity measures how far from a circular shape an
elliptic orbit is.
Eccentricity e = √(a²  b²) / a.

Ecliptic

The ecliptic is the plane on which Earth moves on it orbit around the
Sun.

Escape velocity

THe minimum speed needed to allow an object of small mass (e.g. a space
probe) to escape the surface gravity of an object of larger mass is called
escape velocity.

Force of gravity

The force of gravity is the force at which a large body attracts another
object towards itself. All objects upon earth experience a force of gravity
which is directed "downward" towards the center of the earth and is
measured as 1 g = 9,78 m/s².

Inclination

The inclination of an objects orbit is the angle between the plane of
its orbit and the ecliptic for objects orbiting the Sun. The inclination
of planets satellite is the angle between the plane of its orbit and the
plane of its primary bodies equator.

Kelvin

Kelvin is based on the absolute temperature scale. The absolute temperature
minimum (0 K) is similar to 273,15 ° C in the centigrade scale.
0 K = 273,15 ° C = 460 F
0 ° C = 273,15 K = 32 F

Lightyear (ly)

The distance light travels in a year in a vacuum at the rate
of 300.000 km/s is defined as a lightyear.
1 ly = 9.460.530 × 10^{6} km = 63.239,74 AU

Oblateness

The measurement oblateness is the difference between a spheroid
and a globe. The oblateness is calculated as the difference between
polar diameter and equatorial diameter in relation to the equatorial
diameter.
Oblateness a = (d_{equ}  d_{pol}) / d_{equ}

Orbital velocity

The mean orbital velocity is the average speed of a planet or satellite
in its orbit around the central body. The orbital velocity is at its
minimum in the aphelion (maximum distance) and at its maximum in the
perihelion (minimum distance).

Order of magnitude

The order of magnitude is the degree of brightness of a celestial body.
The numerical classification 0 is reserved for the brightest stars like
Vega. A difference of five orders of magnitude represents a difference
in luminance of 100, each order of magnitude equals a multiplicator of
2,512.

Parsec (pc)

A parsec is defined as the distance from which the axis of Earth's
orbit (1 Astronomical Unit) spans an angle of an arcsecond.
1 pc = 3,261633 ly

Perihelion

The pelihelion is the point in orbit where an object is closest
to its central body. So the pelihelion is also the minimum distance
of an orbit. The opposite is the aphelion.

Rotational period

The rotational period is the time a celestial body takes to rotate
once on its axis with, respect to the stars. The rotational period is
synchronous if it is identical to the orbital period, meaning the
celestial body always shows the same side to its central body.

Rotational velocity

The rotational velocity of a planet of moon is the speed of this bodies
rotational motion around its axis. The velocity is measured as the
speed a point on the equator inherits on its rotational movement.

Sideric period

The siderial period is the period of revolution of one object (planet,
asteroid or other satellite) around its central body measured relative
to the stats. This period is measured on completion of an exactly 360°
orbit.

Spectral type

The spectral type is the classification of a star according to its
temperature as measured from the strengths of its spectral lines.
This is also the order of luminosity and mass (most luminous and most
massive to dimmest and least massive). In order of temperatures from
hottest to coolest the spectral types are O, B, A, F, G, K, M.

Synodic period

The synodic period is the time required for a planet to go from a
particular configuration as seen from Earth or respectively Sun, back
to that same configuration again.

I am most grateful for every correction or sensible improvement of
descriptions in this glossary. Please send them as EMail to
me
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