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This Abbreviated as '''“AU,”''' it is the mean distance from the [[Earth ]] to the [[Sol|Sun, i.e. ]] 149,597,870 km871 kilometers (92,955,807. (approx 93 million 3 miles);.
A Abbreviated as '''“pc,”''' it is a unit for expressing of measurement used to express large distancesto [[Astronomical Terms Database#Astronomical Object|astronomical objects]] beyond [[Earth|Earth’s]] [[Sol system|Solar System. ]] It is the distance at which a [[Star|star ]] would have a [[Astronomical Terms Database#Parallax|parallax ]] of one arc second, equal to 3.2616 26163344 [[Light year|light years, ]] 206,265 264.806 [[Astronomical Terms Database#Astronomical Unit|astronomical units ,]] or 30,856,775,800,000 kilometers (AU19,173,511,600,000 miles) or 30.857 * 10E12 km.Penumbra:
A Also referred to as “multiple star system,” it is a set of a few [[Gravity|gravitationally]] bound stellar objects , such as [[Star|stars,]] that [[Orbit|orbit]] each other. A set of many such stellar objects , or [[Star|stars,]] is a [[Astronomical Terms Database#Star Cluster|star cluster. ]] See "also [[Astronomical Terms Database#Binary Star|“Binary Star Cluster," ”]] above. Compare "Planetary System," above. See also [[Star system|star system.]]; and [[Astronomical Terms Database#Planetary System|“Planetary System,”]] above.
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=== Absolute Magnitude ===
The [[Astronomical Terms Database#Apparent Magnitude|apparent magnitude ]] that a [[Star|star]] would possess if it were a distance of 10 [[Astronomical Terms Database#Parsec|parsecs ]] from [[Earth|Earth.]] In this way, absolute magnitude provides a direct comparison of the brightness of [[Star|stars.]] A [[Star|star’s]] [[Astronomical Terms Database#Luminosity|luminosity ]] and its distance from [[Earth]] provide the basis for its [[Astronomical Terms Database#Apparent Magnitude|apparent magnitude. ]] If all [[Star|stars]] were the same distance from [[Earth|Earth,]] then their [[Astronomical Terms Database#Apparent Magnitude|apparent magnitudes ]] would only be dependent on their [[Astronomical Terms Database#Luminosity|luminosities. ]] Therefore, absolute magnitudes are true indicators of the amount of [[Light|light]] each [[Star|star]] emits. The value is lower, even into the negatives, for objects that appear brighter, and higher for objects that appear dimmer. Absolute magnitude is usually measured through the visible spectrum. However, it can be measured through the entire spectrum. Absolute visual magnitude, through the visible spectrum, is abbreviated as '''''Mv.''''' Compare "[[Astronomical Terms Database#Apparent Magnitude|“Apparent Magnitude," ”]] below.
=== Accretion ===
=== Apparent Magnitude ===
A measure of how bright an [[Astronomical Terms Database#Astronomical Object|astronomical object, ]] as viewed from [[Earth|Earth,]] appears to be to the naked [[Human]] eye, but calculated to a value that negates any interference from [[Earth|Earth's]] atmosphere. The value is lower, even into the negatives, for objects that appear brighter, and higher for objects that appear dimmer. Unless otherwise indicated, apparent magnitude is usually measured through the visible spectrum. However, it can be measured through specific wavelengths, such as near infra-red. Apparent magnitude is abbreviated as '''''m.''''' Compare "[[Astronomical Terms Database#Absolute Magnitude|“Absolute Magnitude," ”]] above.
=== Arc Minute ===
=== Astronomical Object ===
Naturally occurring structures that exist in observable [[Space|space.]] [[Asteroid|Asteroids,]] [[Moon|moons,]] [[Planet|planets,]] and [[Star|stars]] are examples of single astronomical objects. [[Nebula|Nebulae,]] [[Astronomical Terms Database#Star systemSystem|star systems,]] [[Astronomical Terms Database#Star Cluster|star clusters, ]] and [[Galaxy|galaxies]] are examples of compound astronomical objects.
=== Astronomical Unit ===
=== Aurora ===
=== Binary Star ===
A system of two stars orbiting around a common centre of mass due to their mutual gravity. Binary stars are twins in the sense that they formed together out of the same interstellar cloud. Compare [[Astronomical Terms Database#Star System|“Star System,”]] below.
=== Blue Moon ===
=== Luminosity ===
Absolute brightness. The total energy radiated into [[Space|space, ]] per second, by a celestial an [[Astronomical Terms Database#Astronomical Object|astronomical object ,]] such as a [[Star|star.]] Compare [[Astronomical Terms Database#Absolute Magnitude|“Absolute Magnitude,”]] above.
=== Lunation ===
=== Moon ===
A naturally occurring satellite, or relatively large body, orbiting a planet.
=== Multiple Star System ===
See [[Astronomical Terms Database#Star System|“Star System,”]] below.
=== Parsec ===
=== Penumbra ===
Means, literally, "dim light". It most often refers to the outer shadow cast during eclipses, and defines the region of shadow which gives rise to a partial eclipse. It is also the lighter area surrounding the central region of a sunspot.
=== Star Cluster ===
A loose association of [[Star|stars ]] within the the [[Milky WayGalaxy|Milky Way Galaxy. ]] Examples are include the Pleiades (, also known as the Seven Sisters) , the Hyades clusters, and the Beehive Clusters, each visible from [[Earth|Earth,]] to the naked [[Human]] eye.
=== Star System ===
=== Sunspot ===
