Beginning Astrophotographer Terms
This a list some of the more common celestial terms and objects that you may wish to learn how to find, look at with your telescope and eventually create an image for.
Asterism -is a clear, recognizable pattern or a shape found in the sky that is formed by a group of stars that is smaller in area than a constellation.
Comet – is a small celestial body composed of ice and dust and can be found orbiting the Sun on an elongated path. When a comet’s orbit is closere to the Sun, a long gas and dust tail is produced due to evaporating ice.
Conjunction – is the moment when two celestial objects can be found very near to each other in the night time sky.
Constellation – is any one of 88 official star patterns. Most are seen either in the summer sky or winter sky.
Double Star – is when two stars appear close together in the sky. Some are just chance alignments as seen from Earth, Others are binary systems where stars will orbit each other.
Galaxy – is a huge collection or gathering of stars, gas,and dust that gravity binds together.. Galaxies are categorized by their shape: spirals, barred spirals, and ellipticals. About 75% of the brighter galaxies we see in the night sky are are spirals.
Globular Star Cluster – is a tightly-packed spherical cluster that may have up to a million older stars. Globular clusters are found in a halo that surrounds the Milky Way Galaxy.
Light-year – is the measurement term used to describe the distance that light travels in one year. One light- year is equal to six trillion miles. With the vastness of the known universe, distances to celestial objects are measured in light-years.
Lunar Eclipse – is when the Earth’s shadow crosses the face of the Moon. This causes the Moon togradually darken, and then lighten over the course of an hour or two. A partial lunar eclipse is when due to the location part of the moon is covered by the Earth’s shadow. This can be seen with the naked eye.
Magnitude – is a number used to describe the level of brightness of a each star giving a way to measure the relative brightness. A first magnitude star is the brightest category and is about two and a half times brighter than a second magnitude star. About 20 stars are considered first magnitude . Human eye can typically see stars as faint as sixth magnitude without a telescope
Messier Object List – is a master list of 110 star clusters, nebulas, and galaxies that were compiled by Charles Messier , who was an 18th century comet-hunter. On star maps, you will find they are specified by the letter “M” followed by the object number. For example, the Orion Nebula would be listed as M42.
Meteor – is a bright streak of light in the sky that is produced by a piece of debris called a “meteoroid.” Traveling at a high rate of speed, it will burn up as it enters Earth’s atmosphere Meteors are commonly referred to as “shooting stars,” even though they are not even close to being a star.
The Moon – is 239,000 miles from Earth and is its only natural satellite. The Moon revolves around the Earth every 27.3 days and since it also rotates once every 27.3 days, we never see its far side. The Moon’s phases are based on its location relative to the Earth and the Sun.
Nebula – is a cloud of gas or dust in space. “Reflection” nebulas, are those where starlight reflects off the nebula’s dust.. “Emission” nebulas, are where the cloud itself emits light because its atoms are affected by a lot of nearby hot stars. Nebulas are essentially giant star-forming factories.
NGC Object List – is the “New General Catalog.” which is a list of deep sky objects first published in 1888 For the most part, NGC celestial objects are fainter than the Messier objects.
Open Star Cluster – is a group of a few hundred stars, bound together by gravity, and moving through space together. Open star clusters are generally found closer to Earth than the globular clusters. These stars are considered to be much younger.
Opposition – is the point in a planet’s orbit when it appears to be opposite the Sun. When a planet is in its opposition point, it can be seen in the night sky from dusk till dawn.
Planetary Nebula – is a shell of gas that late in the life of a star will be puffed off by the star life. It sometimes looks like a ring, as if the gas is wrapped around a central star.
The Planets – According to the International Astronomical Union the definition is a spherical object orbiting the Sun with sufficient mass to have its own gravity, and a clear neighborhood around its orbit. There are 8 planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is now considered a “dwarf planet.” Other dwarf planets include a newly discovered object called “Eris” found in the Kuiper Belt beyond Pluto and a former asteroid called “Ceres.”
Solar Eclipse – is a rare celestial event that happens whenever a New Moon passes directly between the Sun and the Earth. Solar eclipses can be total or partial. Total eclipses occur when the Moon covers the entire disk of the Sun. These should not be observed with the naked eye.
Stars – are enormous spheres of hot gas when hydrogen gas is fused to form helium. This is what generates light and energy deep within their cores. The temperature of a star varies with its color. Blue-white stars are the hottest, yellow-orange stars are moderately-hot, while red stars are the coolest. The closest star to Earth is our Sun( 93,000,000 miles) which is a moderately-hot yellow- orange star, whose surface temperature is about 11,000°F. The next closest star is over 4 light-years away, and.is called Alpha Centauri.
Sunspots – are dark, highly magnetized blemishes on the surface of the Sun,they are in reality cooler areas, about 1,500 Celsius degrees cooler than the rest of the Sun’s surface. An average sunspot is at as big as Earth. Some can grow to be up to10 times the size of the Earth.
Terminator – is the line separating sunlit reflection of day and shadow of night on the surface not the Moon or on a planet.
Transit – is an when Mercury or Venus (inner planets) passes directly in front of the Sun. With a properly filtered telescope, the planets own disk can be seen against the solar background as it transits or crosses the Sun’s disk. Transits are relatively rare occurrences.
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