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61 Cygni wikipedia

     also called “Bessel’s Star”, is the first star whose distance was measured. It was measured using parallax by Friedrich Wilhelm Bessel. It was chosen because it had a large proper motion, suggesting it was close, and because it passes directly over the Greenwich Observatory every day, so a telescope permanently mounted vertically would be able to measure it.

Absolute magnitude wikipedia

     the brightness of a star or galaxy irrespective of distance; the magnitude a star or galaxy would appear to have from 10 parsecs away. The absolute magnitude of a planet, however, is the magnitude it would appear to have if it were one astronomical unit away from the sun, fully illuminated by the sun, and one astronomical unit from the observer. See also apparent magnitude.

Absolute zero wikipedia

     the theoretically coldest possible temperature, the temperature of a system in the lowest possible energy state. It is -273.15 degrees Celsius or -459.67 degrees Fahrenheit. The overall temperature of the universe is believed to be 2.725 degrees Celsius above absolute zero, as measured by the cosmic background radiation on the assumption that it follows the laws of black body radiation. Although negative (thermodynamic) temperatures are possible, they are actually hotter than an infinite temperature, not colder than absolute zero.

Absorption lines wikipedia

     If light passes through a diffuse gas and is then analyzed with a spectrograph, the gas will absorb certain frequencies of the light, leaving absorption lines in the spectrum. This allows one to determine the composition of the atmosphere of a star. This discovery led to the creation of the science of astrochemistry.

Achromatic wikipedia

     literally, “without color”–an achromatic telescope is one whose objective is two lenses of different material (typically a crown glass double convex lens and a flint glass plano-concave lens) in a doublet, designed to cause two colors of light, such as red and blue, to refract by equal amounts, thus reducing or eliminating chromatic aberration. See also apochromatic.

Active galactic nucleus wikipedia

     a compact region at the center of a galaxy having higher than normal radiation, likely caused by large amounts of material in an accretion disk falling into the central black hole.

Accretion disk wikipedia

     revolving matter forming a disk around a gravity source, such as a black hole. Gravity causes the matter to contract around the object, but because of conservation of angular momentum, it is hard for individual particles of the matter to get closer to the object, so it piles up in a disk.

Active optics wikipedia

     a segmented objective mirror of a large telescope with actuators (motors) that keep the mirror at its optimal shape, usually a paraboloid. See also adaptive optics

Adaptive optics wikipedia

     a segmented objective mirror of a large telescope with actuators (motors) that adjust the shape of the mirror to the current atmospheric conditions, to reduce twinkling and atmospheric distortion.

Albedo wikipedia

     the reflectivity of an object, namely the fraction of light that is reflected rather than absorbed or transmitted by the object. For example, the Earth reflects about 30% of the sunlight that shines on it, so it has an albedo of 30% or 0.3.

Algol wikipedia

     literally, “demon”, is the common name for the star Beta Persei. It was known millennia to be a variable star, and it is the first discovered case of an eclipsing binary. Its magnitude is usually 2.1 but about every two days, it dims to magnitude 3.4 for several hours. This can be detected with the naked eye.

Allen, James Van wikipedia

     an American space scientist who studied terrestrial magnetism. A satellite experiment designed by him detected the Van Allan belts in 1958.

Alpha Centauri wikipedia

     the nearest star system to the Earth and sun. It is a triple, consisting of two stars Alpha Centauri A and Alpha Centauri B orbiting each other closely 4.3 light years from Earth, and a third, Proxima Centauri, apparently orbiting the pair slowly a distance away. For the next several centuries, Proxima Centauri is the closest single star to Earth, at 4.2 light years. There is some uncertainty, and it is possible Proxima Centauri is merely passing by the system.

Alpher, Ralph Asher wikipedia

     An American cosmologist who, with George Gamow, computed the distribution of chemical elements in the first moments following the Big Bang in 1948.

Altazimuth mount wikipedia

     a simple telescope mount allowing motion along the azimuth and altitude.

Altitude wikipedia

     of an object in alt-az coordinates, is the angular distance from the horizon to the object. For example, an object at the zenith has the maximum altitude, namely 90 degrees. An object on the horizon has an altitude of 0 degrees. An object that is below the horizon (such as the sun before it rises or after it sets) has a negative altitude. The nadir has the minimum altitude of -90 degrees. Any location in the sky at any given time can be specified relative to an observer by its altitude and azimuth.

Amateur Astronomer wikipedia

     is one who studies astronomy and observes the skies as a hobby. This contrasts with a professional astronomer who observes as part of a funded program.

Andromeda Galaxy wikipedia

     is the closest non-dwarf galaxy to our own Milky Way galaxy, 2.54 million light years away. Like the Milky Way, it is a spiral galaxy. It is about twice the size and brightness as the Milky Way, but with about two-thirds the mass. It is visible to the naked eye as a hazy patch about the size of the full moon under dark skies, and was known for millennia. It is on a collision course with the Milky Way, and the two will collide in about 3 billion years, likely merging to form an elliptical galaxy. The Andromeda Galaxy, like the Milky Way, is part of the local group of galaxies.

Angstrom wikipedia

     is a unit of length equal to one tenth of a nanometer, that is one ten-billionth of a meter, or 10^-10 meters. The wavelength of visible light is from about 3500 angstroms to 7000 angstroms. An isolated hydrogen atom is about 2.4 angstroms in diameter.

Angstrom, Anders Jonas wikipedia

     was a Swedish physicist who pioneered spectroscopy applied to chemistry. The Angstrom unit of measure is named for him.

Angular distance wikipedia

     between two objects as observed from a third location, is the size of the angle whose vertex is the observer and whose sides pass through the objects. Angular distance is typically measured in degrees, minutes, seconds, or radians. Angular distance is a natural unit for measuring apparent distances between celestial objects as observed from Earth.

Angular momentum wikipedia

     a measure of rotation, proportional to mass, radius and velocity. For example, the Earth has mass 5.9742×10²⁴ kilograms. It revolves around the sun at a distance of 149598000 kilometers. It orbits at 29.8 kilometers per second. Thus, the angular momentum is the product: 2.66331055×10²³ KgKm²/s, or translating to the more usual units of kilogram-meters² per second, we divide by 1000²=1,000,000, getting 2.66331055×10¹⁷ Kgm²/s. Angular momentum, like energy, is conserved.

Annular eclipse wikipedia

     is a solar eclipse in which the moon passes directly between the sun and the Earth, but the apparent size of the moon is smaller than the apparent size of the sun so that a bright ring (annulus) appears to surround the moon.

Antisolar point wikipedia

     the apparent location in the celestial sphere exactly opposite the sun. Anticrepuscular rays appear to converge there, and under a dark sky, Gegenschein may be visible there.

Aphelion wikipedia

     The point on the elliptical orbit of an object (such as a planet) around the sun in which the object is at its farthest from the sun. One half the sum of the distance to the aphelion and the distance to the perihelion from the sun gives the mean distance of the object from the sun. See also apogee.

Apochromatic wikipedia

     literally, “away from color”–an apochromatic telescope is one whose objective is three lenses of different materials in a triplet (or sometimes more), designed to cause at least three colors of light, such as red, green, and blue, to refract by equal amounts, thus eliminating detectable chromatic aberration. See also achromatic.

Apparent magnitude wikipedia

     a measurement of stellar brightness, as the star appears from Earth. Hipparchus divided the naked-eye stars of the sky into six brightness classes, the first being the brightest, and the sixth being the dimmest. Modern astronomers turned this into a precise scale, defined so that Spica (the brightest star in the constellation Virgo) has a magnitude of 1, and for each increase in magnitude number by 1, the brightness is divided by the fifth root of 100, or about 2.51188643. Likewise, decreasing the magnitude by one multiplies the brightness by the same amount. See also Absolute Magnitude.

Apogee wikipedia

     The point on the elliptical orbit of an object (the moon or a satellite) around the Earth in which the object is at its farthest from the Earth. One half the sum of the distance to the apogee and the distance to the perigee from the Earth gives the mean distance of the object from the Earth. See also aphelion.

Archaeoastronomy wikipedia

     is the study of ancient astronomical observations and interpretations.

Asterism wikipedia

     is a pattern of stars that is not officially a constellation, such as the Big Dipper, consisting of the seven brightest stars of Ursa Major, or the Coathanger Cluster.

Asteroid wikipedia

     literally, “star like”, is a rocky body in orbit around the sun that is too small to be a planet.

Asteroid belt wikipedia

     is the main grouping of asteroids around the sun, between Mars and Jupiter.

Astrobiology wikipedia

     literally, “knowledge about star life”, is a combination of theory and the known sciences of astronomy, biology, and chemistry toward predicting the forms that life would take, how it would come about, and how and where it might be found, whether on Earth or elsewhere.

Astrochemistry wikipedia

     is the study of chemical elements in outer space, such as the composition of stars and nebulae.

Astrograph wikipedia

     is a telescope optimized toward astrophotography rather than viewing through an eyepiece. It may refer to a camera with a telescopic lens or a telescope made to accept a user’s camera.

Astrolabe wikipedia

     is a mechanical instrument for measuring the positions of naked eye objects, such as stars, the moon, and planets, for astronomy and for surveying.

Astrology wikipedia

     is a belief system predating astronomy in which astronomical events are used for fortune-telling purposes.

Astrometric binary wikipedia

     is a binary star detected by the gravitational influence of the dimmer one on the brighter one. Astronomers detect astrometric binaries by observing the path of proper motion and measuring its deviations from a straight line.

Astrometry wikipedia

     is the branch of astronomy dealing with precise measurements of the position and movement of astronomical objects.

Astronomer wikipedia

     is a person who studies astronomy or astrophysics. See also Amateur astronomer.

Astronomical unit wikipedia

     is the mean distance between the center of the Earth and the center of the Sun. It is equal to 149.6×10⁹ meters, or 0.000015813 light years or about 92,956,000 miles. It is primarily used for measurements in which meters or miles is too small and light years or parsecs is too large, particularly the distances between bodies in the solar system.

Astrophotography wikipedia

     is the photography of astronomical objects in the sky, either through a telescope or with a lone camera.

Astrophysics wikipedia

     is the study of how astronomical objects move and change.

Asymptotic giant branch wikipedia

     is the stage of a ten solar mass or less star’s evolution when it finishes burning all the helium in its core. It is like a second red giant stage. During the later part of the asymptotic giant branch, the star pulsates, becoming a pulsating variable star.

Atlas wikipedia

     a collection of maps. In astronomy, a collection of star maps. It is not named after the mythical strongman who held the world on his shoulders, but after the mythical King Atlas of Mauritania, a globe maker.

Atmosphere wikipedia

     is a layer of gas surrounding a body, such as a planet. For a star, the atmosphere is the transparent thin gas surrounding the “optically thick” (opaque) gas of the star’s photosphere.

Axis wikipedia

     In three-dimensional space, a rotating object rotates around a fixed line. This line is called the axis of the object. The axis of the Earth is the line through the north and south poles. By convention, if a body rotates about an axis, the north pole is defined to be the portion of the body intersecting the axis that appears to rotate counterclockwise if looked at from outside. The opposite intersection point is the south pole.

Azimuth wikipedia

     of an object in alt-az coordinates, is the angular distance from the direction of north to the great circle passing through the object and the zenith, measured clockwise in degrees. For example, an object to the north has an azimuth of 0 degrees, and an object to the west as an azimuth of 270 degrees. Any location in the sky at any given time can be specified relative to an observer by its altitude and azimuth.

Baade, Walter wikipedia

     first person to see individual stars in the Andromeda Galaxy. He also first proposed the existence of neutron stars.

Barred spiral galaxy wikipedia

     a spiral galaxy with an elongated bar-shaped structure at the nucleus.

Bayer designation wikipedia

     a system of naming the brightest stars in a constellation by using Greek letters (alpha, beta, gamma, and so on) invented by Johann Bayer. In most constellations, the Greek letters are assigned in order of brightness.

Bayer, Johann wikipedia

     a German astronomer, inventor of the Bayer designation for bright stars, and maker of Uranometria, the first star atlas covering the entire celestial sphere.

Benford, Gregory wikipedia

     an American astrophysicist and also a science fiction author.

Bessel, Friedrich Wilhelm wikipedia

     a German astronomer and mathematician who first computed the distance to a star, namely 61 Cygni, using parallax.

Bethe, Hans wikipedia

     an American astrophysicist who determined the processes that fuels stars.

Big Dipper wikipedia

     an asterism consisting of the seven brightest stars of Ursa Major, in the shape of a dipper.

Big bang theory wikipedia

     a model of the universe in which it formed from an extremely dense and hot state before expanding ultimately to its present size.

Binary planet wikipedia

     a planet and its moon, or two planets in orbit about each other, in which the center of gravity of the system is between them rather than inside the larger body.

Binary star wikipedia

     a pair of stars in which one orbits the other, or both orbit about a common center of gravity.

Binoculars wikipedia

     a pair of identical telescopes connected together in such a way that observation can be done with both eyes simultaneously. Usually, it refers to a hand-held device consisting of two refracting optical tubes with permanently-installed eyepieces. Binoculars were invented only a few years after the telescope was invented.

Black body radiation wikipedia

     electromagnetic radiation (light, radio waves, x-rays, and so on) emanated from a body that absorbs all light shined on it, due to its temperature. The light from a star is black body radiation, as is the glow of a red-hot stovepipe. The coolest objects emanate radio waves and microwaves. Warmer objects radiate infrared light. A hot object radiates red light, and hotter objects, yellow, orange, white, and blue-white light. Still hotter objects emanate ultraviolet light. The hottest objects known to man radiate x rays and gamma rays.

Black dwarf wikipedia

     the remnant of a dead star formed when a white dwarf radiates away all of its heat. Since the time required for a white dwarf to become a black dwarf is longer than the age of the universe, there are no black dwarfs today.

Black hole wikipedia

     an object, usually the remnant of a dead star, in which enough mass is compressed into small enough space that the gravity is too high for anything, including light, to escape. Only gravity comes out of a black hole.

Blue Moon wikipedia

     the second full moon in a month. Most months only have one full moon. The Maine Farmer’s Almanac had monthly calendars with the phases of the moon shown. The first full moon was drawn in red, but the second one, in blue.

Blue giant wikipedia

     a young, massive star that burns so hot it visibly radiates blue light (see black body radiation). Because of its mass and temperature, it is also a giant star, even while on the main sequence.

Blue straggler wikipedia

     a blue star in a globular cluster that should be too old to have any surviving blue stars. Likely, they are the result of two older stars colliding and merging, producing a newly-reignited larger star.

Bode’s law wikipedia

     a hypothesis that the mean distances of the planets from the sun follow a pattern. Assign a number n to each planet using the sequence 0 for Mercury, 3 for Venus, and so on in order: 6, 12, 24, 48, etc., with each number after 3 being twice the previous number. Then, the mean distance of the planet from the sun is about (n+4)/10 astronomical units. It was later discredited by the discovery of Neptune and Pluto, and the fact that there is no planet between Mars and Jupiter.

Bode, Johann Elert wikipedia

     a German astronomer who popularized Bode’s Law, discovered Bode’s Galaxy (Messier 81), and computed the orbit of Uranus.

Bohr, Niels wikipedia

     a Danish physicist who invented a model of the atom that explained spectral lines and contributed to the subject of quantum mechanics.

Bok globule wikipedia

     a cold, dark, dense molecular gas cloud in which star formation takes place.

Brahe, Tycho wikipedia

     a Danish astronomer known for his accurate observations, enabling later astronomers to deduce laws of motion and gravity.

Brown dwarf wikipedia

     a gasseous object too small to burn ordinary hydrogen to produce helium, but large enough to burn deuterium, a less-common isotope of hydrogen. A brown dwarf has mass between 13 times the mass of Jupiter and 80 times the mass of Jupiter.

CCD camera wikipedia

     a camera that uses a charge coupled device–a chip which converts light signals to electricity more efficiently than photographic film, especially with faint light, making them useful for astronomy.

CMOS camera wikipedia

     a camera that uses a complementary metal-oxide semiconductor integrated circuit to convert light signals to electricity. It is much cheaper than a CCD camera, and is thus used in many consumer digital cameras. They are less sensitive and produce more noise, but also have smaller lag time and consume less power than CCDs.

Caldwell catalog wikipedia

     a catalog of 109 deep sky objects suitable for small telescopes compiled by Patrick Caldwell-Moore, intended to complement the Messier catalog.

Calendar wikipedia

     a system for naming and keeping track of days.

Camera wikipedia

     short for “Camera Obscura”, meaning “dark chamber”, is a device for recording images.

Cannon, Annie Jump wikipedia

     along with Edward Pickering, created the modern star classification scheme, classifying the stars as type O, B, A, F, G, K, or M according to their surface temperature or equivalently, color.

Carbon star wikipedia

     a type of red giant or red dwarf star whose atmosphere contains more carbon than oxygen. This gives the star a very strong red color.

Carbonaceous chondrite wikipedia

     a type of stony meteorite that has not been affected by melting and contains water and organic compounds.

Cassegrain wikipedia

     a reflector telescope in which the primary mirror has a hole in it for observing through, while the secondary mirror is parallel to the primary mirror, directing reflected light back toward the hole. This means the tube can be shorter than in a Newtonian reflector.

Cassini division wikipedia

     the most prominent gap in the rings of Saturn.

Cassini, Giovanni Domenico wikipedia

     a French astronomer who discovered Jupiter’s great red spot, four of Saturn’s moons, and the Cassini division in Saturn’s rings.

Catadioptric wikipedia

     a telescope using both lenses (in addition to the eyepiece) and mirrors to allow fast (small) focal ratios without increasing problems like coma and astigmatism.

Celestial mechanics wikipedia

     a branch of astronomy dealing with motion and gravity in the universe.

Cephied variable wikipedia

     a type of pulsating variable star notable for a tight correlation between its period and luminosity, allowing it to be used to estimate distances.

Ceres wikipedia

     the largest asteroid, and the first one discovered. It is one of only four asteroids large enough to be pulled into a spherical shape by its gravity.

Chandrasekhar, Subrahamanyan wikipedia

     an American astrophysicist who use Einstein’s theory of general relativity to deduce the existence of black holes.

Chaos wikipedia

     loosely, “unpredictability”, is a branch of mathematics dealing with system in which simple principles lead to complex behavior. More specifically, a system is considered chaotic if small perturbations of initial conditions result in large changes in behavior. The only way to predict the evolution of a chaotic system is to simulate it very precisely. With some systems, such as with predicting the weather a few weeks from now, it is not possible with existing technology.

Chromatic aberration wikipedia

     color changes in an image produced by a lens having a different refractive index for different colors of light. Isaac Newton invented the Newtonian reflector telescope, which uses a mirror instead of a lens, to eliminate chromatic aberration. Apochromatic and achromatic telescopes are refractors that are designed to reduce chromatic aberration.

Cluster wikipedia

     a group of objects bound by gravity, such as a star cluster or a galaxy cluster.

Collimation wikipedia

     collimated light is light whose rays are parallel. A telescope is collimated if its optics are aligned properly so that collimated light going in is collimated coming out. Poorly-collimated optics means stars will not focus to a sharp point.

Comet wikipedia

     an icy solar system body that passes close enough to the sun to partially vaporize and gain a temporary atmosphere. The solar wind typically blows the atmosphere into a tail pointing away from the sun.

Conjunction wikipedia

     a solar system object, such as a planet, is in conjunction with another object (usually the sun) if both appear in approximately the same place in the sky. Mercury or Venus is in conjunction it is at its closest point to Earth (inferior conjunction) or its farthest point from earth (superior conjunction).

Constellation wikipedia

     an area of the sky, generally containing a pattern of stars, officially recognized by the International Astronomical Union to aid in locating objects in the sky. It is the stellar equivalent of countries or states.

Coordinates wikipedia

     a system for assigning numbers to a point (on a sphere or plane, in a space, or in a more general manifold) to uniquely identify that point. For example, celestial coordinates (right Ascension and declination) are used to specify positions of stars and other objects in the sky.

Copernicus, Nicolaus wikipedia

     a Polish astronomer who was the first to propose a heliocentric model of the solar system.

Corona wikipedia

     literally “crown”, is the atmosphere of the sun, visible only during a total solar eclipse.

Coronagraph wikipedia

     a precise clock–a device for measuring time accurately, originally invented for navigation on the ocean: to determine one’s longitude using a sextant or astrolabe, one must measure the altitude and azimuth of several stars, and one must know the exact time.

Cosmic background radiation wikipedia

     is a 2.725 kelvin (2.725 Celsius degrees above absolute zero) black body radiation with a peak at wavelength 1.9 millimeters that pervades the universe. It probably is leftover from the big bang.

Cosmic rays wikipedia

     radiation from space, mostly protons. Some of it comes from the sun, some from other stars, and some from other galaxies. Supernovas produce a significant fraction of cosmic rays.

Cosmic string wikipedia

     a hypothetical 1-dimensional topological defect in spacetime. If they exist, they are about the diameter of a proton but very dense and with lots of gravity.

Cosmological principle wikipedia

     roughly speaking, states that the laws of physics are the same at any place, at any time, in the universe. More precisely, the universe is homogeneous (the same everywhere) and isotropic (the same in all directions) on the large scale.

Cosmology wikipedia

     literally “reasoning about the order of things”, is the mathematical study of the universe as a whole and its history and future.

Cosmos wikipedia

     a synonym of “universe“–the spacetime in which we live, as well as everything in it.

Crab Nebula wikipedia

     is the first object in Messier’s catalog. It is a remnant of a supernova that was observed in 1054. It contains the Crab Pulsar, left over from the supernova, which is the first neutron star discovered. The crab nebula is the first supernova remnant discovered.

Crater wikipedia

     a depression on the surface of a rocky body, usually caused by impact by a smaller body, or less commonly in the solar system but more commonly on Earth, by a volcano.

Crepuscular rays wikipedia

     or “sun rays” or “God’s rays”, are visible rays of scattered sunlight, often streaming through gaps in clouds. They are most prominent near sunrise and sunset.

Crescent wikipedia

     the stereotypical “moon shape”–a shape enclosed by two circular arcs of different diameters, joined at their endpoints, both no more than half of a circle, that are concave in the same direction.

Crosshair wikipedia

     also called a “reticle”, is a cross shape superimposed on an image through an optical device (such as a telescope) to make centering and measurements easier.

Culmination wikipedia

     of a celestial object, is the time that it appears at its highest point in the sky, on the meridian.

Dark energy wikipedia

     is a hypothetical form of energy permeating space, postulated to explain accelerating expansion of the universe. Theories that include dark energy predict it makes up three-fourths of all the mass and energy of the universe, with dark matter making up most of the rest.

Dark matter wikipedia

     is a form of matter of unknown composition that interacts with visible matter only through gravity. Its presence is inferred by its gravitational effect on visible matter, particularly through rotation velocities of galaxies and velocities of galaxies in

Dark nebula wikipedia

     a cold molecular cloud that obscures light. A dark nebula can only be seen if it eclipses bright objects behind it. The most well-known dark nebulae include the coal sacks in the southern Milky Way and the Horsehead nebula in Orion. Bok globules are examples of dark nebulae.

Day wikipedia

     the mean time between two successive sunrises, equal to 24 hours on Earth. This is about four minutes longer than the rotational period of the Earth (called a sidereal day) because of the Earth’s revolution around the sun.

De Sitter, Willem wikipedia

     a Dutch astronomer who, along with Albert Einstein, wrote a paper in 1932 postulating the existence of dark matter.

Declination wikipedia

     of an object in celestial coordinates, is the angular distance between the object and the north celestial pole. Declination and Right ascension together uniquely specify the location of an object in the sky relative to the stars and constellations.

Deep sky wikipedia

     a deep sky object is any object that is neither a single star nor a member of the solar system. Deep sky objects include nebulae, galaxies, and star clusters.

Deep sky camera wikipedia

     a camera, usually with a CCD, that is ultra-sensitive to faint light to facilitate recording deep sky objects.

Deep space wikipedia

     with regard to space exploration, is space beyond the orbit of Earth about the sun.

Diagonal wikipedia

     see star diagonal.

Diameter wikipedia

     of an object is the longest distance between two locations on the object.

Differential rotation wikipedia

     the situation where different parts of a rotation object have different angular velocities. For example, the sun exhibits differential rotation, which showed it was gasseous.

Diffuse nebula wikipedia

     any nebula thin enough that it does not absorb most of the light shined on it. A diffuse nebula can be a reflection nebula, emission nebula, or a supernova remnant.

Digital single-lens reflex camera wikipedia

     or DSLR camera, is a digital camera (usually using a CMOS or CCD) that uses a mirror to reflect the image entering the lens through the viewfinder, allowing the user to focus the camera by looking through the viewfinder. When the shutter button is pressed, the mirror is moved out of the way so that the exposure can be taken.

Digitized Sky Survey wikipedia

     a digital photographic atlas of the night sky.

Distance modulus wikipedia

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Doppler effect wikipedia

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Double star wikipedia

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Doublet wikipedia

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Drake, Frank wikipedia

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Dust wikipedia

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Dwarf Galaxy wikipedia

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Earth wikipedia

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Einstein, Albert wikipedia

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Elliptical Galaxy wikipedia

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Encke, Johann Franz wikipedia

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Energy wikipedia

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Full moon wikipedia

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Galactic Cluster wikipedia

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Galaxy wikipedia

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Galaxy Cluster wikipedia

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Galilean moon wikipedia

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Galilei, Galileo wikipedia

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Galileo wikipedia

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Gamow, George wikipedia

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Gas wikipedia

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Gas giant wikipedia

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Gravity wikipedia

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Greenwich Observatory wikipedia

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Hawking, Stephen wikipedia

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Hevelius, Johannes wikipedia

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Hipparchic cycle wikipedia

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Hipparchus wikipedia

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Honeycomb mirror wikipedia

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Horizon wikipedia

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Hot Jupiter wikipedia

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Hour wikipedia

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Hoyle, Fred wikipedia

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Hubble Classification wikipedia

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Hubble Space Telescope wikipedia

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Hubble sequence wikipedia

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Hubble, Edwin Powell wikipedia

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Huygens, Christiaan wikipedia

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Hydrogen wikipedia

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Hyperbola wikipedia

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Ice wikipedia

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Ice giant wikipedia

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Index Catalog wikipedia

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Interacting galaxies wikipedia

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Interferometer wikipedia

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Interferometer wikipedia

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Interstellar cloud wikipedia

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Iron wikipedia

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Irregular Galaxy wikipedia

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Jan Oort wikipedia

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Julian day wikipedia

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Jupiter wikipedia

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Jupiter mass wikipedia

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Keck observatory wikipedia

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Kellner wikipedia

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Kepler’s laws wikipedia

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Kepler, Johannes wikipedia

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Keyhole problem wikipedia

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Kip Thorne wikipedia

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Kitt Peak National Observatory wikipedia

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Kuiper, Gerard wikipedia

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LaCaille, Nicolas Louis de wikipedia

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Lagrange, Joseph-Louis wikipedia

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Lagrangian points wikipedia

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Langley, Samuel Pierpont wikipedia

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Laplace, Pierre-Simon wikipedia

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Large Binocular Telescope wikipedia

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Laser pointer wikipedia

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Lassell, William wikipedia

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Last quarter wikipedia

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Latitude wikipedia

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Lens wikipedia

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Lens sag wikipedia

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Lenticular galaxies wikipedia

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Levy, David wikipedia

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Lick telescope, James wikipedia

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Light pollution filter wikipedia

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Light year wikipedia

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Limb wikipedia

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Lines of force wikipedia

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Liquid mirror wikipedia

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Little Dipper wikipedia

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Local bubble wikipedia

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Local group wikipedia

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Local supercluster wikipedia

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Longitude wikipedia

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Lowell, Percival wikipedia

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Luminosity distance wikipedia

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Lunar eclipse wikipedia

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Lunar mass wikipedia

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Maanen, Adriaan van wikipedia

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Magnetar wikipedia

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Magnetic field wikipedia

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Magnitude wikipedia

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Main Sequence wikipedia

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Major axis wikipedia

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Maksutov wikipedia

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Mare wikipedia

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Mars wikipedia

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Mascon wikipedia

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Maser wikipedia

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Mass spectrometry wikipedia

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Matter wikipedia

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Mauna Key Observatory wikipedia

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Maxwell, James Clerk wikipedia

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May, Brian wikipedia

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Mercator projection wikipedia

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Mercury wikipedia

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Meridian wikipedia

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Messier Catalog wikipedia

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Messier, Charles wikipedia

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Metal wikipedia

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Meteor wikipedia

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Meteor shower wikipedia

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Meteorite wikipedia

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Meteoroid wikipedia

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Metonic cycle wikipedia

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Milky Way wikipedia

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Minkowski, Rudolph wikipedia

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Minor axis wikipedia

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Minor planet wikipedia

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Minute wikipedia

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Mira wikipedia

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Mira variable wikipedia

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Mobius, August Ferdinand wikipedia

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Molecular cloud wikipedia

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Momentum wikipedia

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Monocular wikipedia

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Month wikipedia

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Moon wikipedia

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Moon filter wikipedia

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Moore, Patrick wikipedia

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Mount wikipedia

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Multiple star wikipedia

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NASA wikipedia

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NGC wikipedia

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Nadir wikipedia

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Nagler wikipedia

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Nebula wikipedia

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Nebula filter wikipedia

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Nemesis wikipedia

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Neptune wikipedia

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Neutrino wikipedia

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Neutron star wikipedia

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New General Catalog wikipedia

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New moon wikipedia

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Newton’s laws wikipedia

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Newton, Isaac wikipedia

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Newtonian wikipedia

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Node wikipedia

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North Star wikipedia

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Nova wikipedia

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Nutation wikipedia

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Objective wikipedia

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Observational Astronomy wikipedia

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Observatory wikipedia

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Occult wikipedia

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Oceanus wikipedia

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Octant wikipedia

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Oort cloud wikipedia

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Open Cluster wikipedia

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Opposition wikipedia

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Optical double wikipedia

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Optical tube assembly wikipedia

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Orange giant wikipedia

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Orbit wikipedia

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Orbital velocity wikipedia

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Order of magnitude wikipedia

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Orrery wikipedia

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Parabola wikipedia

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Parallax wikipedia

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Parsec wikipedia

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Peculiar galaxy wikipedia

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Penrose, Roger wikipedia

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Penumbra wikipedia

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Perihelion wikipedia

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Perigee wikipedia

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Period wikipedia

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Phase wikipedia

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Photomultiplier tube wikipedia

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Pickering, Edward Charles wikipedia

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Pickering, William Henry wikipedia

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Plait, Philip wikipedia

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Planet wikipedia

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Planetarium wikipedia

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Planetary camera wikipedia

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Planetary filter wikipedia

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Planetary nebula wikipedia

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Planetesimal wikipedia

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Planetoid wikipedia

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Plasma wikipedia

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Plossl wikipedia

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Pluto wikipedia

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Polar alignment wikipedia

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Polar cap wikipedia

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Polar projection wikipedia

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Pole wikipedia

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Pole star wikipedia

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Position angle wikipedia

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Power wikipedia

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Precession wikipedia

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Preon star wikipedia

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Primary mirror wikipedia

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Prime meridian wikipedia

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Proper motion wikipedia

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Protogalaxy wikipedia

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Protoplanetary disk wikipedia

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Protostar wikipedia

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Proxima Centauri wikipedia

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Ptolemy wikipedia

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Pulsar wikipedia

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Pulsating variable wikipedia

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Pythagoras wikipedia

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Quadrant wikipedia

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Quadrature wikipedia

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Quark star wikipedia

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Quarter moon wikipedia

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Radial velocity wikipedia

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Radio Astronomy wikipedia

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Radius wikipedia

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Red dwarf wikipedia

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Red giant wikipedia

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Redshift wikipedia

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Reflector wikipedia

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Refractor wikipedia

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Relativity wikipedia

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Right ascension wikipedia

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Ring Galaxy wikipedia

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Rings wikipedia

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Ritchey, George Willis wikipedia

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Ritchey-Chretien wikipedia

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Rocky planet wikipedia

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Russell, Henry Norris wikipedia

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SETI wikipedia

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SLR camera wikipedia

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Sagan, Carl wikipedia

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Saros cycle wikipedia

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Satellite wikipedia

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Saturn wikipedia

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Schmidt wikipedia

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Schmidt camera wikipedia

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Schwarzschild, Karl wikipedia

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Second wikipedia

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Secondary mirror wikipedia

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Secular phenomena wikipedia

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Seeing wikipedia

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Semi-major axis wikipedia

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Semi-minor axis wikipedia

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Setting circles wikipedia

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Sextant wikipedia

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Seyfert, Carl Keenan wikipedia

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Shapley, Harlow wikipedia

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Shepherd moon wikipedia

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Sidereal time wikipedia

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Sinus wikipedia

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Sirius B wikipedia

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Solar day wikipedia

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Solar eclipse wikipedia

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Solar filter wikipedia

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Solar flare wikipedia

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Solar luminosity wikipedia

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Solar mass wikipedia

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Solar radius wikipedia

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Solar system wikipedia

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Solar wind wikipedia

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Solstice wikipedia

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Space-time wikipedia

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Special Relativity wikipedia

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Spectral type wikipedia

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Spectrograph wikipedia

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Spectrum wikipedia

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Spectrum binary wikipedia

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Speed of light wikipedia

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Sphere wikipedia

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Spherical Aberration wikipedia

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Spicule wikipedia

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Spiral Galaxy wikipedia

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Spiral arm wikipedia

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Spitzer, Lyman wikipedia

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Spotting scope wikipedia

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Star wikipedia

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Star Cluster wikipedia

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Star cloud wikipedia

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Star diagonal wikipedia

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Starburst galaxy wikipedia

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Starspot wikipedia

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Steady state theory wikipedia

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Stellar nursery wikipedia

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Stellar wind wikipedia

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Subaru wikipedia

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Substellar object wikipedia

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Sun wikipedia

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Sunspot wikipedia

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Superbubble wikipedia

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Supercluster wikipedia

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Supergiant wikipedia

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Supernova wikipedia

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Supernova remnant wikipedia

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Surface area wikipedia

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Surface brightness wikipedia

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Surface temperature wikipedia

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Synodic day wikipedia

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Syzgy wikipedia

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Telescope wikipedia

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Telrad wikipedia

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Temperature wikipedia

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Terra wikipedia

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Terrestrial planet wikipedia

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Tide wikipedia

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Time wikipedia

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Titan wikipedia

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Tombaugh, Clyde W. wikipedia

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Torque wikipedia

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Transparency wikipedia

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Triplet wikipedia

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Tripod wikipedia

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Trojan points wikipedia

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Trojans wikipedia

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Tropic wikipedia

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Tropical year wikipedia

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Trumpler, Robert Julius wikipedia

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Twilight wikipedia

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Tycho wikipedia

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Umbra wikipedia

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Unity finder wikipedia

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Universal gravitation wikipedia

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Universe wikipedia

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Uranography wikipedia

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Uranus wikipedia

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Van Allen, James wikipedia

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Van Allen Belts wikipedia

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Variable star wikipedia

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Venus wikipedia

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Virgo A Cluster wikipedia

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Virgo Supercluster wikipedia

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Visible spectrum wikipedia

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Visual binary wikipedia

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Volume wikipedia

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Vulcan wikipedia

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Vulcanoid wikipedia

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Waning wikipedia

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Water wikipedia

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Waxing wikipedia

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Webb telescope wikipedia

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Webb, Thomas William wikipedia

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Week wikipedia

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Wheeler, John Archibald wikipedia

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White dwarf wikipedia

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White giant wikipedia

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White hole wikipedia

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William Herschel Telescope wikipedia

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Year wikipedia

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Yellow dwarf wikipedia

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Yerkes observatory wikipedia

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Zenith wikipedia

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Zodiac wikipedia

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Zodiacal light wikipedia

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