Astronomical Facts 'N Stuff
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Astronomical Facts ‘n Stuff Mini Encyclopedia of Astronomical terms, abbreviations, objects & facts. Contents Version History ......................................................................................................................................... 2 Glossary of Astronomical & Astrophotography Terms ............................................................................... 3 Astronomy Acronyms & Abbreviations .................................................................................................. 150 Spectral Star Classes ............................................................................................................................ 159 Stellar Evolutionary Paths .................................................................................................................... 160 The Solar System .................................................................................................................................. 161 Planetary Information .......................................................................................................................... 163 Asteroids from the Main Belt ................................................................................................................ 164 Asteroids from the Kuiper Belt ............................................................................................................. 166 Modern Constellations .......................................................................................................................... 167 The Greek Alphabet .............................................................................................................................. 170 Meteor Showers .................................................................................................................................... 171 Significant People in Astronomy ........................................................................................................... 173 SI Units and Specifics ........................................................................................................................... 176 Unofficial Units and Specifics ................................................................................................................ 177 Formulas .............................................................................................................................................. 178 The Periodic Table ................................................................................................................................ 196 The Electromagnetic Spectrum ............................................................................................................. 197 Lens & Mirror Characteristics................................................................................................................ 198 4 October 2012 1 © Paul Thomas Version History Version Date Changes made 1.0.0 20 Jul 2012 Original document release 1.0.1 12 Aug 2012 Added Lens & Mirror characteristics, Electromagnetic spectrum, Solar System quick info, more terms. 1.1.0 6 Sep 2012 Added more definitions, Added more Constellation Information, Added Significant People, Changed page format to landscape. 1.2.0 30 Sep 2012 Separated Asteroids & Kuiper Belt from Solar System, Added Meteor Showers, Added Formulae, Added Planetary Info. 1.2.1 3 Oct 2012 Added more, and tidied up terms. 4 October 2012 2 © Paul Thomas Glossary of Astronomical & Astrophotography Terms ..A Abbe See “Eyepiece” Abell Cluster A galaxy cluster that belongs to the Abell catalogue. This is a listing of more than 4,000 galaxy clusters that meet certain criteria, one of which is having at least 30 galaxies within a set magnitude range. The catalogue is divided into five groups of richness according to how many galaxies the cluster contains. Class 0 clusters contain between 30 and 49 galaxies, and class 5 clusters contain more than 299 galaxies. Aberration Any optical defect and/or design error which causes any of the processed light to deviate from reaching the focal point, therefore reducing the quality of the image. Aberration of Starlight The apparent displacement of a star's position as a consequence of Earth's motion through space and the finite speed of light. Ablation The vaporisation of the surface layers of a body entering the atmosphere as a consequence of the heating that results from the compression of air ahead of it. Absolute Brightness (Absolute Magnitude) A measure of the true brightness of an object. The absolute brightness or magnitude of an object is the apparent brightness or magnitude it would have if it were located exactly 32.6 light-years (10 parsecs) away. Absolute Magnitude A scale for measuring the actual brightness of a celestial object without accounting for the distance of the object. Absolute magnitude measures how bright an object would appear if it were exactly 10 parsecs (about 33 light years) away from Earth. Absolute Zero This is the coldest temperature theoretically possible (-273.15 degrees Celsius), where the motion of atoms in a material would stop completely, leaving them only with a small amount of quantum mechanically energy. 4 October 2012 3 © Paul Thomas Absorption The process by which light transfers its energy to matter. For example, a gas cloud can absorb starlight that passes through it. After the starlight passes through the cloud, dark lines called absorption lines appear in the star’s continuous spectrum at wavelengths corresponding to the light-absorbing elements. Absorption Line A dark line in a continuous spectrum caused by absorption of light. Each chemical element emits and absorbs radiated energy at specific wavelengths, making it possible to identify the elements present in the atmosphere of a star or other celestial body by analysing which absorption lines are present. Accretion The accumulation of dust and gas onto larger bodies such as stars, planets, and moons Accretion Disk A rotating disk of gas surrounding a compact object (such as a neutron star or black hole), formed by material falling inward. Achromatic Lens A lens with two or more elements, usually of differing glass types, designed to produce an image substantially free from false colour and bringing most of the viewed colours to a sharp focus. Active Galactic Nucleus A very bright, compact region found at the centre of certain galaxies. The brightness of an active galactic nucleus is thought to come from an accretion disk around a supermassive black hole. The black hole devours matter from the accretion disk, and this in-fall of matter provides the firepower for quasars, the most luminous type of active galactic nucleus. Active Galaxy A galaxy possessing an active galactic nucleus at its centre. Actual Field of View A characteristic of eyepiece/telescope combinations. The actual field of view is the angle, measured on the sky, from one edge of the eyepiece field of view to the other. It is approximately equal to the apparent field of view divided by the magnification. Adaptive Optics or Active Optics Guiding on steroids. In most A/O units a lens is moved in real time to correct for movements in the guide star utilising refraction. This differs from traditional guiding where corrections are sent to the mount over periods of ~0.5 to 5 seconds. At long focal lengths adaptive optics can be better than normal guiding. Advanced Camera for Surveys An optical camera aboard the Hubble Space Telescope that uses CCD detectors to make images. The camera covers twice the 4 October 2012 4 © Paul Thomas area, has twice the sharpness, and is up to 10 times more efficient than the telescope’s Wide Field and Planetary Camera 2. The ACS wavelength range spans from ultraviolet to near-infrared light. The camera’s sharp eye and broader viewing area allow astronomers to study the life cycles of galaxies in the remotest regions of the universe. Aerogel An advanced material used by the Stardust spacecraft to capture small particles of cometary dust. It is 99.8 per cent air and was effective at slowing down the cometary particles gently so that they weren’t damaged. Aerosol Refers to small particles suspended in the air, as opposed to large particles like snowflakes and raindrops. Aerosols make the air look hazy by scattering light. Afocal Coupling The technique of imaging through a camera lens held up to the eyepiece of a telescope. It is used for cameras with non- removable lenses. Afterglow The fading fireball of a gamma-ray burst — a sudden burst of gamma rays from deep space — that is observable in less energetic wavelengths, such as X-ray, optical, and radio. After an initial explosion, an expanding gamma-ray burst slows and sweeps up surrounding material, generating the afterglow, which is visible for several weeks or months. The afterglow is usually extremely faint, making it difficult to locate and study. Airglow The faint background glow in the night sky caused by gas in the ionosphere. Because of airglow the night sky is never completely dark as seen from Earth's surface. Airy Disk The Airy disk is the brightest spot formed by a star image as seen through a telescope. It is surrounded by alternating rings of light and dark (these are due to diffraction - any light passing through an aperture is diffracted, and the effect is inversely proportional to the size of the aperture.) An optical system of good quality increases the relative brightness of the central Airy disk compared to the surrounding diffraction rings.