Common Astronomical Terms

Common Astronomical Terms – A Brief Glossary

1. Alt-Azimuth mount – a simple two-axis mount for supporting and rotating a scope about two upright axes.
2. Aperture – the size of the primary optical surface of a telescope.
3. Aphelion – the point when/where an object orbiting the sun is furthest from the sun.
4. Astronomical Unit (AU) – approximately equal to the mean Earth-Sun distance – 150,000,000 km.
5. Astrophotography – a specific type of photography used to capture images of astronomical objects.
6. Cassegrain Telescope – often used as a broad term to define telescopes fitting into the catadioptric class.
7. Collimation – the alignment of optical components within a device such as a telescope.
8. Coma – A comet’s atmosphere – composed of dust or various gases surrounding its nucleus.
9. Comet – a celestial body orbiting the sun.
10. Declination – can be seen as ‘the latitude on the earth projected onto the sky’.
11. Dobsonian (Dob) Telescope – a design popularized by the amateur astronomer John Dobson.
12. Earthshine – the light of the sun as reflected back into space by the earth – illuminates the moon.
13. Eyepiece – also known as the ocular – magnifies an image.
14. Field of View – the amount of sky that can be seen through a telescope’s eyepiece.
15. Focal Length – distance from where light enters a telescope to the point where the image is focused.
16. German Equatorial Mount – a mount for telescopes - that follows the rotation of the sky (the celestial sphere).
17. Heliocentric – relating to the sun as the central point of an orbit.
18. Light Pollution – stray light – as from urban areas – which greatly reduce observation opportunities.
19. Magnification – relationship between the telescope’s and eyepieces’ focal lengths.
20. Magnitude – unit(s) used to describe the brightness of astronomical objects.  
21. Meteoroid – body drifting in space with enough mass to be detected but smaller than an asteroid.
22. Meteors – small rocky or icy particles swept up by the earth in its orbit of the sun – shooting stars.
23. Newtonian Telescope – a reflecting telescope in which light is reflected via a series of mirrors to an eyepiece.
24. Orbit – the path of one object about another – as an object orbiting the sun.
25. Parabolic Mirror – shaped in an exact curve, to permit received light to be focused at the same point.
26. Perigee – point where and when an object’s orbit is closest to the earth (as opposed to the sun).
27. Perihelion - point where and when an object’s orbit is closest to the sun.
28. Pulsars – highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation.
29. Quasar – a very energetic and distant galaxy; the most luminous objects in the universe.
30. Reflector – a telescope that uses a mirror as its primary element.
31. Refractor – A telescope that uses a lens as its primary element.
32. Satellite – any object that orbits another celestial body.
33. Schmidt-Cassegrain Telescope (SCT) - a telescope that uses a combination of mirrors and lenses.
34. Supernova – (plural – supernovae) a stellar explosion – more energetic than a nova.
35. Zenith – the position directly overhead.

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Refs:

Common Telescope Terms          Telescope Advice http://www.telescopeadvice.com/common-terms.htm

Moon Glossary: Lunar Terms and Definitions                           moonconnestion.com          http://www.moonconnection.com/moon-glossary

Glossary of astronomical Terms International Comet Quarterly                              http://www.cfa.harvard.edu/icq/ICQGlossary.html