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Astronomy Reference Libraries

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Extraterrestrial Life
2004-10-19 04:45:41

Extraterrestrial Life -- Extraterrestrial life is life beyond planet Earth (apart from humans travelling in space, and living organisms they bring along or send). There are many questions about extraterrestrial life, including: -- Does it exist? -- Where? -- What kind? -- Could there be non-carbon based life forms, e.g. life forms based on other elements like silicon (See Carbon...

Event Horizon
2004-10-19 04:45:41

Event Horizon -- The event horizon is a boundary beyond which information will never reach an observer. An event horizon is a mathematical construct and not a physical object and a person passing through an event horizon will not notice any odd behavior. From an outside observer however, an object passing though an event horizon will appear redder and dimmer and will appear to freeze at the...

Emission Nebula
2004-10-19 04:45:41

Emission Nebula -- In astronomy, emission nebulae are clouds of ionized gas, emitting light of various colors. The most common source for ionization are high-energy photons emitted from a nearby young, hot star. Usually, a young star will ionize part of the same cloud from which it was born. Only big, hot stars can release the amount of energy required to ionize a significant part of a...

Elliptical Galaxy
2004-10-19 04:45:41

Elliptical Galaxy -- In astronomy, one of the main classes of galaxy in the Hubble classification and characterized by a featureless elliptical profile. Unlike spiral galaxies, elliptical galaxies have very little gas or dust and no stars have recently formed within them. They range greatly in size from giant ellipticals, which are often found at the centres of clusters of galaxies and...

Ecliptic
2004-10-19 04:45:41

Ecliptic -- The ecliptic is the geometric plane that contains the orbit of the Earth. The orbits of most planets in the Solar System lie very close to it. Seen from the Earth, this is the great circle on the celestial sphere that contains the different positions of the Sun relative to the background stars throughout the year, and most planets can be seen close this circle. The zodiac...

Eclipse
2004-10-19 04:45:41

Eclipse -- An eclipse occurs when an astronomical body such as a planet, or satellite gets between a source of light (e.g. the Sun) and another body. For instance, Jupiter eclipses its moons when it gets between them and the Sun. -- Lunar eclipses - are where the Earth obscures the Sun, from the Moon's point of view. The Moon moves through the shadow cast by the Earth. This can only happen...

Drake Equation
2004-10-19 04:45:41

Drake Equation -- The Drake equation (also known as the Green Bank equation) is a famous result in the speculative fields of xenobiology and the search for extraterrestrial intelligence. This equation was devised by Dr. Frank Drake in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the...

Double Star
2004-10-19 04:45:41

Double Star -- When two stars are so nearly in the same direction as seen from Earth that they appear to be a single star to the naked eye but may be separated by the use of telescopes, they are referred to as a double star. There are two different kinds of double star. In the case where two stars are only apparently close to each other, but which are in fact separated by a great distance...

Quintessence Dark Energy
2004-10-19 04:45:41

Quintessence (Dark Energy) -- Quintessence or dark energy is a hypothetical form of energy postulated to exist in order to explain observations of an accelerating universe. This energy would act like a vacuum pressure, pushing things apart. Other attempts to explain these recent observations involve a non-zero cosmological constant, which has the same effect. Indeed, sometimes...

Crater
2004-10-19 04:45:41

Crater -- A crater is a circular depression on the surface of a planet, moon, asteroid, or other celestial body. Craters are typically caused by meteorite impacts, although some are caused by volcanic activity. In the center of craters on Earth a crater lake often accumulates, and in craters formed by meteorites a central island (caused by rebounding crustal rock after the impact) is...

Word of the Day
lunula
  • A small crescent-shaped structure or marking, especially the white area at the base of a fingernail that resembles a half-moon.
This word is a diminutive of the Latin 'luna,' moon.
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