Browse Reference Articles
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Supergiant
Supergiants are the most massive stars. Supergiants can have masses from 10 to 70 solar masses and brightness from 30,000 up to hundreds of thousands times the solar luminosity. They vary greatly in ... > more -
Impact crater
An impact crater is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial body, caused by a collision of a smaller body (meteor) with the ... > more -
Light-year
A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in a vacuum in one year. While there is no authoritative decision on which year is ... > more -
Aurora (astronomy)
The aurora is a glow observed in the night sky, usually in the polar zone. It is also known as "northern lights" or "aurora borealis," which is Latin for "northern dawn" since in Europe especially, ... > more -
Comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9 (SL9, formally designated D/1993 F2) was a comet which collided with Jupiter in 1994, providing the first direct observation of the collision of two solar system ... > more -
Exploration of Mars
The exploration of Mars has been an important part of the space exploration missions of the Soviet Union (later Russia), the United States, Europe, and Japan. Dozens of unmanned spacecraft, including ... > more -
Geosynchronous orbit
A geosynchronous orbit is a geocentric orbit that has the same orbital period as the sidereal rotation period of the Earth. It has a semi-major axis of 42,164 km (26,200 miles). In the special case ... > more -
Stellar evolution
In astronomy, stellar evolution is the sequence of changes that a star undergoes during its lifetime; the hundreds of thousands, millions or billions of years during which it emits light and heat. ... > more -
Cepheid variable
A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. Since the ... > more
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