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A Solar Flare
Big Bear Solar Observatory
This movie shows material erupting from a flare near the limb of the Sun on October 10, 1971. The ejected material is heated to many millions of degrees and produces an energy equivalent to as much as a million megatons of TNT. Flares are short bursts (5-10 minutes) of energy from the Sun. The origin of flares is not well understood, but it is thought that they are related to the liberation of energy stored in the solar corona.
Video: 4 MB, Quicktime MOV
Flare Monitoring
Flares are categorized by their brightness in X-Rays. The most energetic flares are X-Class flares followed by M-Class and C-Class. X-Class flares have a tenth the energy of M flares and C-Class flares have a tenth of the energy of an M flare. The National Oceanic and Atmospheric Administration monitors the X-Ray energy from the Sun using satellites. The radiation from flares disrupts the Earth's ionosphere, causing communication blackouts and power outages, and the Northern and Southern lights.
Ellen Cohen
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Phases of the Moon
António Cidadão
Video: 739 kB, MPEG
This is an animation that shows the Moon through one lunar cycle, revealing all of its phases from New Moon to New Moon. The phases of the Moon are caused by the relative positions of the Sun, Earth, and Moon. The Moon orbits the Earth, on average, every 27 days (27 days, 7 hours, 43 minutes, to be precise). Because it simply reflects sunlight, the amount of illuminated surface we see depends on where the Moon is in its orbit.
Motions of the Moon
The phases of the Moon change depending on where the Moon is in its orbit around the Earth. If the Moon is in the direction of the Sun, then we call it a New Moon. In this case, the entire back side of the Moon is illuminated, leaving the side we see in darkness. About seven days later, the Moon is in First Quarter phase; the illuminated portion we see is a quarter of the entire Moon (the other illuminated quarter is on the back side of the Moon). In another seven days the Moon will be opposite the Sun, rising when the Sun sets and setting when the Sun rises. This is a Full Moon, when the entire disk as seen from Earth is illuminated. After Full Moon, the Moon is waning, the illuminated portion grows smaller and smaller. Seven days after Full is Third Quarter, and then finally another New Moon, when the Moon rises approximately when the Sun rises, is in the sky all day, and sets when the Sun sets.
Ellen Cohen
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The Surface of Pluto
Alan Stern (Southwest Research Institute), Marc Buie (Lowell Observatory), NASA and ESA
Since its discovery in 1930, Pluto has remained one of the more mysterious bodies in the Solar System. In 1996, the Hubble Space Telescope observed Pluto, taking snapshots as it rotated through its 6.4-day period. The results, quite surprisingly, showed that the surface of Pluto is complex with more large-scale contrast than any planet except Earth. The images show about a dozen distinctive albedo features, or regions, that had not been seen before. Among these include a ragged
northern polar cap bisected by a dark strip, a bright linear marking, and other dark and bright spots on the surface. The images also confirm the presence of polar caps, which had been inferred since the 1980s.
Video: 614 kB, MPEG
Pluto's Distance and surface composition
Because Pluto is so far from the Sun (5.8 billion kilometers or 3.7 billion miles), its surface is composed of a complex distribution of frosts. These frosts migrate seasonally across the surface, just as they do on Earth. However, the seasons on Pluto are not caused by its tilt as on Earth, but result from the distance of Pluto from the Sun. Pluto's average distance is 39.44 AU, but it ranges from 29.7 to 49.3 AU (1 AU is defined to be the average distance between the Earth and the Sun and equals 149 million kilometers or 93 million miles). Because of this variation in distance, when Pluto is further from the Sun nitrogen, carbon monoxide, and methane gases partially freeze on the surface. During the warm
season, when Pluto is closer to the Sun, these ices sublimate (go directly from solid to gas) enhancing Pluto's atmosphere.
Ellen Cohen
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