NASA APOD #38-47

#38 M57: The Ring Nebula July 27, 1995

“July 27, 1995 M57: The Ring Nebula Credit: The Electronic Universe Project, Nelson Caldwell Explanation: A star with mass similar to that of our Sun will throw off its outer gasses after fusion has stopped in its core. Possibly the most visually spectacular of these planetary nebula is the pictured Ring Nebula. The appearance as a ring is really an illusion of projection - the nebula is actually a spherical shell. At the center a blue dot is visible which is the old core of the star, known as a white dwarf. It is still not known exactly how the star throws off the gas that becomes the nebula. For more information on the Ring Nebula see The Electronic Universe Project's write-up. Many images of Messier objects can be found in The Electronic Universe Project's The Galaxy Gallery: Messier Objects."

#39 M82: An Irregular Galaxy July 28, 1995

“July 28, 1995 M82: An Irregular Galaxy Credit: The Electronic Universe Project Explanation: Not all galaxies have spiral structure like our Milky Way. Many have smooth elliptical shapes, but also many have irregular shapes such as the bright sky object M82, the 82nd object on Messier's list. The strange structure of this galaxy is thought to be caused by young stars ejecting gas in energetic bubbles, and by lanes of absorbing dust. For more information on M82 see The Electronic Universe Project's write-up. Many images of Messier objects can be found in The Electronic Universe Project's The Galaxy Gallery: Messier Objects."

#40 M27: The Dumbbell Nebula July 29, 1995

“July 29, 1995 M27: The Dumbbell Nebula Credit: The Electronic Universe Project, Karen Gloria Explanation: The Dumbbell Nebula is a beautiful red and blue planetary nebula in the constellation of Vulpecula. It is the 27th object on Charles Messier's list of diffuse sky objects, and so is referred to as M27. Its high surface brightness makes it a good target for small telescopes. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, astronomers have determined them to be stars surrounded by cocoons of gas blown off in the late stages of evolution. For more information on M27 see The Electronic Universe Project's write-up. Many images of Messier objects can be found in The Electronic Universe Project's The Galaxy Gallery: Messier Objects."

#41 The Rings of Saturn July 30, 1995

“July 30, 1995 The Rings of Saturn Credit: NASA, Jet Propulsion Laboratory, Voyager Project Explanation: Saturn's spectacular system of bright rings has been the subject of study and wonder since Galileo first turned his telescope on the ringed planet in 1610. To Galileo, the blurry image produced by his small telescope was confusing. Saturn appeared to him to have "ear-like" appendages which he thought might be large moons. Eventually, larger telescopes revealed the incredible truth - Saturn was surrounded by bright rings. The image above, made by NASA's Voyager 2 spacecraft, further reveals the intricate structure of the ring system. The image has been computer enhanced and color coded to bring out the subtle details. For more information about the picture see the NASA, JPL press release ."

#42 Exploring Saturn's Rings July 31, 1995

“July 31, 1995 Exploring Saturn's Rings Credit: NASA, Jet Propulsion Laboratory, Voyager Project Explanation: By watching a star flicker and fade as it passed behind Saturn's rings, NASA's Voyager 2 spacecraft was able explore the ring system in amazing detail. Data produced by Voyager's instruments as the star Delta Scorpii was occulted by some of the outer rings was used to reconstruct this image which shows details almost 1000 times smaller than normally possible with Voyager's cameras. For more information about the picture see the NASA, JPL press release ."

#43 Crossing The Ring Plane August 01, 1995

“August 1, 1995 Crossing The Ring Plane Credit: NASA, Hubble Space Telescope Explanation: "I do not know what to say in a case so surprising, so unlooked for and so novel." announced Galileo when Saturn's rings appeared to vanish in 1612. In fact, every 15 years Saturn's rings seem to almost disappear as viewed from the Earth. This happens just as the orbiting Earth crosses the plane of Saturn's rings. The edge on perspective temporarily robs astronomers of a spectacular sight, however, the ring plane crossing affords them the opportunity to measure the rings' thickness and search for undiscovered moons. In this image of Saturn, produced on May 22, 1995 by NASA's Hubble Space Telescope, two of Saturn's known moons are visible as star like objects to the left of the planet. For more information about the ring plane crossing see the Saturn Ring Plane Crossing web page ."

#44 Jupiter's Rings August 02, 1995

“August 2, 1995 Jupiter's Rings Credit: NASA, Voyager Project Explanation: Astronomers using NASA's Voyager spacecraft to search for a ring system around Jupiter discovered these faint rings in 1979. Unlike Saturn's bright rings which are composed of chunks of rock and ice, Jupiter's rings appear to consist of fine particles of dust. One possibility is that the dust is produced by impacts with Jupiter's inner moons. This false color image has been computer enhanced. The gas giant planets, Jupiter, Saturn, Uranus, and Neptune are all known to have rings. For more information about planetary ring systems see the Planetary Rings Node."

#45 Io: A Volcanic Moon August 03, 1995

“August 3, 1995 Io: A Volcanic Moon Credit: NASA, Voyager Project Explanation: In 1610, Galileo turned his telescope to the heavens and discovered that the planet Jupiter had four bright moons. The innermost of these Galilean moons, Io, turned out to be one of the most exotic objects in the solar system. About the size of the earth's moon, Io is covered with volcanoes, many of which are currently active. The material expelled in the volcanic eruptions may contain compounds of Sulfur which take on a variety of colors and could account for its mottled, "pizza-like" appearance. For a report of a recent eruption of an Io volcano, see the NASA Infrared Telescope Facility press release and photo ."

#46 Closeup of an Io Volcano August 04, 1995

“August 4, 1995 Closeup of an Io Volcano Credit: NASA, Voyager Project, Copyright Calvin J. Hamilton Explanation: In 1979, one of NASA's Voyager spacecraft made a spectacular and unexpected discovery. Io, the innermost Galilean moon of Jupiter, was covered with volcanoes and some of them were erupting! In all, Voyager 1 observed nine volcanic eruptions during its encounter with the moon. When Voyager 2 flew past four months later it was able to confirm that at least six of them were still erupting. This Voyager image of Ra Patera, a large shield volcano, shows colorful flows up to about 200 miles long emanating from the dark central volcanic vent. For more information about volcanism on Io, see Calvin J. Hamilton's Io page"

#47 Geysers on Triton August 05, 1995

“August 5, 1995 Geysers on Triton Credit: NASA, Voyager Project, Copyright Calvin J. Hamilton Explanation: In August of 1989 NASA's Voyager 2 spacecraft passed by Neptune, the most distant of the solar system's gas giant planets. Its encounter with Neptune climaxed with its closest approach to Neptune's largest moon Triton. From a distance of about 24,000 miles the robot space probe surveyed Triton's surface, whose temperature averages nearly -400 degrees Fahrenheit, and discovered surprising evidence of a complex and active world. For example, the prominent dark streaks in this image seem to come from small volcanoes and may consist of nitrogen frost mixed with organic compounds ejected during geyser-like eruptions. For more information about Triton, see Calvin J. Hamilton's Triton page ."

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