Nestled within the dusty arms of the large spiral galaxy Andromeda (M31), the star cluster NGC 206 is one of the largest star forming regions known in our local group of galaxies. The beautiful bright blue stars of NGC 206 betray its youth - but close, systematic studies of variable stars in and around NGC 206 will also accurately reveal its distance. Astronomers are searching for variable stars in NGC 206, particularly pulsating stars known as Cepheids and eclipsing binary star systems. Distances for these types of stars can be effectively determined by following the periodic changes in their brightness and spectra. About 3 million light-years away, an accurately known distance to NGC 206 and thus M31 is critical to the larger understanding of galaxy formation, galaxy evolution, and ultimately the distance scale of the Universe.
Comet Shoemaker-Levy 9, named after its co-discoverers, was often referred to as the "string of pearls" comet. It is famous for its suggestive appearance as well as its collision with the planet Jupiter! The comet's original single nucleus was torn to pieces by Jupiter's strong gravity during a close encounter with the solar system's largest planet in 1992. The pieces are seen (scroll right) in this composite of Hubble Space Telescope images to be "pearls" strung out along the comet's orbital path. In July of 1994 these pieces collided with Jupiter in a rare and spectacular series of events.
Sputnik means "traveling companion". Despite the innocuous sounding name, the launch of the Earth's first "artificial moon", Sputnik 1, by the Soviet Union on October 4, 1957 shocked the free world, setting in motion events which resulted in the creation of NASA and the race to the Moon. Sputnik 1 was a 184 pound, 22 inch diameter sphere with four whip antennas connected to battery powered transmitters. The transmitters broadcast a continuous "beeping" signal to an astounded earthbound audience for 23 days. A short month later, on November 3, the Soviet Union followed this success by launching a dog into orbit aboard Sputnik 2.
As expected, the ozone hole near Earth's South Pole is back again this year. This time, however, it's smaller than the past two years, and has an unusual double lobe structure. Ozone is important because it shields us from damaging ultraviolet sunlight. Ozone is vulnerable, though, to CFCs and halons being released into the atmosphere. International efforts to reduce the use of these damaging chemicals appear to be having a positive effect on their atmospheric abundance. The smaller size of the ozone hole this year, however, is attributed mostly to warmer than normal air in the surrounding stratosphere. The above picture of the ozone hole was taken on September 24 by TOMS on board the orbiting Earth Probe satellite.
The 2003 Leonids Meteor Shower contained relatively few meteors. As expected and unlike the last few years, the Earth just did not pass through any dense particle streams left over by the Sun-orbiting Comet Tempel-Tuttle. Preliminary reports had the peak meteor rates only as high as about one relatively faint meteor a minute even from good locations at good times. Pictured above is one of the brighter Leonids of 2003, caught by one of the continuously operating night sky web cameras (CONCAMs) of the global Night Sky Live project. The fisheye image shows the night sky from horizon to horizon above Mauna Kea, Hawaii, USA. The image is annotated with several bright stars and planets. Note that this meteor, as do all Leonids, appears to emanate from the constellation Leo, labeled on the upper left. Although the peak of the Leonids this year was on November 19, this meteor flashed through the sky the next night.
Where is the center of the unusual Egg Nebula? Like a baby chick pecking its way out of an egg, the star in the center of the Egg Nebula is casting away shells of gas and dust as it slowly transforms itself into a white dwarf star. The Egg Nebula is a rapidly evolving pre-planetary nebula spanning about one light year toward the constellation of Cygnus. Thick dust, though, blocks the center star from view, while the dust shells further out reflect light from this star. Light vibrating in the plane defined by each dust grain, the central star, and the observer is preferentially reflected, causing an effect known as polarization. Measuring the orientation of the polarized light for the Egg Nebula gives clues to location of the hidden source. The above image taken by the Advanced Camera for Surveys on the Hubble Space Telescope is false-color coded to highlight the orientation of polarization. Have you seen this week's: HEASARC Picture of the Week?
Big, beautiful, barred spiral galaxy NGC 1300 lies some 70 million light-years away on the banks of the constellation Eridanus. This Hubble Space Telescope composite view of the gorgeous island universe is one of the largest Hubble images ever made of a complete galaxy. NGC 1300 spans over 100,000 light-years and the Hubble image reveals striking details of the galaxy's dominant central bar and majestic spiral arms. In fact, on close inspection the nucleus of this classic barred spiral itself shows a remarkable region of spiral structure about 3,000 light-years across. Like other spiral galaxies, including our own Milky Way, NGC 1300 is thought to have a supermassive central black hole.
The first to orbit Mercury, the MESSENGER spacecraft came to rest on this region of Mercury's surface yesterday. Constructed from MESSENGER image and laser altimeter data, the scene looks north over the northeastern rim of the broad, lava filled Shakespeare basin. The large, 48 kilometer (30 mile) wide crater Janacek is near the upper left edge. Terrain height is color coded with red regions about 3 kilometers above blue ones. MESSENGER'S final orbit was predicted to end near the center, with the spacecraft impacting the surface at nearly 4 kilometers per second (over 8,700 miles per hour) and creating a new crater about 16 meters (52 feet) in diameter. The impact on the far side of Mercury was not observed by telescopes, but confirmed when no signal was detected from the spacecraft given time to emerge from behind the planet. Launched in 2004, the MErcury Surface, Space ENvironment, GEochemisty and Ranging spacecraft completed over 4,000 orbits after reaching the Solar System's innermost planet in 2011.
Watching and waiting, astronomers have uncovered the presence of more than 70 planets orbiting stars other than the Sun. So far almost all these extrasolar planets have crazy elongated orbits, lie uncomfortably close to their parent stars, or are found in bizarre, inhospitable systems. Yet a reported new planet discovery indicates for the first time that a nearby sun-like star, 47 Ursae Majoris (47 UMa), has at least two planets in nearly circular orbits more reminiscent of Jupiter and Saturn in our own familiar Solar System. The planets are too distant and faint to be photographed directly. Still, 13 years of spectroscopic observations of 47 UMa have revealed the wobbling signature of a second planet intertwined with one previously known. In this artist's illustration, the worlds of 47 UMa hang over the rugged volcanic landscape of a hypothetical moon. The moon orbits the newly discovered planet, imagined here with Saturn-like rings, while the previously known planet is visible as a tiny crescent, close to the yellowish star. Closer still to 47 UMa is another tiny dot, a hypothetical Earth-like water world. About 51 light-years distant, 47 UMa can be found in planet Earth's sky near the Big Dipper.
Spectacular details of rover tracks, wind-driven soil, and textured rocks on the Martian surface fill this color mosaic. The view is north-northeast from the Sagan Memorial Station at the Pathfinder landing site on Mars. These images are just part of the "Super Panorama" - a detailed color and stereo imaging data set being compiled by Pathfinder's IMP camera. The data set will be used to derive detailed topographic maps of the landing site and to further explore the mineralogy of the martian rocks and soil. The forward rover deployment ramp and the rock named Barnacle Bill, appear in the foreground at the left while the larger Yogi rock is partly visible at the upper right. Criss-crossing tracks were made by the cruising Sojourner robot rover's spiked wheels. With three wheels on each side, the two foot long rover makes tracks about 1.5 feet apart.