Astronomy Picture of the Day
APOD: 2005 February 7 - A Telescope Laser Creates an Artificial Star
Explanation: What do you get when you combine one of the world's most powerful telescopes with a powerful laser? An artificial star. Monitoring fluctuations in brightness of a genuine bright star can indicate how the Earth's atmosphere is changing, but many times no bright star exists in the direction where atmospheric information is needed. Therefore, astronomers have developed the ability to create an artificial star where they need it -- with a laser. Subsequent observations of the artificial laser guide star can reveal information so detailed about the blurring effects of the Earth's atmosphere that much of this blurring can be removed by rapidly flexing the mirror. Such adaptive optic techniques allow high-resolution ground-based observations of real stars, planets, nebulae, and the early universe. Above, a laser beam shoots out of the Keck II 10-metre telescope on Mauna Kea in Hawaii in 2002, creating an artificial star.
APOD: 2006 May 14 - The Very Large Array of Radio Telescopes
Explanation: The most photogenic array of radio telescopes in the world has also been one of the most productive. Each of the 27 radio telescopes in the Very Large Array (VLA) is the size of a house and can be moved on train tracks. The above pictured VLA, inaugurated in 1980 is situated in New Mexico, USA. The VLA has been used to discover water on planet Mercury, radio-bright coronae around ordinary stars, micro-quasars in our Galaxy, gravitationally-induced Einstein rings around distant galaxies, and radio counterparts to cosmologically distant gamma-ray bursts. The vast size of the VLA has allowed astronomers to study the details of super-fast cosmic jets, and even map the centre of our Galaxy. An upgrade of the VLA is being planned.
APOD: 1999 February 1 - The Subaru Telescope
Explanation: Last week, Japan's new Subaru Telescope made its first observations of the sky. The gray building housing Subaru is visible just left of the white Keck domes near the photo's centre. Subaru is the latest in the class of optical telescopes using a mirror with a diameter greater than 8 metres. Subaru's 8.3-metre primary is the largest single-piece optical telescope mirror yet made, and is so thin that its precise shape can be monitored and adjusted. Subaru will be owned and operated by Japan but located at the top of Hawaii's Mauna Kea, a dormant volcano famous for housing several of the world's leading telescopes.
APOD: 2003 September 9 - A Gemini Sky
Explanation: Where will Gemini take us tonight? It is dusk and Gemini North, one of the largest telescopes on planet Earth, prepares to peer into the distant universe. Gemini's flexible 8.1-mirror has taken already effectively taken humanity to distant stars, nebulae, galaxies, and quasars, telling us about the geometry, composition, and evolution of our universe. The above picture is actually a composite of over 40 images taken while the Gemini dome rotated, later adding an image of the star field taken from the same location. The Gemini dome is not transparent -- it only appears so because it rotated during the exposures of this image. The constellations of Scorpius and Sagittarius can be seen above the dome, as well as the sweeping band of our Milky Way Galaxy, including the direction toward the Galactic centre. Gemini North's twin, Gemini South, resides in Cerro Pachn, Chile. This night, 2003 August 19, Gemini North took us only into the outer Solar System, observing Pluto in an effort to better determine the composition of its thin atmosphere.
APOD: 2002 August 19 - Roque de los Muchachos Observatory
Explanation: Above the clouds, atop an island off the coast of Africa, a group of cutting-edge telescopes inspects the universe. Pictured above are telescopes at Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, Spain. The site is one of the premier observing locations on Earth. The telescopes pictured are, from left to right, the Carlsberg Meridian Telescope, the 4.2-metre William Herschel Telescope, the Dutch Open Telescope, the Swedish Solar Tower, the 2.5-metre Isaac Newton Telescope, and the 1.0-metre Jacobus Kapteyn Telescope. Pioneering observations made recently by these telescopes include stars and galaxies forming early in our universe, comets breaking up, and evidence for planets around Sun-like stars.
APOD: 2000 October 30 - A Step Toward Gravitational Wave Detection
Explanation: Accelerate a charge and you'll get electromagnetic radiation: light. But accelerate any mass and you'll get gravitational radiation. Light is seen all the time, but, so far, a confirmed direct detection of gravitational radiation has yet to be made. When absorbed, gravitational waves (GWs) create a tiny symmetric jiggle similar to squashing a rubber ball and letting go quickly. Separated detectors can be used to discern GWs from everyday bumps. Powerful astronomical GW sources would coincidentally jiggle even detectors on opposite ends of the Earth. Pictured above are the two-kilometre-long arms of one such detector: the LIGO Hanford Observatory in Washington, which recently achieved a phase-lock milestone to future GW detection. When it and its sister interferometer in Louisiana come online in 2002, they may see a GW sky so strange it won't be immediately understood. APOD mourns the recent passing of Joseph Weber, a visionary thinker and pioneer in gravitational wave detection.
APOD: 2000 August 17 - Mount Megantic Magnetic Storm
Explanation: Plasma from the Sun and debris from a comet both collided with planet Earth last Saturday morning triggering magnetic storms and a meteor shower in a dazzling atmospheric spectacle. The debris stream from comet Swift-Tuttle is anticipated yearly, and many skygazers already planned to watch the peak of the annual Perseids meteor shower in the dark hours of August 11/12. But the simultaneous, widely reported aurorae were triggered by the chance arrival of something much less predictable -- a solar coronal mass ejection. This massive bubble of energetic plasma was seen leaving the active Sun's surface on August 9, just in time to travel to Earth and disrupt the planet's magnetic field triggering extensive aurorae during the meteor shower's peak! Inspired by the cosmic light show, Sebastien Gauthier photographed the colourful auroral displays above the dramatic dome of the Mount-Megantic Popular Observatory in southern Quebec, Canada. Bright Jupiter and giant star Aldebaran can be seen peering through the shimmering northern lights at the upper right.
APOD: 2000 July 15 - Star Trails in Southern Skies
Explanation: As the Earth spins on its axis, the stars seem to rotate around us. This motion produces the beautiful concentric arcs traced out by the stars in this time exposure of the southern hemisphere night sky. In the foreground is the dome of the Anglo-Australian Telescope in central New South Wales, Australia. In the middle of the picture is the South Celestial Pole, the projection of Earth's axis of rotation into the southern sky. While the bright star Polaris lies conveniently close to the North Celestial Pole, no bright star similarly marks the pole in the south. Still, the South Celestial Pole is easily identified in the picture as the point in the sky at the centre of all the star trail arcs.
APOD: 2000 April 10 - Aurora in Red and Yellow
Explanation: The past week brought some spectacular aurora to northern skies. These aurorae were caused by a large interplanetary shock wave that exploded from the Sun on April 4. When the shock wave reached the Earth on April 6, the resulting aurora could be seen in clear skies as far south as North Carolina. As the aurorae occurred high in the Earth's atmosphere, they were accompanied by an unusual alignment of planets far in the background. Pictured above that night, an unusual multicoloured auroral display graced the skies above the domes of the Brno Observatory in the Czech Republic.
APOD: 1998 November 24 - Seven Leonids Over Wise Observatory
Explanation: More Leonids were visible at some places than others. In Israel, early in the morning of 17 November, it rained meteors though a clear sky. Observers there reported a peak rate for the 1998 Leonid Meteor Shower of about 600 meteors per hour. Visible in the above picture are no fewer than seven Leonid meteors occurring over just a few minutes. (Can you find them all?) The dome of the Wise Observatory is visible on the right. The Earth's rotation causes stars to appear as arcs. The 1998 Leonids might be remembered not for their numbers, however, but for the unusually high fraction of bright fireballs. Another eventful Leonid Meteor Shower is forecast for the same time next year.
APOD: 1997 December 27 - Keck: The Largest Optical Telescopes
Explanation: In buildings eight stories tall rest mirrors ten metres across that are slowly allowing humanity to map the universe. Alone, each is the world's largest optical telescope: Keck. Together, the twin Keck telescopes have the resolving power of a single telescope 90-metre in diameter, able to discern sources just milliarcseconds apart. Since opening in 1992, the real power of Keck I (left) has been in its enormous light-gathering ability - allowing astronomers to study faint and distant objects in our Galaxy and the universe. Keck II, completed last year, and its twin are located on the dormant volcano Mauna Kea, Hawaii, USA. In the distance is Maui's volcano Haleakala. One reason Keck was built was because of the difficulty for astronomers to get funding for a smaller telescope.
APOD: 2000 July 7 - Sirius, Sun, Moon, and Southern Cross
Explanation: >From left to right are the enclosures of Yepun (ye-poon; Sirius), Antu (an-too; Sun), Kueyen (qua-yen; Moon), and Melipal (me-li-pal; Southern Cross), pictured here as night falls at Paranal Observatory in northern Chile. These are the four 8.2 metre wide telescope units of the European Southern Observatory's Very Large Telescope (VLT). ESO astronomers and engineers plan to combine the light of the individual units, achieving an equivalent aperture of 16.4 metres which will, for a while, constitue the biggest telescope on planet Earth. Of course, the individual telescopes also function independently. Antu, Kueyen, and Melipal have already achieved first light with Yepun expected to operate in 2001. The telescope names come from the Mapuche language. They were unanimously chosen based on the winning "name-the-telescopes" essay by 17-year old Jorssy Albanez Castilla from Chuquicamata near the city of Calama.
APOD: 2001 July 10 - Sudbury Indicates Nonstandard Particle Model
Explanation: The Sudbury Neutrino Observatory (SNO) has been detecting so few neutrinos from the Sun that the Standard Model of fundamental particles in the universe may have to be revised. Pictured above is the SNO as it was being built. Now operating, this large sphere beneath Canada is detecting nearly invisible particles called neutrinos being emitted from the centre of the Sun. SNO appears to be measuring a rate expected for all types of neutrinos combined but a decided deficit for the electron neutrino. The results are being interpreted as bolstering previous evidence that different types of neutrinos are changing into each other. The most popular model for fundamental particles, known as the Standard Model, did not predict such schizophrenic neutrinos. Implications include that neutrinos have mass and therefore comprise some of the dark matter in the universe, although probably not a cosmologically significant amount.
APOD: 2003 June 23 - KamLAND Verifies the Sun
Explanation: A large sphere beneath Japan has helped verify humanity's understanding of the inner workings of the Sun. The KamLAND sphere, shown above during construction in 2001, fails to detect fundamental particles called anti-neutrinos that are known to be emitted by nearby nuclear reactors around Japan. This triumphant failure can best be explained by neutrinos oscillating between different types. KamLAND's results bolster previous neutrino oscillation claims including that from the Sudbury detector, a similar large sphere beneath Canada designed to detect all types of neutrinos from the Sun. Thus, leading astrophysicists now consider the long standing solar neutrino deficit problem as finally solved. A new mystery that replaces it is to find a new Standard Model for particle physics that fully explains neutrino oscillations.
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