Astronomy fanatica

last SG · 2005-02-27T00:18:37+00:00

u'll find it on page 4 of this thread

poon cho tang SG

Astronomy Picture of the Day

2005 July 13

Analemma of the Moon

Explanation: An analemma is that figure-8 curve you get when you mark the position of the Sun at the same time each day for one year. But the trick to imaging an analemma of the Moon is to understand that on average the Moon returns to the same position in the sky about 51 minutes later each day. So, if you photograph the Moon 51 minutes later on successive days, over one lunation or lunar month it will trace out an analemma-like curve as the actual position of the Moon wanders compared to the average -- due to the Moon's tilted and elliptical orbit. For this excellent demonstration of the lunar analemma, astronomer Rich Richins chose the lunar month containing this year's northern hemisphere summer solstice. The southernmost Full Moon rises at the lower right above the Organ Mountains in southern New Mexico, USA, with the New Moon phase at the upper left. The multiple exposure image required some digital manipulation, particularly to include thin crescent phases in daytime skies.

Credit & Copyright: Rich Richins

poon cho tang SG

Keck telescopes

The W.M. Keck telescopes are the two largest optical/near-infrared telescopes of the Mauna Kea Observatory on Mauna Kea in Hawai'i. These are reflecting telescopes located at an altitude of 4,145 m (13,600 ft). Keck I started observing in 1993 and Keck II started in 1996. This is a Ritchey-Chrétien type of telescope on an altazimuth mount, assisted by active optics. The Keck telescopes have, essentially, 10 m mirrors; however, rather than having one mirror each telescope has 36 smaller hexagonal mirrors working together. In addition, Keck I and II can work together, via interferometry; this gives them the effective power of an 85 m mirror.

The Mauna Kea Observatory, an institute of the University of Hawai'i, is considered one of the most important land-based observatories in the world for its isolated, unobstructed views of space without interference from man-made light sources. The twin Keck telescopes are the largest of its optical/near-infrared instruments.

The telescopes are administered by the University of California, California Institute of Technology and the National Aeronautics and Space Administration. They sit on land leased from the University of Hawai'i System based in Honolulu, Hawai'i.

Issue #139

poon cho tang SG

Astronomy Picture of the Day

2005 July 14

Star Trails Over Vienna

Explanation: As the Earth spins on its axis, the sky seems to rotate around us. This motion, called diurnal motion, produces the beautiful concentric trails traced by stars during time exposures. In the middle of the picture is the North Celestial Pole (NCP), easily identified as the point in the sky at the center of all the star trail arcs. The star Polaris, commonly known as the North Star, made the very short bright circle near the NCP. Full circle star trails are pictured over Vienna, Austria. This image, a relatively short exposure followed by a digital trick, could not have been taken during a single night because 24-hours are needed for one full rotation, and the Sun is sure to dominate the frame at some time.

Credit & Copyright: Peter Wienerroither (U. Wien)

Large Binocular Telescope

The Large Binocular Telescope (originally named the Columbus Project) is a joint project of the Italian astronomical community (represented by the Istituto Nazionale di Astrofisica (INAF)), the University of Arizona, Arizona State University, Northern Arizona University, the LBT Beteiligungsgesellschaft in Germany Max-Planck-Institut für Astronomie in Heidelberg, Landessternwarte in Heidelberg, Astrophysikalisches Institut in Potsdam, Max-Planck-Institut für Extraterrestrische Physik in Munich, and Max-Planck-Institut für Radioastronomie in Bonn), The Ohio State University, Research Corporation in Tucson, and the University of Notre Dame.

The Large Binocular Telescope

The final configuration will be a telescope with two 8.4-meter mirrors mounted on a common base (hence the name "binocular"), taking full advantage of the active and adaptive optics provided by Arcetri Observatory. Also, an interferometric mode will be available, with a baseline of 23 meters.

When the LBT is fully operational, it will be the world's most technologically advanced optical telescope, creating images in the near-infrared expected to be nearly 10 times sharper than images from the Hubble Space Telescope.

LBT on the cover of VMEbus Systems magazine

It is located on the 10,700-foot Mount Graham in southeastern Arizona. The choice of location sparked considerable local controversy, both among the San Carlos Apache Tribe who claimed the mountain as sacred and environmentalists who contended that the observatory would cause the demise of the endangered Mount Graham red squirrel. Environmentalists and members of the tribe filed some 40 lawsuits - eight of which ended up before a federal appeals court - but the project ultimately prevailed after an act of Congress.

The telescope and mountain observatory also survived two major forest fires in eight years, the most recent in the summer of 2004.

Forest fire approaches the LBT in July 2004.

The telescope was dedicated in October 2004 and is expected to be complete in 2005.

Issue #140

Astronomy Picture of the Day

2005 July 15

Reflections on the Inner Solar System

Explanation: Only Mars is missing from this reflective view of the major rocky bodies of the inner solar system. Captured on July 8th, the serene, twilight picture looks out over the Flat Tops Wilderness area from near Toponas, Colorado, USA and includes planets Mercury, Venus, Earth, and Earth's large natural satellite, the Moon. The Moon is in a young crescent phase about three degrees above bright planet Venus. Forest fires contribute to a layer of smoke in Earth's sky that almost hides planet Mercury, still visible very near the horizon. Just a week earlier Venus and Mercury were joined by Saturn, forming a notable grouping in the west also enjoyed by skygazers across planet Earth.

Credit & Copyright: Jimmy Westlake (Colorado Mountain College)

Subaru Telescope

Subaru Telescope is the 8.3 meter flagship telescope of the National Astronomical Observatory of Japan. It is named for the open star cluster known in English as the Pleiades. It is located on top of Mauna Kea in Hawaii.

The Subaru Telescope at sunset

Issue #141

Astronomy Picture of the Day

2005 July 16

Galaxy Group HCG 87

Explanation: Posing for this cosmic family photo are the galaxies of HCG (Hickson Compact Group) 87, about four hundred million light-years distant toward the amphibious constellation Capricornus. The large edge-on spiral near picture center, the fuzzy elliptical galaxy immediately to its right, and the spiral near the top of the image are identified members of the group, while the small spiral galaxy in the middle is likely a more distant background galaxy. In any event, a careful examination of the deep image reveals other galaxies which certainly lie far beyond HCG 87. While not exactly locked in a group hug, the HCG 87 galaxies are interacting gravitationally, influencing their fellow group members' structure and evolution. This image is from the commissioning phase of an instrument on the Gemini Observatory's South Telescope at Cerro Pachon, Chile. It compares favorably with views of this photogenic galaxy group recorded by the Hubble Space Telescope.

Credit: GMOS-S Commissioning Team, Gemini Observatory

Very Large Telescope

The Very Large Telescope Project (VLT) consists of a system of four separate optical telescopes (the Antu telescope, the Kueyen telescope, the Melipal telescope, and the Yepun telescope) organized in an array formation. Each telescope has an 8.2 m aperture. The project is organized by the European Southern Observatory.

VLT is located at the Paranal Observatory on Cerro Paranal, a 2,635 m high mountain in the Atacama desert in northern Chile.

The four telescopes of the European Southern Observatory Paranal site. The VLTI (Very Large Telescope Interferometer) building is the low structure in front of the telescopes. Image courtesy of the European Southern Observatory.

General Information
Organization: European Southern Observatory
Location: Cerro Paranal, Atacama desert, Chile
Coordinates: 24° 37' 38" S 70° 24' 17" W
Altitude: 2,635 m
Weather: >340 clear nights/year
Webpage: Paranal observatory

Telescopes
Antu: 8,2 m reflector
Kueyen: 8,2 m reflector
Melipal: 8,2 m reflector
Yepun: 8,2 m reflector

General information

The VLT consists of a cluster of four large (8 meter diameter) telescopes, and an interferometer (VLTI) which will be used to resolve fine features. The interferometer will include a set of 1.8 meter diameter telescopes dedicated to interferometric observations. The 8 meter telescopes have been named after the names of some astronomical objects in the local Mapuche language: Antu (The Sun), Kueyen (The Moon), Melipal (The Southern Cross), and Yepun (Venus).

One of the four telescopes that make up the VLT, named Kueyen. The 8.2 m mirror can be seen below the large horizontal grey beam (as an oval patch of lightness). Image courtesy of the European Southern Observatory.

The VLT 8 meter telescopes can be operated in three modes:

- as a set of independent telescopes (this is the primary mode of operation)
- as a single large incoherent instrument, for extra light-gathering capacity (this mode has now been abandoned)
- as a single large coherent interferometric instrument (the VLT Interferometer or VLTI), for extra resolution (this is occasionally used, usually for observations of relatively bright sources)

The principle role of the VLT is to operate as four independent telescopes, and the interferometry (combining light from multiple telescopes) is a minor secondary role.

The VLT is operated by the European Southern Observatory.

In 2005, VLT telescopes produced some of the first infrared images of extrasolar planets GQ Lupi b and 2M1207b.

Interferometry and the VLTI

Most interferometry will be done using 1.8 meter Auxiliary Telescopes (ATs), which will be dedicated to full-time interferometric measurements. The first observations using a pair of ATs were conducted in February 2005, and additional ATs are expected to be installed soon. For many interferometric observations there is little benefit in using 8 meter telescopes rather than 1.8 meter telescopes.

In its full interferometric operating mode, the four telescopes provide the same light gathering ability (neglecting light losses from the throughput of the instrument) as a single 16 m telescope, making it theoretically the largest optical telescope in the world (the interferometric technique used at the VLTI is not suitable for observing very faint sources, so it actually has poorer sensitivity than the single 8m telescopes). The light from the telescopes is reflected off mirrors and directed through tunnels to a central beam combining laboratory. The VLT is intended to achieve an effective angular resolution of 0.001 arcsecond at a wavelength of 1 µm, comparable to that achieved using other arrays such as the Navy Prototype Optical Interferometer and the CHARA Array.

The poor brightness sensitivity of interferometric observations mean that they could not be used for imaging objects with low surface brightness such as the moon. Only targets which are at temperatures of more than 1000 °C have a surface brightness high enough to be observed in the mid-infrared, and objects must be at several thousands of degrees for near-infrared observations using the VLTI. This sensitivity limit rules out interferometric observations of most solar-system objects apart from the Sun. All the stars visible to the naked eye have temperatures of several thousand degrees, and have large enough surface brightnesses and angular sizes to be observed by the VLTI. Although the use of large telescope diameters and adaptive optics correction can improve the sensitivity a small amount, this cannot extend the reach of optical interferometry beyond nearby stars and the brightest active galactic nucleii.

The first two instruments at the VLTI were VINCI and MIDI, which only allowed two telescopes to be used at any one time. With the installation of the three-telescope AMBER closure-phase instrument in 2005, the first imaging observations from the VLTI are expected soon. In 2008 the PRIMA instrument will further enhance the imaging capabilities of the VLTI by allowing phase-referenced imaging.

After falling drastically behind schedule and failing to meet some specifications, in December 2004 the VLT Interferometer became the target of a second ESO recovery plan. This involves additional effort concentrated on more rapid improvements to fringe tracking and the performance of the main delay lines. Note that this only applies to the interferometer and not other instruments on Paranal.

Issue #142

Astronomy Picture of the Day

2005 July 17

The Center of Centaurus A

Explanation: A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A. This mosaic of Hubble Space Telescope images taken in blue, green, and red light has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun! Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy.

Credit: E.J. Schreier (STScI) et al., HST, NASA

William Herschel Telescope

The William Herschel Telescope or WHT was first conceived in the late 1960s, when the Anglo-Australian Observatory was being designed. The British astronomical community saw the need for telescopes of comparable power in the Northern Hemisphere. Planning began in 1974, but by 1979 the project was on the verge of being scrapped due to a ballooning budget. A re-design cut the price-tage substantially, and Dutch astronomers took a 20% stake in the project, allowing the project to be given the go-ahead in 1981. That year was the 200th anniverary of the discovery of Uranus by William Herschel, and it was decided to name the telescope in his honour. The telescope is a member of the Isaac Newton Group of Telescopes.

Moonrise over the William Herschel Telescope, La Palma, Spain.
The telescopes are (from left to right):
1. The Swedish Solar Telescope
2. The Dutch Open Telescope
3. The Nordic Optical Telescope
4. The William Herschel Telescope

General Information
Organization: Isaac Newton Group of Telescopes
Location: Roque de los Muchachos Observatory, La Palma, Canary Islands
Wavelength regime: Optical
Completion date: June 1st, 1987
Webpage: WHT Homepage

Physical characteristics
Telescope style: Cassegrain-Nasmyth Reflector
Diameter: 4.2 m
Collecting area: 13.8 m²
Mounting: Alt-azimuth

Construction began in 1983, and the telescope was shipped to La Palma in 1985. It saw first light in 1987. The telescope has an altazimuth mount. The mirror is maintained so that its theoretical maximum resolution is less than 0.2 arcseconds. The typical seeing at La Palma is of the order of one arcsecond, so the telescope is limited by that.

As one of the best telescopes in the world, the WHT is heavily over-subscribed, and typically three times more applications for telescope time are received than can be accommodated. Notable discoveries made using the WHT include that of a hot bubble of expanding gas at the centre of the galaxy, suggestive of the presence of a supermassive black hole; the first observation of the optical counterpart of a gamma-ray burst; and recently, the discovery of a Wolf-Rayet star with the fastest-known stellar wind.

Issue #143

Astronomy Picture of the Day

2005 July 18

Deep Impact on Comet Tempel 1 from Hubble

Explanation: It was a human-made event visible across the Solar System. At the direction of terrestrial scientists, a refrigerator-sized probe from the Deep Impact mission struck Comet Tempel 1 on July 4 at over 35,000 kilometers per hour. The unexpectedly bright explosion was not nuclear but rather originated from a large plume that reflected back sunlight. Pictured above is how the event looked to the Earth-orbiting Hubble Space Telescope. A large cloud of bright material is seen emanating from the comet's nucleus and then dispersing. The area encompassing the comet became over three times brighter in the hours after the impact. Astronomers will continue to study the images and data returned by Deep Impact to better determine the nature of Comet Tempel 1 and discern clues about the formation dynamics of the early Solar System.

Credit: P. Feldman (JHU) & H. Weaver (APL), ESA, NASA

Paris 1900 Exposition Refractor

The largest refractor ever constructed was French. It was on display at the 1900 Paris Exposition. Its lens was stationary, prefigured so as to sag into the correct shape. The telescope was aimed with the aid of a Foucault sidérostat, which is a movable plane mirror of diameter 2 m (6.56 feet), mounted in a large cast-iron frame. The horizontal tube was 60 m (197 feet) long and the objective had 1.25 m (4.1 feet) in diameter. The results were poor. When the year-long exposition was over, its builders were unable to sell it. It was ultimately broken up for scrap.

Paris 1900 exposition refractor

Issue #144

Astronomy Picture of the Day

2005 July 19

A Nearby Supernova in M51

Explanation: One of the nearest supernovas of recent years was discovered late last month in the bright nearby galaxy M51. It is visible on the right of the above before and after images of the picturesque spiral. Can you spot it? The supernova, discovered originally by Wolfgang Kloehr and now dubbed 2005cs, is still near its maximum brightness and visible with a telescope toward the constellation of the Hunting Dogs (Canes Venatici). The supernova has been identified as a Type II but has an unusual brightness history, creating speculation that is similar in nature to the brightest supernova of modern times: 1987A. The progenitor star has been identified as a bright blue star. Although hundreds of supernovas are discovered each year by automated searches, nearby supernova are rare and important because they frequently become bright enough to be studied by many telescopes and are near enough for their (former) host star and immediate surroundings to be spatially resolved. Supernova 2005cs may have left behind a core that has been compressed into a neutron star or black hole.

Credit & Copyright: R Jay GaBany (Cosmotography.com)

Astronomy Picture of the Day

2005 July 20

Water Ice in a Martian Crater

Explanation: What lies on the floor of this Martian crater? A frozen patch of water ice. The robotic Mars Express spacecraft took the above image in early February. The ice pocket was found in a 35-kilometer wide crater that resides 70 degrees north of the Martian equator. There, sunlight is blocked by the 300-meter tall crater wall from vaporizing the water-ice on the crater floor into the thin Martian atmosphere. The ice pocket may be as deep as 200 meters thick. Frost can be seen around the inner edge on the upper right part of the crater, while part of the lower left crater wall is bathed in sunlight. The existence of water-ice pockets inside craters near the Martian North Pole, like that pictured above and others noted previously, give clues not only about surface conditions in the Martian past but also possible places where future water-based astronauts might do well to land.

Credit: G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA;
Image created for and Copyright: Nature

Nordic Optical Telescope

The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. First light came in 1988, with regular observing beginning in 1989. It is funded by Denmark, Sweden, Iceland, Norway and Finland. Access is provided to astronomers of all nationalities through internation time allocation committees.

Looking down on the dome of the Nordic Optical Telescope, with the Atlantic Ocean behind.

The NOT was the first major telescope facility to use active optics to correct the shape of a thin, lightweight primary mirror.

The service building and dome of Nordic Optical Telescope situated above the clouds at the top of Roque de los Muchachos, La Palma.

The NOT is a 2.56 m telescope with the following instrumentation:

- ALFOSC -- CCD (visible light) faint object spectrograph and 4 Megapixel camera
- NOTCam -- 1 Megapixel HgCdTe Hawaii infrared camera and spectrograph
- MOSCA -- 16 Megapixel CCD camera
- SOFIN -- High resolution CCD spectrograph (up to R=170,000)
- StanCam -- Stand-by 1 Megapixel CCD camera
- LuckyCam -- High frame rate, low noise L3Vision CCD camera for lucky imaging
- TURPOL -- UBVRI Photopolarimeter

The interior of the telescope, showing an instrument on the Cassegrain focus

Issue #145

Astronomy Picture of the Day

2005 July 21

X-Ray Stars of 47 Tuc

Explanation: Visible light images show the central region of globular cluster 47 Tucanae is closely packed, with stars less than a tenth of a light-year apart. This Chandra false-color x-ray view of central 47 Tuc also shows the cluster is a popular neighborhood for x-ray stars, many of which are "normal" stars co-orbiting with extremely dense neutron stars -- stars with the mass of the Sun but the diameter of Manhattan Island. One of the most remarkable of these exotic binary systems is cataloged as 47 Tuc W, a bright source near the center of this image. The system consists of a low mass star and a a neutron star that spins once every 2.35 milliseconds. Such neutron stars are known to radio astronomers as millisecond pulsars, believed to be driven to such rapid rotation by material falling from the normal star onto its dense companion. In fact, x-ray observations of the 47 Tuc W system link this spin-up mechanism observed to operate in other x-ray binary stars with fast rotating millisecond pulsars.

Credit: C.Heinke (Northwestern U.) et al. CXC, NASA

Overwhelmingly Large Telescope

The Overwhelmingly Large Telescope (OWL) is a conceptual design by the European Southern Observatory organization for a telescope which is intended to have a single aperture of 100 meters in diameter.

Computer model of Overwhelmingly Large Telescope's external appearance.

Whilst this design would not exceed the angular resolving power of interferometric telescopes, it would have exceptional light-gathering and imaging capacity which would greatly increase the depth to which mankind could explore the universe.

If built, it would be the largest optical telescope ever constructed. It has been claimed that OWL would have more mirror surface than that of all previous professional telescopes put together.

All proposed designs for the OWL are variations on a segmented mirror, since there is no technology available to build a monolithic 100-meter mirror. The operation of a segmented mirror is somewhat more complicated than a monolithic one, requiring careful alignment of the segments (a technique called cophasing). Experience gained in existing segmented mirrors (for example, the Keck telescope) suggests that the mirror proposed for the OWL is feasible.

Issue #146

Astronomy Picture of the Day

2005 July 22

Tethys, Rings, and Shadows

Explanation: Seen from ice moon Tethys, rings and shadows would play across fantastic views of the Saturnian system. Haven't dropped in on Tethys lately? Then this gorgeous ringscape from the Cassini spacecraft will have to do for now. Caught in sunlight just below and left of picture center, Tethys itself is about 1,000 kilometers in diameter and orbits not quite five saturn-radii from the center of the gas giant planet. At that distance (around 300,000 kilometers) it is well outside Saturn's main bright rings, but Tethys is still one of five major moons that find themselves within the boundaries of the faint and tenuous outer E ring. Discovered in the 1980s, two very small moons Telesto and Calypso are locked in stable locations along Tethys' orbit. Telesto precedes and Calypso follows Tethys as the trio circles Saturn.

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

2MASS

Observations for the Two Micron All-Sky Survey (2MASS) began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres (Mt. Hopkins Arizona and Cerro Tololo/CTIO Chile, respectively) to ensure coverage of the entire sky. The most ambitious project to map the night sky to date, the final (post-processing) data release for 2MASS occurred in 2003. The whole sky was covered in three infrared wavebands around 2 µm (micrometres), J (1.25 µm), H (1.65 µm), and Ks (2.17 µm).

2MASS logo

General Information
Organization: UMass, IPAC (JPL/Caltech), NASA, NSF
Wavelength regime: IR (2 µm, 1.25 µm,1.65 µm, 2.17 µm)
Data source: two 1.3 m Cassegrain reflector equatorial mount telescopes (Mt. Hopkins, Tucson, AZ; Cerro Tololo, La Serena, Chile)
Survey goals: galaxies, brown dwarfs
Dataproducts: images, point source catalogue, extended object catalogue
Other names: Two Micron All-Sky Survey
Webpage:
About 2MASS
The catalogue of point sources
The catalogue of extended sources

The goals of this survey included:

- Detection of galaxies in the "zone of avoidance," a strip of sky obscured in visible light by our own Galaxy, the Milky Way.
- First detection of brown dwarfs.
- An extensive survey of low mass stars, the most common type of star both in our own galaxy and others.
- Cataloging of all detected stars and galaxies.

This last goal has been admirably achieved. Numerical descriptions of point sources (stars, planets, asteroids) and extended sources (galaxies, nebulae) were catalogued by automated computer programs to an average limiting magnitude of about 14. More than 300 million point sources and 1 million extended sources were catalogued. In November of 2003, a team of scientists announced the discovery of the Canis Major Dwarf Galaxy, at that time the closest known satellite galaxy to the milky way, based on analysis of 2MASS stellar data.

The resulting data and images from the survey are currently in the public domain, and may be accessed online for free by anyone at The Two Micron All Sky Survey at IPAC website (although interpretation and use of this data may require an advanced degree). There is also a list of 2MASS science publications with links to free pre-publication copies of the papers.

2MASS is sponsored by the University of Massachusetts (aka UMass, and the origin of the survey name), the Infrared Processing and Analysis Center (IPAC, run by JPL and Caltech), NASA, and the NSF.

Issue #147

Astronomy Picture of the Day

2005 July 23

Ringed Nebulae

Explanation: This gorgeous celestial vista is centered on one of the Milky Way's own planetary nebulae, M57, the famous Ring Nebula. The wide view is a composite of three exposures; one to record the details of the inner roughly one light-year span of the familiar nebula, one to record the surprisingly intricate but faint outer rings of glowing hydrogen gas, and one to pick up the rich assortment of distant background galaxies. By chance, one of the background galaxies, IC 1296 at the upper left, is close enough to show its barred, spiral structure making an attractive visual comparison with M57. Interestingly, though IC 1296 is 200 million light-years away compared to only 2 thousand light-years for M57, a faint ring is also apparent around the outer reaches of the distant spiral galaxy.

Credit & Copyright: Tony and Daphne Hallas

3C

The Third Cambridge Catalog of Radio Sources (3C) is an astronomical catalogue of celestial radio sources as measured at 159-MHz. It was published in 1959 by the Radio Astronomy Group of the University of Cambridge. References to entries in this catalogue use the prefix 3C followed by the entry number, with no space perforce. ie. 3C273. The catalogue was produced by the Cambridge Interferometer on the west side of Cambridge. (The interferometer had previously been used for the 2C survey, published in 1955).

The Catalogue was subsequently revised by Bennett in 1962, and for many years 3CR was considered as the definitive listing of the brighter radio sources in the Northern Hemisphere. The revision resulted in a number of sources being deleted from the catalogue (as being below the flux limit of 9Jy or as now-resolved blends of adjacent sources) and others being added. To avoid renumbering the existing sources (which were listed in RA order) these new sources were added using a decimal extension. Eg 3CR323.1 follows 3C323 in Right Ascension and precedes 3C324.

General Information
Organization: Radio Astronomy Group, University of Cambridge
Wavelength regime: 159-MHz radio
Data source: Mullard Radio Astronomy Observatory
Survey goals: First detailed survey of radio sources
Data products: 3C Catalogue
Webpage:
The Third Cambridge Catalog of Radio Sources

Issue #148

Astronomy Picture of the Day

2005 July 24

A Chicago Meteorite Fall

Explanation: If you wait long enough, a piece of outer space itself will come right to you. As Colby Navarro worked innocently on the computer, a rock from space crashed through the roof, struck the printer, banged off the wall, and came to rest near the filing cabinet. This occurred around midnight on March 26 in Park Forest, Illinois, USA, near Chicago. The meteorite, measuring about 10 cm across, was one of several that fell near Chicago that day as part of a tremendous fireball. Pictured above is the resulting hole in the ceiling, while the inset image shows the wall dent and the meteorite itself. Although the vast majority of meteors is much smaller and burn up in the Earth's atmosphere, the average homeowner should expect to repair direct meteor damage every hundred million years.

Credit & Copyright: Ivan and Colby Navarro

4C

The Fourth Cambridge Survey (4C) is an astronomical catalogue of celestial radio sources as measured at 178 MHz using the 4C Array. It was published in two parts, in 1965 (for declinations +20 to +40) and 1967 (declinations -7 to + 20 and +40 to +80), by the Radio Astronomy Group of the University of Cambridge. References to entries in this catalogue use the prefix 4C followed by the declination in degrees, followed by a period, and then followed by the source number on that declination strip, e.g. 4C-06.23.

The 4C Array, which used the technique of aperture synthesis, could reliably position sources of less than 2 Jy, to within about 0.35 arcmin in Right ascension and 2.5 arcmin in declination.

General Information
Organization: Radio Astronomy Group, University of Cambridge
Wavelength regime: 178 MHz radio
Data source: 4C Array, Mullard Radio Astronomy Observatory
Survey goals: Deep survey of radio sources
Dataproducts: 4C Catalogue
Webpage: The Fourth Cambridge Survey

Issue #149

Astronomy Picture of the Day

2005 July 25

Unusual Gas Filaments Surround Galaxy NGC 1275

Explanation: How were the unusual gas filaments surrounding galaxy NGC 1275 created? No one is sure. Galaxy NGC 1275 is the central dominant galaxy of the Perseus Cluster of Galaxies, a cluster with many member galaxies visible in the above image. In visible light, NGC 1275 appears to show a spectacular collision between two distinct galaxies. The galaxy and cluster are also bright emitters of X-rays. The unusual gas filaments are shown above in a very specific color of light emitted by hydrogen, here artificially colored pink. Possible origins for the filaments may involve details of the collision between the two galaxies, or alternatively, interactions between a galactic center black hole and the surrounding intracluster gas. NGC 1275, pictured above, spans about 100,000 light years and lies about 230 million light years distant toward the constellation of Perseus.

Credit & Copyright: C. Conselice (Caltech), WIYN, AURA, NOAO, NSF

5C

The Fifth Cambridge Catalog of Radio Sources (5C) is an astronomical catalogue of celestial radio sources as measured at 408-MHz and 1407-MHz. It was published in a number of parts between 1975 and 1995 by the Radio Astronomy Group of the University of Cambridge. The One-Mile Telescope used to produce this catalogue had an angular resolutions of 80 arcseconds and 23 arcseconds at 408 MHz and 1407 MHz respectively, and cataloged radio sources as faint as 2 milli-Janskys, considerably fainter than any previously cataloged radio source

References to entries in this catalogue use the prefix 5C followed by the catalogue part, a . and then the entry number, with no space perforce. ie. 5C12.311 for the 311th entry in part 12 of the 5C catalogue.

General Information
Organization: Radio Astronomy Group, University of Cambridge
Wavelength regime: 408-MHz and 1407-MHz radio
Data source: One-Mile Telescope, Mullard Radio Astronomy Observatory
Survey goals: Deep survey of radio sources
Dataproducts: 5C Catalogue
Webpage:
The 5C5 survey of radio sources
The 5C6 and 5C7 surveys of radio sources
The 5C12 survey near the North Galactic Pole
The 5C13 deep radio survey
The 5C14/5C15/5C16 Radio Survey at 408 and 1407 MHz

Issue #150

Astronomy Picture of the Day

2005 July 26

Hyperion: Sponge Moon of Saturn

Explanation: Why is Saturn's moon Hyperion textured like a sponge? Recent high-resolution images from the robot Cassini spacecraft orbiting Saturn show Hyperion to be an even stranger place than thought before. Previously, it was known that the length of a day on Hyperion is unpredictable. The moon's highly elliptical orbit around Saturn, its highly non-spherical shape, and its locked 4:3 orbital resonance with Titan torque Hyperion around so much it is hard to predict when the Sun will rise next. The newly imaged craters on the unusually coarse surface are surely the result of impacts, but for some reason have dark centers. The low density of Hyperion indicates it might even be a spelunker's paradise, riddled with tremendous caverns.

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

8C

The Eighth Cambridge Survey (8C) is an astronomical catalogue of celestial radio sources as measured at 38-MHz. It was published in 1990 by the Radio Astronomy Group of the University of Cambridge. Sources are labelled 8C HHMM+DDd where HHMM is the Right Ascension in hours and minutes, and DDd is the Declination in degrees and tenths of a degree, e.g. 8C 0014+861 for a source at Right Ascension 00 14 and 86.1 degrees Declination in 1950 coordinates.

General Information
Organization: Radio Astronomy Group, University of Cambridge
Wavelength regime: 38-MHz radio
Data source: Cambridge Low Frequency Synthesis Telescope, Mullard Radio Astronomy Observatory
Survey goals: Deep, low frequency survey of radio sources
Data products: 8C Catalogue
Webpage: The Rees 38-MHz survey

Issue #151

poon cho tang SG

Astronomy Picture of the Day

2005 July 27

America Returns to Space Flight

Explanation: NASA's launch of the massive Space Shuttle Discovery yesterday brought a nation known for its tremendous space program back to human space flight. Shuttle flights had been suspended for over two years previously following the tragic loss of the Space Shuttle Columbia crew on 2003 February 1. The complex, powerful Space Shuttle Discovery lifted a crew of seven into an Earth orbit that will bring them to the International Space Station (ISS). The shuttle crew will deliver supplies to the ISS, perform repairs, and test new methods for inspecting and repairing the shuttle's thermal protection system. Three space walks are planned. This Return to Flight Mission STS-114 is pictured above launching from Pad 39B in Cape Canaveral, Florida.

Credit: NASA

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9C

The Nineth Cambridge Catalog of Radio Sources (9C) is an astronomical catalogue of celestial radio sources as measured at 15-GHz. It was published in 2003 by the Cavendish Astrophysics Group of the University of Cambridge. The catalogue was originally made in order to locate radio sources which were interfering with observations using the Very Small Array, but the catalogue has also proved useful for other astronomical programs.

Sources are labelled 9C JHHMM+DDMM where HHMM+DDMM are the coordinates in the J2000 system, e.g. 9C J0934+2756.

General Information
Organization: Radio Astronomy Group, University of Cambridge
Wavelength regime: 15-GHz radio
Data source: Ryle Telescope, Mullard Radio Astronomy Observatory
Survey goals: Deep, high frequency survey of radio sources in the fields observed by the Very Small Array (VSA) telescope
Data products: 9C Catalogue and VSA source subtraction
Webpage: The 9C survey at 15GHz

Issue #152

poon cho tang SG

Astronomy Picture of the Day

2005 July 28

Spherical Planetary Nebula Abell 39

Explanation: Ghostly in appearance, Abell 39 is a remarkably simple, spherical nebula about five light-years across. Well within our own Milky Way galaxy, the cosmic sphere is roughly 7,000 light-years distant toward the constellation Hercules. Abell 39 is a planetary nebula, formed as a once sun-like star's outer atmosphere was expelled over a period of thousands of years. Still visible, the nebula's central star is evolving into a hot white dwarf. Although faint, the nebula's simple geometry has proven to be a boon to astronomers exploring the chemical abundances and life cycles of stars. In this deep image recorded under dark night skies, very distant background galaxies can be found -- some visible right through the nebula itself.

Credit & Copyright: Jim Misti (Misti Mountain Observatory)

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Astronomy Picture of the Day

2005 July 29

ISS and Discovery Transit the Sun

Explanation: That large sunspot near the right edge of the Sun is actually not a sunspot at all. It's the International Space Station (ISS) docked with the Space Shuttle Discovery on mission STS-114. In the past, many skygazers have spotted the space station and space shuttles as bright stars gliding through twilight skies, still glinting in the sunlight while orbiting 200 kilometers or so above the Earth's surface. But here, astronomer Anthony Ayiomamitis took advantage of a rarer opportunity to record the spacefaring combination moving quickly in silhouette across the solar disk on Thursday, July 28th from Athens, Greece. Launched on Tuesday, Discovery joined with the ISS Thursday, causing the already large space station seem to loom even larger.

Image Credit & Copyright: Anthony Ayiomamitis

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BeppoSAX

BeppoSAX was an Italian-Dutch satellite for X-ray astronomy. The satellite structure and control was built by various Italian and Dutch companies, while the scientific instruments were developed by the Italian CNR science research institute.

Artist's Conception of BeppoSax in Space. Credit: the Agenzia Spaziale Italiana (ASI) and the BeppoSAX Science Data Center (SDC)

General Information
Organization: ASI, NIVR
Wavelength regime: X-ray
Orbit height: 600 km
Orbit period: 96 min
Launch date: 30 April 1996
Deorbit date: 29 April 2003
Mass: 1,400 kg
Other names: Satellite per Astronomia X
Webpage: http://www.asdc.asi.it/bepposax/

Physical Characteristics
Telescope Style: 4 units of 30 grazing incidence nested coaxial and confocal mirrors
Diameter: 16.2 to 6.8 cm
Collecting Area: 150 cm² @ 6 keV (MECS), 22 cm² @ 0.25 keV (LECS)
Focal Length: 1.85 m

Instruments
MECS: 3 telescopes/proportional counters
LECS: telescope/proportional counter
HPGSPC: collimated proportional counter
PDS: 4 scintillation detectors
WFC: 2 cameras/proportional counters

BeppoSAX was named in honour of the Italian astronomer Giuseppe "Beppo" Occhialini. SAX stands for "Satellite per Astronomia i raggi X" or "Satellite for X-ray astronomy".

X-ray observations cannot be performed from ground-based telescopes, since Earth's atmosphere blocks most of the incoming radiation.

One of BeppoSAX's main achievements was the identification of numerous gamma ray bursts with extra-galactic objects.

Launched in 1996, the expected operating life of two years was extended to April 30, 2002. After this date, the orbit was decaying too rapidly and various subsystems were failing. Final deorbit was planned for 2003.

In April 29, 2003, the satellite ended its life falling into the Pacific Ocean.

Spacecraft characteristics

- Dimensions: 3.6 m high, 2.7 m diameter
- Solar cell power: 3 kW
- Data generated: 1 GB each orbit (90 min)

Intrumentation

BeppoSAX contained five science instruments:

- Low Energy Concentrator Spectrometer (LECS)
- Medium Energy Concentrator Spectrometer (MECS)
- High Pressure Gas Scintillation Proportional Counter (HPGSPC)
- Phoswich Detector System (PDS)
- Wide Field Camera (WFC)

The first four instruments (often called Narrow Field Instruments or NFI) point to the same direction, and allow observations of an object in a broad energy band of 0.1 to 300 keV (16 to 48,000 aJ).

The WFC contained two coded aperture cameras operating in the 2 to 30 keV (320 to 4,800 aJ) range and each covering a region of 20 by 20 degrees on the sky. The WFC was complemented by the shielding of PDS which had a (nearly) all-sky view in the 100 to 600 keV (16,000 to 96,000 aJ) band, ideal for detecting gamma ray bursts (GRB).

PDS shielding has poor angular resolution, but after a GRB was seen in the PDS, the position was refined first with the WFC. After this, follow-up observations with the NFI allowed accurate positioning of the GRB and detailed observations of the X-ray afterglow.

The MECS contained three indentical gas scintillation proportional counters operating in the 1.3 to 10 keV (208 to 1,602 aJ) range. LECS was almost identical to the MECS units, expect that it had a thinner window that allows photons with lower energies down to 0.1 keV (16 aJ) to pass through. High background contamination makes the LECS data above 4 keV (641 aJ) unusable. LECS and MECS had imaging capability, whereas the high-energy narrow field instruments were non-imaging.

HPGSPC was also a gas scintillation proportional counter, but high (three atmospheres) pressure. High pressure equals high density, and dense photon-stopping material allowed detection of photons up to 120 keV (19,000 aJ).

PDS was a crystal scintillator (natrium iodide / caesium iodide) capable of stopping photons up to 300 keV (48,000 aJ). The spectral resolution of PDS was rather modest when compared to the gas detectors.

Issue #153

poon cho tang SG

Astronomy Picture of the Day

2005 July 30

M106 in Canes Venatici

Explanation: Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial nebula was discovered in 1781 by the metric French astronomer Pierre Mechain. Later, it was added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe -- a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Youthful blue star clusters and reddish stellar nurseries trace the striking spiral arms of M106. Seen so clearly in this beautiful image, the galaxy's bright core is also visible across the spectrum from radio to x-rays, making M106 a nearby example of the Seyfert class of active galaxies. The bright core of a Seyfert galaxy is believed to be powered by matter falling into a massive central black hole.

Credit: Bernie and Jay Slotnick, Adam Block, AOP, NOAO, AURA, NSF

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Chandra X-ray Observatory

Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the mass limit for white dwarf stars to become neutron stars. "Chandra" also means "moon" or "luminous" in Sanskrit.

Artist's Illustration of the Chandra X-ray Observatory in Orbit (credit: NASA/MSFC)

General Information
Organization: NASA, SAO, CXC
Wavelength regime: X-ray
Orbit height: 10,000 km (perogee), 140,161 km (apogee)
Orbit period: 64 h and 18 min
Launch date: 23 July 1999
Mass: 4,800 kg
Other names: Advanced X-ray Astrophysics Facility, AXAF
Webpage: http://chandra.harvard.edu/

Physical Characteristics
Telescope Style: 4 nested pairs of grazing incidence paraboloid and hyperboloid mirrors
Diameter: 1.2 m
Collecting Area: 400 cm² at 1 keV
Focal Length: 10 m

Instruments
ACIS: imaging spectrometer
HRC: camera
HETGS: high resolution spectrometer
LETGS: high resolution spectrometer

Chandra Observatory is the third of NASA's four "Great Observatories". The first was Hubble Space Telescope; second the Compton Gamma Ray Observatory, launched in 1991; and last is the Spitzer Space Telescope. Prior to successful launch, the Chandra Observatory was known as AXAF, the Advanced X-ray Astronomical Facility.

Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes, requiring a space-based telescope to make these observations.

Discoveries

The data gathered by Chandra have greatly advanced the field of X-ray astronomy.

- The first light image, of supernova remnant Cassiopeia A, gave astronomers their first glimpse of the compact object at the center of the remnant, probably a neutron star or black hole.
- In the Crab Nebula, another supernova remnant, Chandra showed a never-before-seen ring around the central pulsar and jets that had only been partially seen by earlier telescopes.
- The first X-ray emission was seen from the supermassive black hole, Sagittarius A*, at the center of the Milky Way.
- Chandra found much cooler gas than expected spiralling into the center of the Andromeda Galaxy.
- Pressure fronts were observed in detail for the first time in Abell 2142, where clusters of galaxies are merging.
- The earliest images in X-rays of the shock wave of a supernova were taken of SN 1987A.
- Chandra showed for the first time the shadow of a small galaxy as it is being cannibalized by a larger one, in an image of Perseus A.
- A new type of black hole was discovered in galaxy M82, mid-mass objects purported to be the missing link between stellar-sized black holes and supermassive black holes.
- X-ray emission lines were associated for the first time with a gamma-ray burst, GRB 991216.
- High school students, using Chandra data, discovered a neutron star in supernova remnant IC 443.
- Observations by Chandra and BeppoSAX suggest that gamma-ray bursts occur in star-forming regions.
- Chandra data suggested that RXJ1856 and 3C58, previously thought to be pulsars, might be even denser objects: quark stars. These results are still debated.
- TWA 5B, a brown dwarf, was seen orbiting a binary system of Sun-like stars.
- Sound waves from violent activity around a supermassive black hole were observed in the Perseus Cluster.
- The X-ray shadow of Titan was seen when it transitted the Crab Nebula.

Technical description

Unlike optical telescopes which possess simple silvered parabolic surfaces (mirrors), X-ray telescopes generally have nested cylindrical paraboloid and hyperboloid surfaces coated with iridium. X-ray photons would be absorbed by normal mirror surfaces, so mirrors with a low grazing angle are necessary to reflect them. Chandra uses four pairs of nested mirrors, together with their support structure, called the High Resolution Mirror Assembly (HRMA).

Chandra's high elliptical orbit allows it to observe continuously for up to 55 hours of its 65 hour orbital period.

With an angular resolution of 0.5 arcsecond (2.4 µrad), Chandra possesses a resolution over one thousand times better than that of the first orbiting X-ray telescope, which had less precise gold-coated mirrors.

Instruments

The Science Instrument Module (SIM) holds the two focal plane instruments, the Advanced CCD Imaging Spectrometer (ACIS) and the High Resolution Camera (HRC), moving whichever is called for into position during an observation.

ACIS consists of 10 CCD chips and provides images as well as spectral information of the object observed. It operates in the range of 0.2 - 10 keV. HRC has two micro-channel plate components and images over the range of 0.1 - 10 keV. It also has a time resolution of 16 microseconds. Both of these instruments can be used on their own or in conjunction with one of the observatory's two transmission gratings.

The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. The High Energy Transmission Grating Spectrometer (HETGS) works over 0.4 - 10 keV and has a spectral resolution of 60-1000. The Low Energy Transmission Grating Spectrometer (LETGS) has a range of 0.09 - 3 keV and a resolution of 40-2,000.

History

In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to NASA by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the following year at Marshall Space Flight Center (MSFC) and the Smithsonian Astrophysical Observatory (SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telecope, Einstein (HEAO-2), into orbit. Work continued on the Chandra project through the 1980's and 1990's. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. Chandra's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle but put the observatory above the Earth's radiation belts for most of its orbit.

AXAF was renamed Chandra in 1998 and launched in 1999 by the shuttle Columbia (STS-93). It was the heaviest payload ever launched by the shuttle, a consequence of the Inertial Upper Stage booster rocket system needed to transport the spacecraft to its high orbit.

Chandra X-ray Observatory sits inside the payload bay on Space Shuttle Columbia mission STS-93.

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from MIT and Northrop Grumman Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope's focal plane during passages.

In 2004 Chandra celebrated its fifth year of operation.

Issue #154

poon cho tang SG

Astronomy Picture of the Day

2005 July 31

Solar System Object Larger than Pluto Discovered

Explanation: Is that a tenth planet? A faint, slowly moving dot discovered by computer shows clear signs of being a deep Solar System object at least as large as Pluto. The object, designated 2003 UB313, is currently situated nearly 100 times the Earth-Sun distance -- over twice the average Pluto-Sun distance. That far out, the only way a single round object could be as bright as 2003 UB313 would be if it is at least as large as Pluto and completely reflective. Since 2003 UB313 is surely not completely reflective, it could be substantially larger. One of the discovery frames is shown above digitally expanded and artificially brightened. 2003 UB313 was identified initially on frames taken by the automated 1.2-meter Samuel Oschin Telescope at Palomar Observatory in California, USA.

Credit: M. Brown (Caltech), C. Trujillo (Gemini), D. Rabinowitz (Yale), NSF, NASA

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Compton Gamma Ray Observatory

The Compton Gamma Ray Observatory (CGRO) was the second of the NASA "Great Observatories" to be launched to space, following the Hubble Space Telescope.

CGRO was launched on the Space Shuttle Atlantis, mission STS-37, on 5 April 1991. It was the heaviest astrophysical payload ever flown at that time. After one of its gyros failed, the observatory was deliberately de-orbited. NASA decided that a controlled crash was preferable, in the interest of public safety, to letting the craft come down on its own. It entered the Earth's atmosphere on 4 June 2000, with debris falling harmlessly into the Pacific Ocean.

Artist's Illustration of the Compton Gamma Ray Observatory in orbit (credit: NASA)

General Information
Organization: NASA
Wavelength regime: gamma ray
Orbit Height: 450 km
Orbit period: 90 min
Launch date: 5 April 1991
Deorbit date: 4 June 2000
Mass: 17,000 kg
Webpage: http://cossc.gsfc.nasa.gov/

Physical Characteristics
Telescope Style: scintillation detectors
Diameter: N/A
Collecting Area: varied by instrument
Effective Focal Length: N/A

Instruments
BATSE: all-sky monitor
OSSE: pointed detectors
COMPTEL: imaging telescope
EGRET: wide field telescope

CGRO carried a complement of four instruments that covered an unprecedented six decades of the electromagnetic spectrum, from 20 keV to 30 GeV. In order of increasing spectral energy coverage:

- Burst and Transient Source Experiment (BATSE) by NASA Marshall Space Flight Center searched the sky for short duration gamma ray bursts (20 to 600 keV) and conducted full sky surveys for long-lived sources. It consisted of 8 detectors.

- Oriented Scintillation Spectrometer Experiment (OSSE) by the Naval Research Laboratory detected gamma rays entering the field of view of any of four detectors, which could be pointed individually, in the 0.05 to 10 MeV range.

- Imaging Compton Telescope (COMPTEL) by Max Planck Institute and the University of New Hampshire was tuned to the 1-30 MeV energy range and determined the angle of arrival of photons to within a degree and the energy to within five percent at higher energies.

- Energetic Gamma Ray Experiment Telescope (EGRET) measured high energy (20 MeV to 30 GeV) gamma ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA Goddard Space Flight Center, Max Planck Institute, and Stanford University.

One great accomplishment of the CGRO was the discovery of terrestrial gamma ray sources in 1994 that come from thunderclouds.

The observatory was named after Dr. Arthur Compton, Nobel prize winner for work involved with gamma ray physics.

Issue #155

poon cho tang SG

Astronomy Picture of the Day

2005 August 1

2003 UB313: A Tenth Planet?

Explanation: Has a tenth planet been discovered? A newly discovered object, designated 2003 UB313 and located more than twice the distance of Pluto, is expected to be at least as large as Pluto and probably larger, given current measurements. 2003 UB313's dimness and highly tilted orbit (44 degrees) prevented it from being discovered sooner. Many astronomers speculate that numerous other icy objects larger than Pluto likely exist in the Kuiper Belt of the far distant Solar System. If so, and if some are found closer in than 2003 UB313, it may be premature to call 2003 UB313 the tenth planet. Illustrated above is an artist's drawing showing what 2003 UB313 might look. The unusually bright star on the right is the Sun. Much of the world eagerly await the decision by the International Astronomical Union on whether 2003 UB313 will be designated a planet or given a name without subscripts.

Illustration; Discovery Credit: M. Brown (Caltech), C. Trujillo (Gemini), D. Rabinowitz (Yale), NSF, NASA

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Astronomy Picture of the Day

2005 August 2

A Shuttle Back Flip at the Space Station

Explanation: Last week, crew members of the International Space Station (ISS) watched carefully as the Space Shuttle Discovery did a planned but unusual back flip upon approach. Discovery Commander Eileen Collins guided the shuttle through the flip, which was about 200 meters from the ISS when the above picture was taken. The ISS crew took detailed images of the dark heat shield tiles underneath during a 90-second photo shoot. The images are being analyzed to assess the condition of the dark heat shield. Later the shuttle docked with the space station. On the more usually photographed top side of the Space Shuttle, the above image shows Discovery's cargo bay doors open toward a distant Earth below.

Credit: ISS Expedition 11 Crew, STS-114 Crew, NASA

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Astronomy Picture of the Day

2005 August 3

The Busy Center of the Lagoon Nebula

Explanation: Stars are battling gas and dust in the Lagoon Nebula but the photographers are winning. Also known as M8, this photogenic nebula is visible even without binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M8 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. This spectacular portion of the Lagoon Nebula was created in scientifically-assigned colors from light emitted in very specific colors by hydrogen, silicon, and oxygen. The light from M8 we see today left about 5,000 years ago. Light takes about 50 years to cross this section of M8.

Credit & Copyright: Michael Sherick

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Gemini Observatory

The Gemini Observatory is an astronomical observatory consisting of 8-metre telescopes at two different sites. The Gemini telescopes were built and are operated by a consortium consisting of the United States, United Kingdom, Canada, Chile, Brazil, Argentina, and Australia. This partnership is managed by the Association of Universities for Research in Astronomy (AURA), and the headquarters of the observatory are located in Hilo, Hawaii.

Gemini Observatory. This time exposure shows the stars of the South Celestial Pole circling over Gemini South with the Large Magellanic Cloud visible as a faint "smudge" at the upper left. Motion of the Gemini Enclosure (dome) is also visible during the course of this 45 minute exposure.

General Information
Organization: AURA
Location: Mauna Kea, Hawai'i; Cerro Pachón, Chile
Coordinates: 19°49' N 155°28' W; 30°13' S 70°43' W
Altitude: 4,200 m; 2,500 m
Webpage: Gemini Observatory

Telescopes
Gemini North: 8.1 m Cassegrain reflector
Gemini South: 8.1 m Cassegrain reflector

One telescope (Gemini North, also called the Frederick C. Gillett telescope) is located on Hawaii's Mauna Kea. Its location makes for excellent viewing conditions due to the superb atmospheric conditions on top of the over 4,200 m (13,800 ft) high dormant volcano. It saw first light in 1999 and began scientific operations in 2000.

The other (Gemini South) is located at over 2,500 m (9,000 ft) elevation on a mountain in the Chilean Andes called Cerro Pachón. Very dry air and negligible cloud cover make this another prime telescope location (shared by several other observatories, including the SOAR Telescope and Cerro Tololo Inter-American Observatory). Gemini South saw first light in 2000.

The Gemini Observatory's international headquarters is located in Hilo, Hawaii at the University of Hawaii at Hilo's University Park.

Together, the twin Gemini telescopes provide complete unobstructed coverage of both the northern and southern skies. They are currently the among the largest and most advanced optical/infrared telescopes available to astronomers. Both employ a range of advanced technologies to deliver the highest quality images, including laser guide stars, adaptive optics and multi-object spectroscopy. In addition, the two telescopes allow very high-quality infrared observations due to the advanced protected silver coating of their mirrors and advanced ventilation systems. Thanks to a high degree of networking, the Gemini telescopes can be operated remotely, and observations can be run when atmospheric conditions suit them best, reducing unnecessary travel by astronomers.

It is estimated that the two telescopes cost approximately $184 million to construct, and a night on each Gemini telescope costs about $33,000.

Issue #156

poon cho tang SG

Astronomy Picture of the Day

2005 August 4

Stars Young and Old

Explanation: Galactic or open star clusters are relatively young swarms of bright stars born together near the plane of our Milky Way Galaxy. Separated by about a degree on the sky, two nice examples are M46 (upper left) 5,400 light-years in the distance and M47 (lower right) only 1,600 light-years away toward the nautical constellation Puppis. Around 300 million years young M46 contains a few hundred stars in a region about 30 light-years across. Aged 80 million years, M47 is a smaller but looser cluster of about 50 stars spanning 10 light-years. But this portrait of stellar youth also contains an ancient interloper. The small, colorful patch of glowing gas in M46 is actually the planetary nebula NGC 2438 - the final phase in the life of a sun-like star billions of years old. NGC 2438 is estimated to be only 3,000 light-years distant and likely represents a foreground object, only by chance appearing along our line of sight to youthful M46.

Credit & Copyright: Chris Hetlage

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INTEGRAL

The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.

Artist's Illustration of INTEGRAL in orbit (credit: ESA)

General Information
Organization: ESA, NASA, RKA
Wavelength regime: gamma ray
Orbit Height: 9,000 km (perigee), 153,000 km (apogee)
Orbit period: 72 hr
Launch date: 17 October 2002
Mass: 4,000 kg
Webpage: http://www.esa.int/SPECIALS/Integral/

Physical Characteristics
Telescope Style: coded mask
Diameter: 3.7 m
Collecting Area: 500 cm2 (SPI and JEM-X), 3,100 cm2 (IBIS)
Effective Focal Length: N/A

Instruments
SPI: spectrometer
IBIS: imager
JEM-X: X-ray monitor
OMC: optical monitor

INTEGRAL is an ESA mission in cooperation with the Russian Space Agency and NASA. It has had some notable successes, for example in detecting a mysterious 'iron quasar'. It has also had great success in investigating gamma-ray bursters and evidence for black holes. INTEGRAL's orbit has a period of roughly 72 hours, and has a high eccentricity, with perigee close to the Earth at 10,000 km, within the magnetospheric radiation belt. However, most of each orbit is spent outside this region, where scientific observations may take place. It reaches a furthest distance from Earth (apogee) of 153,000 km. It is controlled from ESOC in Darmstadt, Germany, ESA's control centre.

Issue #157

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Astronomy Picture of the Day

2005 August 5

HD 188753: Triple Sunset

Explanation: Although it looks like fiction, this artist's vision of sunset on an alien world is based on fact -- the recent discovery of a hot, jupiter-sized planet orbiting in triple star system HD 188753. Only 149 light-years away in the constellation Cygnus, HD 188553's massive planet was detected by astronomer Maciej Konacki after analyzing detailed spectroscopic data from the Keck Observatory. The large planet itself is depicted at the upper left in this imagined view from the well-illuminated surface of a hypothetical rocky moon. From this perspective, the closest, hottest and most massive star in the triple system, a star only a little hotter than the Sun, has set below distant peaks. The two other suns nearing the horizon are both cooler and farther from the large planet. While other hot, jupiter-like planets are known to orbit nearby stars, the "crowded" multiple star nature of this system challenges current theories of planet formation.

Illustration Credit: courtesy JPL-Caltech, NASA

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IRAS

The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths.

Launched in January 25, 1983, its mission lasted ten months. It was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC).

Artist's concept of the IRAS satellite.

General Information
Organization: NASA, NIVR, SERC
Wavelength regime: infrared
Orbit: sun-synchronous
Launch date: 25 Jan 1983
Deorbit date: 21 Nov 1983
Coolant: 720 L (77 kg) of superfluid He
Webpage: http://lambda.gsfc.nasa.gov/product/iras

Physical Characteristics
Diameter: 0.57 m
Collecting Area: ~1 m²
Focal Length: 5.5 m, f/9.6

Instruments
Main survey instrument: array of 65 detectors
Low Resolution Spectrometer (LRS): 822 µm slitless spectrometer
Chopped Photometric Channel (CPC): low-quality mapping

IRAS mapped 96% of the sky four times, at 12, 25, 60 and 100 micrometre wavelengths, with resolutions ranging from 0.5' at 12 micrometers to 2' at 100 micrometers. It discovered about 500,000 sources, many of which are still awaiting identification. About 75,000 of those are believed to be starbust galaxies, still enduring their star-formation stage. Many other sources are normal stars with disks of dust around them, possibly the early stage of a planetary system formation. New discoveries included a dust disk around Vega and the first images of the Milky Way Galaxy's core.

IRAS's life, like most of infrared satellites, was limited by its cooling system: to effectively work in the infrared domain, a satellite must be cooled to impressively low temperatures. In IRAS' case, 720 liters of superfluid helium kept the satellite at a temperature of 1.6 kelvins (about -272 °C). The fluid keeps the satellite cool by evaporation. When the fluid totally evaporated, the satellite temperature rose preventing further observations.

Today (2004), the Spitzer Space Telescope is the best infrared telescope, allowing astronomers to follow up many detections first made by IRAS.

In addition to its main work, IRAS also discovered three asteroids, including notably 3200 Phaethon (an Apollo asteroid and the parent body of the Geminid meteor shower), as well as the periodic comet 126P/IRAS.

Asteroids discovered: 3
- 3200 Phaethon on October 11, 1983
- 3728 IRAS on August 23, 1983
- 10714 1983 QG on August 31, 1983

Issue #158

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