Astronomy fanatica
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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 -
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 The catalogue was originally made in order to locate radio sources which were interfering with observations using the Very Small Array, but the catalogue has also proved useful for other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 -
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) -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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 -
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): 8–22 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 -
Astronomy Picture of the Day
2005 August 6
Raining Perseids
Explanation: Comet dust rained down on planet Earth last August, streaking through dark skies in the annual Perseid meteor shower. So, while enjoying the anticipated space weather, astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of August 11/12 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Although the comet dust particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bruenjes notes that there are 51 Perseid meteors in the composite image, including one seen nearly head-on. This year, the Perseids Meteor Shower will peak in the early morning hours on Friday, August 12.
Credit & Copyright: Fred Bruenjes -
James Webb Space Telescope
The James Webb Space Telescope (JWST) is a planned orbital infrared observatory, intended (in part) to replace the aging Hubble Space Telescope. It will be jointly constructed and operated by ESA and NASA. Formerly called the Next Generation Space Telescope (or NGST), it was renamed after NASA's second administrator, James E. Webb, in 2002. The telescope's launch is planned for 2011.
James Webb Space Telescope
General Information
Organization: NASA, ESA, CSA
Wavelength regime: infrared
Orbit height: 1.5×10^6 km from Earth (L2 Lagrangian point)
Orbit period: 1 year
Launch date: (August 2011)
Deorbit date: (2016 - 2021)
Mass: 6,200 kg
Other names: Next Generation Space Telescope
Webpage: http://www.jwst.nasa.gov
Physical Characteristics
Telescope Style: (refractor, Newtonian reflector, etc.)
Diameter: ~6.5 m
Collecting Area: 25 m²
Instruments
NIRCam: Near IR Camera
NIRSpec : Near IR Spectrograph
MIRI: Mid IR Instrument
FGS: Fine Guidance Sensors
Mission
The JWST's primary mission is to examine the infrared remnants of the big bang, and thus to make observations of an earlier state of the universe than is possible today. To achieve this, sensors of unparalleled sensitivity will be used, which in turn requires that the entire spacecraft be particularly cold, and that major sources of IR interference (notably the Sun, the Earth, and the Moon) be blocked. To this end, JWST will be accompanied by a large metalized fanfold sunshield, which will unravel to block infrared radiation from these sources. The telescope's lagrangian orbit (see below) ensures that the Earth and Sun occupy the same relative position in the telescope's view, and thus make the operation of this shield possible.
Optics
Although JWST has a planned weight half that of the Hubble, its primary mirror (a 6.5 meter beryllium reflector) is more than 5 times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 segments, which will unfold after the telescope is launched. Sensitive micromotors and wavefront sensors will position the mirror segments in the correct location, but subsequent to this initial configuration they will only rarely be moved; unlike terrestrial telescopes like the Keck which continually adjust their mirror segments using active optics to overcome the effects of gravitational loading and wind loading.
Current Status
Funding difficulties caused partly by the increased cost of JWST and of other NASA missions such as for Mars exploration and potential servicing of the Hubble Space Telescope mean that the JWST mission is likely to be reduced in scope. The proposed descope of the JWST from 6.5m to 4m has been abandoned, but other cost-cutting measures are still on the table.
Construction & Engineering
Northrop Grumman Space Technology serves as the primary contractor for the development and integration of the Observatory. They are responsible for developing and building the Spacecraft, which includes both the spacecraft bus and sunshield. Ball Aerospace has been subcontracted to develop and build the Optical Telescope Element (OTE). Goddard Space Flight Center is responsible for providing the Integrated Science Instrument Module (ISIM).
For the present architecture, the ISIM contains four science instruments. The primary instrument of the Observatory, the NIRcam (Near InfraRed Camera), will be built by a team led by the University of Arizona, with Principal Investigator Dr. Marcia Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center located in Palo Alto, California.
Issue #159 -
Astronomy Picture of the Day
2005 August 7
Dueling Auroras
Explanation: Will it be curtains for one of these auroras? A quick inspection indicates that it is curtains for both, as the designation "curtains" well categorizes the type of aurora pattern pictured. Another (informal) type is the corona. The above auroras resulted from outbursts of ionic particles from the Sun during the last week of 2001 September. A polarity change in the solar magnetic field at the Earth then triggered auroras over the next few days. The above picture was taken on 2001 October 3 as fleeting space radiation pelted the Earth's atmosphere high above the Yukon in Canada.
Credit & Copyright: Phil Hoffman -
New General Catalogue
The New General Catalogue (NGC) is the most well-known catalogue of deep sky objects in amateur astronomy. It contains nearly 8,000 objects, known as the NGC objects. The NGC is one of the largest comprehensive catalogues, as it includes all types of deep sky objects (not specialised to just galaxies for instance).
Spiral Galaxy NGC 3982 displays numerous spiral arms filled with bright stars, blue star clusters, and dark dust lanes. It spans about 30,000 light years, lies about 60 million light years from Earth and can be seen with a small telescope in the constellation of Ursa Major.
The catalogue was compiled in the 1880s by J. L. E. Dreyer using observations mostly from William Herschel, and then subsequently expanded with two Index Catalogues (IC I & IC II), adding nearly 5,000 objects.
Objects in the southern sky are somewhat less well catalogued but many were observed by John Herschel. The NGC contained many errors which have for the most part been eliminated by the Revised NGC.
General Information
Organization: William Herschel, Dunsink Observatory, Royal Astronomical Society, revised by Sulentic and Tifft
Wavelength regime: Visible (naked eye)
Data source: William Herschel, Birr Castle telescope and Dunsink Observatory
Survey goals: Survey of non-stellar objects
Data products: NGC Catalogue
Webpage: The Revised New General Catalogue
Issue #160 -
Astronomy Picture of the Day
2005 August 8
Mars to Appear Normal This August
Explanation: Will Mars appear extremely close and bright later this month? No. Regardless of numerous urban legends circulating, Mars will a relatively normal August. October is the best month to see Mars this year. The red planet is now visible in the morning before sunrise. As Earth catches up to Mars in their respective orbits around the Sun, Mars will keep rising earlier in the night. On 2005 October 30, Earth will have caught up to Mars and the planets will be the nearest to each other in their orbits -- this time around. On October 30, Mars will be nearly opposite to the Sun, rise at sunset, set at sunrise, and appear highest and brightest around midnight. Also on October 30, Mars will appear brighter than it has in the past two years, although still over 10,000 times smaller and fainter than the full Moon. Earth will then pass Mars, and Mars will appear to fade. Pictured above, Mars is shown as it appeared 2003 August 27, when it appeared slightly brighter than it had in nearly 60,000 years. The foreground setting is in the Valley of Fire state park in Nevada, USA. The ellipticity of orbits primarily determines the closeness and brightness of Mars during opposition.
Credit & Copyright: Wally Pacholka (Astropics.com) -
Spitzer space telescope
The Spitzer Space Telescope (SST) (formerly the Space Infrared Telescope Facility (SIRTF)) is an infrared space observatory, the fourth and final of NASA's Great Observatories.
The duration of the mission will be a minimum of 2.5 years, with 5 or more optimal. In keeping with NASA tradition, the telescope was renamed after successful demonstration of operation, on December 18, 2003. Unlike most telescopes which are named after famous deceased astronomers by a board of scientists, the name for SIRTF was obtained from a contest open only to children (to the delight of science educators).
Spitzer Space Telescope, artist's concept against IR Milky Way.
General Information
Organization: NASA, JPL/Caltech
Wavelength regime: infrared
Orbit: 8.7×10^6 km (5.4×10^6 mi) (heliocentric, trailing Earth at L5)
Launch date: August 25, 2003
Deorbit date: circa 2008
Mass: 950 kg (2,090 lb)
Other names: Space Infrared Telescope Facility, SIRTF
Webpage: spitzer.caltech.edu
Physical Characteristics
Telescope Style: Lightweight beryllium, cooled below 5.5 K
Diameter: 85 cm
Collecting Area: 2.3 m²
Focal Length: f/12
The name chosen was after Dr. Lyman Spitzer, Jr., one of the 20th century's most influential scientists. In the mid-1940s, he first proposed placing telescopes in space.
The US$670 million SST was launched on Monday 25 August 2003 at 1:35:39 (EDT) from Cape Canaveral Air Force Station on a Delta II 7920H ELV rocket. It follows a rather unusual orbit, heliocentric instead of geocentric, following earth in its orbit, and drifting away from the earth at approximately 0.1 astronomical unit per year. The primary mirror is 85 cm in diameter, f/12 and made of beryllium and cooled to 5.5 K. The satellite contains three instruments that will allow it to perform imaging and photometry from 3 to 180 micrometres, spectroscopy from 5 to 40 micrometres, and spectrophotometry from 5 to 100 micrometres.
The Spitzer Space Telescope Facility launches from Cape Canaveral Air Force Station in Florida on Monday, Aug. 25, 2003, at 1:35 a.m. EDT (Sunday, August 24, at 10:35 p.m. PDT).
The SST is the only one of the Great Observatories not launched by the Space Shuttle. It was originally intended to; after the Challenger disaster, the Centaur LH2/LOX upper stage that would have been required to push it into its intended orbit was banned from Shuttle use.
Instruments
- IRAC (Infrared Array Camera), a infrared camera which operates simultaneously on four wavelengths (3.6 µm, 4.5 µm, 5.8 µm and 8 µm). The resolution is 256 x 256 pixels.
- IRS (Infrared Spectrograph), a infrared spectrometer with four sub-modules which operates at the wavelengths 5.3 µm-14 µm (low resolution), 10 µm-19.5 µm (high resolution), 14 µm-40 µm (low resolution), and 19 µm-37 µm (high resolution).
- MIPS (Multiband Imaging Photometer for Spitzer), three detector arrays in the far infrared (128 x 128 pixels at 24 µm, 32 x 32 pixels at 70 µm, 2 x 20 pixels at 160 µm)
Earlier infrared observations had been made by both space-based and ground-based observatories. Ground-based observatories have the drawback that at infrared wavelengths or frequencies, both the Earth's atmosphere and the telescope itself will radiate (glow) strongly. This necessitates lengthy calibrations of all images and will decrease the ability to detect faint objects. Previous space-based satellites (such as IRAS, the Infrared Astronomical Satellite) were operational during the 1980s and great advances in astronomical technology have been made since then.
Results
The first images taken by SST were designed to show off the abilities of the telescope and showed a glowing stellar nursery; a swirling, dusty galaxy; a disc of planet-forming debris; and organic material in the distant universe. Since then, monthy press releases have shown off Spitzer's capabilities, as the Hubble Heritage images do for the HST. As one of its most noteworthy observations, in 2005, SST became the first to directly capture the light from extrasolar planets; the "hot Jupiter" planets HD 209458b and TrES-1 respectively. This was the first time extrasolar planets had actually been visually seen, and earlier observations had been indirectly made by drawing conclusions from behaviors of the star the planets were orbiting.The telescope also discovered in April 2005 that Cohen-kuhi Tau/4 had a planetary disk that was vastly younger and contained less mass than previously theorized leading to new understandings of how planets are formed.
While some time on the telescope is reserved for participating institutions and crucial projects, astronomers around the world also have the opportunity to submit proposals for observing time. Important targets include forming stars (young stellar objects, or YSOs), planets, and other galaxies. Images are freely available for educational and journalistic purposes.
Clockwise from the upper-left: Infrared views of spiral galaxy Messier 81; Embedded outflows from Herbig-Haro 46/47 protostar; Protostars uncovered in multiple views of dark globule in IC1396; and Comet Schwassmann-Wachmann 1.
Spitzer spotted a faintly glowing body in that may be the youngest star ever seen. The telescope was trained on a core of gas of dust known as L1014 which had perviously appeared completely dark to ground based observatories and to the ISO (Infrared Space Observatory), predecessor to Spitzer. The advanced technology of Spitzer revealed a bright red hot spot in the middle of L1014.
Scientists from the University of Texas who discovered the object believe the hot spot to be an example of early star development with the young star collecting gas and dust from the cloud around it. Early speculation about the hot spot was that it might have been the faint light of another core that lies 10 times further from Earth but along the same line of sight as L1014. Follow-up observation from ground-based near infrared observatories detected a faint fan-shaped glow in the same location as the object found by Spitzer. That glow is too feeble to have come from the more distant core leading to the conclusion that the object is located within L1014. (Young, et al., 2004)
Valentine's Day release: These bright young stars are found in a rosebud-shaped (and rose-colored) nebulosity known as NGC 7129. The star cluster and its associated nebula are located at a distance of 3300 light-years in the constellation Cepheus.
Issue #161 -
Astronomy Picture of the Day
2005 August 9
The Belt of Venus over Elwood Beach
Explanation: Although you've surely seen it, you might not have noticed it. During a cloudless twilight, just before sunrise or after sunset, part of the atmosphere above the horizon appears slightly off-color, slightly pink. Called the Belt of Venus, this off-color band between the dark eclipsed sky and the blue sky can be seen in nearly every direction including that opposite the Sun. Straight above, blue sky is normal sunlight reflecting off the atmosphere. In the Belt of Venus, however, the atmosphere reflects light from the setting (or rising) Sun which appears more red. The Belt of Venus can be seen from any location with a clear horizon. Pictured above, the Belt of Venus was photographed behind Elwood Beach in Melbourne, Australia. The belt is frequently caught by accident in other photographs.
Credit & Copyright: Russell Cockman -
Astronomy Picture of the Day
2005 August 10
The Heart and Soul Nebulas
Explanation: Is the heart and soul of our Galaxy located in Cassiopeia? Possibly not, but that is where two bright emission nebulas nicknamed Heart and Soul can be found. The Heart Nebula, officially dubbed IC 1805 and visible above on the right, has a shape reminiscent of a classical heart symbol. Both nebulas, shown above in false color, shine brightly in the light of energized hydrogen. Several young open clusters of stars populate the image and are visible above in and around the nebula centers. Light takes about 6,000 years to reach us from these nebulas, which together span roughly 300 light years. Studies of stars and clusters like those found in the Heart and Soul Nebulas have focussed on how massive stars form and how they affect their environment.
Credit & Copyright: Richard Crisp (narrowbandimaging.com)
