Tuesday, September 13, 2005
Hayabusa Spacecraft Asteroid Rendezvous. Supernova Champ Catches 40th Prize.
I decided that today you won't get any musings about John Roberts and his continuing effort to avoid answering any real questions (or Senator Biden's grandstanding) during his confirmation hearings. Nor will I rant about the Bungler in Chief and his painfully obvious shortcomings in dealing with the aftermath of Hurricane Katrina. I'm not even going to subject you to the roller coaster ride that is the Boston Red Sox. Today's post is dedicated to the stars, and my material comes from the Sky and Telescope web site.
Hayabusa Spacecraft Arrives at Asteroid Itokawa
September 12, 2005 After a series of programmatic setbacks, including the recent loss of a key instrument on the Suzaku X-ray observatory, Japanese space scientists finally have something to cheer about. This morning at 1:00 Universal Time, at a point some 320 million kilometers (200 million miles) from Earth, a spacecraft named Hayabusa reached asteroid 25143 Itokawa and eased into position just 20 kilometers away from it.
For the next two weeks the spacecraft will maintain its 20-km standoff distance on the asteroid's sunlit side, moving inward to just 7 km away by month's end, to map the entire surface as Itokawa slowly rotates every 12.1 hours. In addition to its Asteroid Multiband Imaging Camera (AMICA), which records light at seven visible and infrared wavelengths, Hayabusa carries a laser altimeter to measure surface heights and two spectrometers to analyze mineral compositions. Initial images from the camera show that Itokawa is about 600 meters long and very elongated, appearing much as expected from ground-based scrutiny.
The spacecraft will also deploy a small lander, called Minerva, designed to hop from spot to spot for a few days and view the landscape with three cameras. Hayabusa should make it back to Earth in June 2007, when its sample container, sealed to protect its thimbleful of asteroid, will plunge through the atmosphere and parachute into the Australian Outback.
Itokawa is an Apollo-type asteroid whose orbit crosses that of Earth over time and thus represents a potential impact threat. Its 1.5-year orbit frequently brings it near the Earth most recently in 2001 and 2004, when observatories and radar antennas studied it intensively.
We are learning more and more about these flying mountains, and it's long overdue, as the information in the last paragraph of the excerpt points out. Earth crossing asteroids and comets are abundant, and it is only a matter of time before one of these objects strikes our planet. In recent years, we have obtained a growing catalogue of these objects, and missions like this one will help us to determine how to best deal with the threat they pose.
Supernova Champ Makes 40th Find
September 2, 2005 On the night of August 4th, legendary supernova hunter Robert O. Evans made his 40th visual discovery of a supernova, a world record. Evans spotted and recognized the new, 14th-magnitude star in the barred spiral galaxy NGC 1559 using his 12-inch Newtonian reflector and his prodigious memory for star fields.
Evans observes from his backyard in Hazelbrook, New South Wales, about 100 kilometers (70 miles) west of Sydney. He searches for supernovae by memorizing the fields of galaxies. He has committed more than 1,000 galaxies and their environs to heart down to magnitude 15, so that he can check each field rapidly and systematically just by eye.
Evans made his first official find in 1981. "Of the 40 visual discoveries," he writes, "10 were found with my 10-inch reflector; 18, I think, with my 16-inch; 3 with the 40-inch telescope at Siding Spring Observatory; and the rest with the 12-inch that I now use here at home."
In addition, Evans has found five more supernovae and a comet on photographs: four of the supernovae and the comet on UK Schmidt plates as part of a professional-amateur search effort, and one on ESO Red Survey plates. Designated SN 2005df, his latest supernova was soon determined to be of Type Ia, caught a few days before it attained its maximum brightness.
Type Ia explosions happen in a close binary-star system where a white dwarf, accreting matter from its companion star, reaches critical mass, becomes unstable, and starts to shrink. In a matter of seconds its material undergoes a complete thermonuclear runaway reaction. The catastrophic explosion can, for a few days, outshine its entire host galaxy.
While on a three-week work assignment in North Ryde, NSW, Australia (about a 30-minute drive west of Sydney) in late January-mid February, I had the good fortune to see a science program on the local television station detailing Evans's career as an observer. His performance is nothing short of astounding given the tools he uses to watch the skies. As the larger observatories get more and more involved with observing various objects in different portions of the spectrum with instruments that are becoming more and more exotic, it has fallen to "backyard" astronomers to make visual discoveries like the ones Evans has made.
The type Ia designation is an important one because we have two nearby stellar neighbors, Sirius, the brightest star, and Procyon that have close white dwarf companions. Sirius in Canis Major, and Procyon in Canis Minor are 8.6 and 11.4 light-years away from us, and are two of the closest star systems to our solar system. To get an idea about whether our proximity to these systems places us in danger, the 1991 novel Supernova by Roger MacBride Allen and Eric Kotani takes a speculative look at what might happen if the Sirius system underwent such an explosion.
Every northern hemisphere astronomer, whether a professional or an amateur should take at least one trip south of the equator to view the parts of the sky that are hidden by Earth's curvature. My stay occurred during the southern hemisphere summer, and to see familiar winter constellations like Orion, Taurus and Gemini hanging low in the northern sky "upside down" was a lesson in perspective (as was the upside down Moon!). Gone were the familiar Big Dipper and Little Dipper, Cassiopeia and Cepheus.
Conversely, to look at the southern circumpolar stars of Centaurus, Carina and the Southern Cross was the icing on the cake of my stay in Australia (in addition to Sydney Harbor, Manly Bay, the Sydney Cricket Grounds, Macquarie Centre...but I digress). Armed with a pair of Canon 10x50 binoculars, I was treated to the richness of the deep southern part of the Milky Way--a part of the sky that is now invisible to me as I gaze south from my yard to see the sky end at Scorpius and Sagittarius. To close this post, I salute Mr. Robert Evans. Cheers to you sir!