August 2004 night skies
After a long absence, humans have returned to Saturn in the form of the Cassini robotic spacecraft and its piggyback lander, Huygens. During its four-year mission, Cassini will orbit Saturn at least seventy-six times times taking all types of measurements and pictures of the planet and many of its moons. Hopefully these measurements and images will help solve the mysteries of the ringed planet.
Of primary interest is when and how the planet’s rings formed. Most theories have told us that the rings would not last very long and would soon be consumed by the planet. On June 30, Cassini passed through the rings twice during a ninety-six-minute engine burn to enter orbit around the planet. The probe will never be as close to the rings again. To play it safe, Cassini turned is large, hardened antenna forward to protect the body from damage as it skipped through a large gap in the rings.
After analysis of the data during the engine burn, scientists saw what amounted to a horrific “hail storm” of small particles. Cassini was peppered by microscopic bits of dust that slammed into it at about forty-five thousand miles per hour. At the peak, 680 bits per second pummeled the probe, according to NASA. The particles are believed to be about the size of cigarette smoke.
Though it has been known for years that the rings are mostly water ice, Cassini’s pass showed that the rings are dirtier than expected. So, what is mixed in with the ice? Nobody knows what the other stuff is made of, but NASA scientists think it is likely silicates and organic material, the stuff of rocks and dirt on Earth. The ice is also thought to contain water mixed with other frozen substances such as ammonia.
There are two reasons to believe the rings are young: First, they are bright and shiny like something new. The wide-spanning rings sweep up space dust as Saturn orbits the Sun. Rings much older than a few hundred million years would be darkened by accumulated dust. Second, small moons that orbit through the outermost regions of the ring system are gaining angular momentum at the expense of the rings. During the next few hundred million years, the outer halves of the rings are expected to fall toward the planet, and the little moons—called shepherd satellites—will be flung into interplanetary space.
Hopefully, Cassini will solve other ring-mysteries, as well. In the early ‘80s, the Voyager spacecraft passed by and took close-up pictures that revealed many strange things in the rings, including spokes, braids, and waves. Some of the waves have a spiral shape, like the spiral arms of galaxies. To an astronaut floating among the rings, such waves would appear to be gentle swells a few kilometers high and hundreds of kilometers wide. They move around the rings every few days or weeks. The spiral waves have a good explanation: they are the result of gravitational tugs from Saturn's moons, the same ones that are sapping the rings' angular momentum. Other structures, like spokes and irregular ripples, are still a bit puzzling. Some of them might be signs of space rocks plunging through the ring system. Others might be spawned by tiny moonlets, as yet undiscovered, floating within Saturn's rings.
Stay tuned in early 2005 as the seven-hundred-pound Huygens probe parachutes to the surface of Saturn’s largest moon, Titan, which is larger than the planet Mercury. There it will report from Titan's surface for as brief as three minutes or as long as a half hour, according to NASA. Little is known of Titan's surface, but the recent Keck and Hubble images have given us a few insights. It could be composed of hard rock and have hydrocarbon seas or large areas covered with ethane or methane ice and snow. Huygens should last long enough to send back a few pictures and make measurements of the atmosphere and what ever it lands upon.
Comet Swift-Tuttle made its most recent pass through the inner solar system nearly ten years ago, in December 1992, laying down more bits of dust that create the Perseid meteor shower each August. Swift-Tuttle’s orbit is highly elongated and it takes roughly 130 years to make one trip around the Sun. Well-known meteor astronomer Esko Lyytinen, of Finland, suggests that the Perseids may provide some surprises this year. He has made calculations concerning extra-dense filaments of material trailing well behind the comet. He concludes that the Perseids may put on an unusually strong display in 2004. Lyytinen believes Earth will pass within 112,000 miles of the center of this debris trail left by comet Swift-Tuttle during its 1862 visit. Most of Europe and western Asia will have the best chance of viewing this unusual Perseid shower which peaks on August 11.
In 2028, Lyytinen expects an even more dramatic Perseid display as the Earth passes to within thirty-seven thousand miles of a stream of debris that comet Swift-Tuttle released into space back in the year 1479.
The Planets and the Moon
Mercury can be seen low on the western horizon just after sunset the first few days of August.
Venus is the bright morning star. Look for it before sunrise in the east. Venus and Saturn will be side by side on the morning of the August 31.
Mars, hiding in the glare of the sun, is not to be found this month.
Jupiter is setting earlier each evening of the month. Find it in the west after sunset.
Saturn is rising in the early morning this month, but later each day.
With good binoculars, Uranus may be visible in constellation Aquarius.
Neptune will reach its closest approach to Earth—a mere 2.7 billion miles away—on August 5. Try using a small telescope to find it in the constellation Capricornus.
The Moon is new on August 15, looking east at 10:00 p.m., and full on August 29.
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The LodeStar Astronomy Center and The Albuquerque Astronomical Society will cohost the third annual Astro-Images of New Mexico: Portraits from the Foothills of Space astrophotography contest and exhibition. Amateur photographers are invited to submit their celestial images for an exhibition celebrating the beauty of New Mexico's skies.
Images submitted for consideration must have been created in New Mexico. The four submission categories are: Land and Sky; Plate/Film/Digital; CCD (very light-sensitive digital imaging); and a new category this year, Photo Illustration. The contest deadline is August 31.
Up to fifty works will be selected for display at the LodeStar Astronomy Center, in the New Mexico Museum of Natural History and Science. The exhibition will hang from October 2004 through February 2005. Prizes will be awarded for Best of Show, as well as for first and second place in each of the four categories. Prizewinners will be announced at the TAAS monthly lecture on Saturday, October 2, to be held at LodeStar.
Entries must be postmarked or hand-delivered by August 31 to Karen Keese, LodeStar Astronomy Center, 1801 Mountain Road NW, Albuquerque NM 87104. Hand-carried entries may be delivered to the security desk at the Museum of Natural History and Science, 1801 Mountain Road NW. Contest rules and entry forms are available at www.lodestar.unm.edu/events.html and www.taas.org/astroimages.html. For more information, contact Karen Keese at 505-841-5972 or email@example.com.
The LodeStar Astronomy Center, located in Old Town Albuquerque, is a University of New Mexico project in partnership with the New Mexico Museum of Natural History and Science. The center includes a planetarium, motion-simulation theater, observatory, exhibit gallery, and astronomy store. For more information, call (505) 841-5955.
The Albuquerque Astronomical Society is a nonprofit organization and one of the largest amateur astronomy groups in the country. Its history dates back to the 1950s. The mission of TAAS is public astronomy outreach and education. For information, call (505) 254-TAAS.