Wednesday, February 04, 2009
The skies the limit
In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn, slightly scattering sunlight, in this exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the image. Seen in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above. Far in the distance, at the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth.
What's happened to the setting Sun? An eclipse! Two days ago, the Moon eclipsed part of the Sun as visible from parts of Africa, Australia, and Asia. In particular the above image, taken from the Mall of Asia seawall, caught a partially eclipsed Sun setting over Manila Bay in the Philippines.
Why is there methane on Mars? No one is sure. An important confirmation that methane exists in the atmosphere of Mars occurred last week, bolstering previous controversial claims made as early as 2003. The confirmation was made spectroscopically using large ground-based telescopes by finding precise colors absorbed on Mars that match those absorbed by methane on Earth. Given that methane is destroyed in the open martian air in a matter of years, the present existence of the fragile gas indicates that it is currently being released, somehow, from the surface of Mars. One prospect is that microbes living underground are creating it, or created it in the past. If true, this opens the exciting possibility that life might be present under the surface of Mars even today. Given the present data, however, it is also possible that a purely geologic process, potentially involving volcanism or rust and not involving any life forms, is the methane creator. Pictured above is an image of Mars superposed with a map of the recent methane detection.
If every picture tells a story, this one might make a novel. The six month long exposure compresses the time from December 17, 2007 to June 21, 2008 into a single point of view. Dubbed a solargraph, the remarkable image was recorded with a simple pinhole camera made from a drink can lined with a piece of photographic paper. The Clifton Suspension Bridge over the Avon River Gorge in Bristol, UK emerges from the foreground, but rising and setting each day the Sun arcs overhead, tracing a glowing path through the sky. Cloud cover causes dark gaps in the daily Sun trails. In December, the Sun trails begin lower down and are short, corresponding to a time near the northern hemisphere's winter solstice date. They grow longer and climb higher in the sky as the June 21st summer solstice approaches.
Have you ever seen the band of our Milky Way Galaxy? In a clear sky from a dark location at the right time, a faint band of light becomes visible across the sky. Soon after your eyes become dark adapted, you might spot the band for the first time. It may then become obvious. Then spectacular. One reason for a growing astonishment might be the realization that this fuzzy swath contains billions of stars and is the disk of our very own spiral galaxy. Since we are inside this disk, the band appears to encircle the Earth. Visible in the above image, high above in the night sky, the band of the Milky Way Galaxy arcs. The bright spot just below the band is the planet Jupiter. In the foreground lies the moonlit caldera of the volcano Haleakala, located on the island of Maui in Hawaii, USA. A close look near the horizon will reveal light clouds and the dark but enormous Mauna Kea volcano on the Big Island of Hawaii. If you have never seen the Milky Way band or recognized the planet Jupiter, this year may be your chance.
Tomorrow, a few lucky people may see a "ring of fire." That's a name for the central view of an annular eclipse of the Sun by the Moon. At the peak of this eclipse, the middle of the Sun will appear to be missing and the dark Moon will appear to be surrounded by the bright Sun. This will only be visible, however, from a path that crosses the southern Indian Ocean. From more populated locations, southern Africa and parts of Australia, most of the Moon will only appear to take a bite out the Sun. Remember to never look directly at the Sun even during an eclipse. An annular eclipse occurs instead of a total eclipse when the Moon is on the far part of its elliptical orbit around the Earth. The next annular eclipse of the Sun will take place in 2010 January, although a total solar eclipse will occur this July. Pictured above, a spectacular annular eclipse was photographed behind palm trees on 1992 January.