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AURORA OUTLOOK: Geomagnetic activity is low now, but it will likely increase on Dec. 21st when Earth runs into a solar wind stream flowing from a coronal hole on the sun. First contact with the stream could spark auroras at high latitudes.
DUST STORM ON MARS: With three space probes set to land on Mars in the weeks ahead, mission controllers are monitoring an ongoing martian dust storm. The movie below, which shows how the dust has spread since the storm began last week, comes from NASA's Mars Global Surveyor spacecraft in orbit around Mars:
In recent days, the dust clouds have grown large enough for amateur astronomers to see through backyard telescopes.See e.g. these images of Mars on Dec 13th, 14th and 16th from Don Parker; Dec. 15th and 18th from Ed Grafton; and Dec. 16th and 19th from Joel Warren.
A curious side-effect of the storm is the increasing brightness of Mars. "Mars was about 0.17 magnitudes brighter on Dec. 15th," says ALPO executive director Richard Schmude, Jr. "This increase is due to [sunlight reflected by] dust." For comparison, a global dust storm in 2001 caused Mars to brighten by 0.25 magnitudes.
DIAMOND DUST: Ordinarily, rainbow-colored sundogs appear high in the sky among the icy clouds that create them. But in some places, like Alaska, they can materialize right in front of you. Here's an example, photographed by Lesa Hollen of Fairbanks, Alaska, on Dec. 16th:
"The rainbow colors were brilliant and had a mystical effect with the Northface of the Alaskan Range silhouetted in the background," she says.
Sundogs like this are caused by diamond dust. Atmospheric optics expert Les Cowley explains: "When it is very cold (air temperature below freezing) large ice crystals, called diamond dust, can sometimes float nearby in the air. The halos they form appear to be in front of distant hills or trees. They also sparkle as the individual ice crystals glint in the sun."