The Great Dark Spot

The Great Dark Spot (GDS-89 [cite journal
last=Hammel | first=H. B.
coauthors=Lockwood, G. W.; Mills, J. R.; Barnet, C. D.
title=Hubble Space Telescope Imaging of Neptune's Cloud Structure in 1994
journal=Science | year=1995 | volume=268
issue=5218 | pages=1740–1742
doi=10.1126/science.268.5218.1740
accessdate=2008-02-27
pmid=17834994 ] ) was a dark spot on Neptune similar in appearance to Jupiter's Great Red Spot. It was detected in 1989 by NASA's "Voyager 2" probe. Although it appeared similar to Jupiter's spot, which is an anticyclonic storm, it is believed that the Great Dark Spot was a relatively cloud-free region.

Characteristics

The spot was relatively the same size as Earth itself, and was very similar in appearance to Jupiter's Great Red Spot. At first it was thought to be a storm, like the Great Red Spot, but closer observation revealed it to be a dark, elliptically-shaped depression in Neptune. Around the Great Dark Spot, winds were measured blowing up to 2,400 kilometers (1,500 miles) an hour, the fastest in our Solar System. The Great Dark Spot is thought to be a hole in the methane cloud deck of Neptune, similar to the holes in the ozone layer on Earth. In many images of Neptune, the spot has been observed at different sizes and shapes.

The Great Dark Spot generated large white clouds similar to high-altitude cirrus clouds found on Earth. Unlike cirrus clouds, however, which are composed of crystals of ice, Neptune's cirrus clouds are made up of crystals of frozen methane. And while cirrus clouds usually form and then dissolve within a period of a few hours, the clouds in the Great Dark Spot had not dissolved after 36 hours, or two rotations of the planet.

Disappearance

When the spot was to be photographed again in 1994 by the Hubble Space Telescope, the spot had disappeared completely, leaving astronomers to believe that it had either been covered up or vanished. However, an almost identical spot emerged in Neptune's northern hemisphere. This new spot, called the Northern Great Dark Spot (NGDS), has remained visible for several years. [ [http://www.solarviews.com/eng/neptune.htm Neptune ] ]

ee also

*Extraterrestrial cyclone
*Oval BA
*Small Dark Spot
*Dragon Storm (astronomy)

External links

*http://www.solarviews.com/eng/neptune.htm
*http://www.windows.ucar.edu/tour/link=/neptune/atmosphere/N_clouds_GDS.html
*http://apod.nasa.gov/apod/ap960508.html
*http://intranet.dalton.org/departments/science/Astro/planets/Neptune/the%20dark%20spot.htm
*http://www.arcadiastreet.com/cgvistas/neptune_006.htm
*http://adsabs.harvard.edu/abs/2000hst..prop.5096S

References