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Astronomical Observatory: Cool Images

Images: Mars, August 17, 2003

Contents: What is special about the 2003 opposition? On August 27, Mars is in opposition: that is to say, directly opposite the Sun as viewed from Earth. A planet in opposition is as close to Earth as it can be, and is visible all night long. Mars reaches opposition every 26 months, but the 2003 opposition is special. Since Mars is also at the nearest point of its elliptical orbit, it is substantially closer to Earth than at a typical opposition. It will shine at -2.9 magnitude, brighter than Jupiter at its brightest, and fully 72 times (4.7 magnitudes) brighter than Mars at its faintest. It is 20% closer than the next opposition in October 2005.

What do we see? In our August 17 image, Mars is within 2% of the size it will have at closest approach. The visible hemisphere is almost completely illuminated by sunlight. A small sliver of the right rim of the planet is in darkness. Due to the thinness of the atmosphere (1% that of Earth) and the lack of water vapor, the markings we see all arise from the solid surface.

The dominant coloration is reddish, due to iron contained in the dust that swirls around the planet. Portions of the southern (lower) hemisphere are darker where rock is exposed. The south polar cap, where it is now summer, is clearly visible at the bottom of the frame. This is largely composed of water ice. In the winter the ice cap swells in size as carbon dioxide from the atmosphere freezes (dry ice). (A complete cycle of seasons on Mars takes 23 months.)

What do we not see? Mars also has two tiny moons, Phobos and Deimos. They are so small, however, that they can only be seen in a long exposure image, one in which the planet itself would be saturated.

The image is centered on Martian longitude 167 degrees. Although it is just beyond the resolution of our image, Olympus Mons, the largest volcano in the solar system is near the upper-right edge of the planet, and the three Tharsis volcanoes are near the center-right edge.

Processing: This full color image was made from a series of images taken by Larry Molnar on 17 August between 2:45 and 3 am EDT. Dozens of exposures were made through red, green, and blue exposures. However, even though the exposure times were short (0.1s for red and green, 0.2s for blue), and an aperture mask was used to reduce the effective diameter of the mirror, most images were blurred by atmospheric fluctuations. Andrew Vanden Heuvel, a student, combined the best 2 red, 3 green, and 1 blue images to make the final product. Unsharp masking was applied to each color to enhance the resolution.

Orientation and scale: North is up and East is to the left. The planet has a diameter of 25 arcseconds. Mars was in the constellation Aquarius, at celestial coordinates 22h48m21s, -14deg49' (epoch 2000).

Content updated 8/20/03


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