Mars & Spica
Right: Duane Hilton's rendering of Mars and Spica above Cape Royal just after sunset on June 8, 1999. While you're enjoying the view of Mars and Spica in the south, don't forget to look to the west at brilliant Venus which reaches its greatest apparent distance from the sun (48o) later this month.
The pair can be seen from both hemispheres as soon as the sky begins to get dark. Simply go outside and look to the south-southwest. Mars appears high in the sky from mid-northern latitudes as a fiery-reddish 1st-magnitude object about 40 degrees above the horizon. Just below Mars is Spica, a 1st magnitude blue-white giant about 220 light years from Earth. It is the 14th brightest star in the sky. Normally, Spica's blueish color is difficult to discern -- it looks white like most other stars. But this week is different. Spica's close proximity to reddish Mars makes its subtle hue stand out. Together, Mars and Spica form a truly vivid red-blue combination.
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Although Mars, which shines by relected sunlight, is intrinsically dimmer than a brilliant star like Spica, the planet is much brighter in the night sky. That's simply because it is the closer of the two. The distance from Mars to Earth is a mere 103 million km -- just a hop, skip, and a jump by cosmic standards -- while Spica lies 91,000 times further away (2x1015 km). Mars reached maximum brightness last month when it passed close by Earth and reached magnitude -1.6. As Mars and Earth continue to separate, Mars will grow dimmer and dimmer until it is only +0.4th magnitude by the end of the year.
The close approach of Mars to Spica is also a great opportunity to observe a phenomenon that is well-known to avid stargazers: Stars twinkle but planets do not (at least, not much).
Neither stars nor planets twinkle as seen from outer space, but the view from Earth's surface is a different matter. Tiny irregularities in the density and temperature of the air above us drift in front of stars and planets as we view them through the atmosphere. When a beam of starlight travels through the atmosphere, these irregularities disturb the beam making it dance back and forth slightly. That's what causes stars to "twinkle." (In scientific terms: tiny inhomogeneities in the atmospheric index of refraction cause point sources like stars to "scintillate.") Stars are so far away that they look like unresolved points of light even in large telescopes. Planets, on the other hand, are relatively nearby. They look like disks even in small telescopes. Planets don't twinkle because the scintillation of light from one side of the disk mixes with scintillation from other parts of the disk, and the disturbances cancel out. The light from planets arrives as a steady stream, not a babbling brook. It's all because planets appear much, much bigger than stars as seen from Earth.
This week's sky at a glance -- from Sky & Telescope
Mars & Spica in 1998 -- from EarthSky.com
Spica -- facts and figures from the University of Wisconsin
The Planet Mars - from the SEDS Nine Planets web site
Life on Mars - A review of evidence of signs of life in the Allen Hills meteorite
Mars Global Surveyor - home page
Mars - by Percival Lowell, 1895
Related Stories:
Search for life on Mars will start in Siberia -- Russian and NASA scientists will look for life forms in the inhospitable realm of Siberian permafrost. May 27, 1999 NASA NASA Science News
Stormy weather on Mars -- During the recent close approach of Mars to Earth, NASA's Hubble Space Telescope spotted a gigantic storm swirling near the Red Planet's north pole. May 19, 1999 NASA NASA Science News
Mars unveils a magnetic personality -- Plate tectonics on the Red Planet might have important consequences for ancient Martian life. Apr 30, 1999 NASA NASA Science News
Plate tectonics on Mars? -- Magnetic stripes on the surface of Mars are similar to fields in the sea floors of Earth. Apr 29, 1999 NASA NASA Science News
A close encounter with the Red Planet -- Mars makes its closest approach to Earth in 1999. Apr 23, 1999 NASA NASA Science News
Summer snow on Mars -- New Mars Global Surveyor images reveal snowy slopes. Mar. 25, 1999 NASA NASA Science News
A new face on Mars has scientists smiling -- MGS beams back pictures of the "Happy Face Crater". Mar. 12, 1999 NASA NASA Science News
Mars mapping begins in earnest -- MGS achieves its final orbit. Mar. 12, 1999 NASA NASA Science News
A steamy cover-up on the red planet -- New evidence for active volcanism on Mars. Feb. 18, 1999 NASA NASA Science News
The Sands of Mars -- Oct. 29, 1998 NASA NASA Science News
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| For more information, please contact: Dr. John M. Horack , Director of Science Communications |
Author: Dr. Tony Phillips Curator: Bryan Walls NASA Official: John M. Horack |
