Mars meets anti-Mars
Right: Duane Hilton's rendering of Mars, Antares, and the crescent Moon above an old barn just after sunset on Sept. 15, 1999, two days before closest approach. While you're enjoying the view of Mars and Antares in the southwest, don't forget to look slightly eastward to view the Galactic Center in Sagittarius. How to find Mars, Antares, and the galactic center.
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This week Mars will appear to be about twice as bright as Antares. Like all planets, Mars shines by reflected sunlight and is intrinsically dimmer than a star. Mars seems to be brighter because it is much closer than Antares. The distance from Mars to Earth is a mere 191 million km -- just a hop, skip, and a jump by cosmic standards -- while Antares lies 30 million times further away (6x1015 km).
Antares is 700 times larger, 9000 times more luminous and about 15 times more massive than the Sun. Although it's big and bright, most of Antares is really fluffy and insubstantial. The star's density is a million times less than water. In fact, the outer layers of Antares are so thin that you could fly a spaceship through them and barely notice the difference.
Above: This picture shows what the sky just around Antares looks like in a long photographic exposure obtained with a large telescope. Why is the sky near Antares and Rho Ophiuchi so colorful? [Click here to find out.]
The close approach of Mars and Antares is 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
The Planet Mars - from the SEDS Nine Planets web site
Mars Global Surveyor - home page
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 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 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 Science News
A close encounter with the Red Planet -- Mars makes its closest approach to Earth in 1999. Apr 23, 1999 NASA Science News
Summer snow on Mars -- New Mars Global Surveyor images reveal snowy slopes. Mar. 25, 1999 NASA Science News
A new face on Mars has scientists smiling -- MGS beams back pictures of the "Happy Face Crater". Mar. 12, 1999 NASA Space Science News
Mars mapping begins in earnest -- MGS achieves its final orbit. Mar. 12, 1999 NASA Science News
A steamy cover-up on the red planet -- New evidence for active volcanism on Mars. Feb. 18, 1999 NASA Science News
The Sands of Mars -- Oct. 29, 1998 NASA Science News
More NASA Science News
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|Author: Dr. Tony Phillips
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