Meanwhile, earthlings have an historic chance to see Mars at its brightest, and to see the red planet at any given instant as it existed just 186 seconds earlier in time.
Start tonight
Already Mars cannot be missed. Just look low in the east-southeast sky on any clear, balmy evening soon after darkness falls and you'll see a fiery yellow-orange "star" blazing brilliantly.
Named for the Roman god of war, Mars is often called the Red Planet. But anyone who takes even a casual glance will see that it's more like a yellowish orange the color of a dry desert under a high Sun. Mars is much like a desert, in fact, dry and covered in sand-like dust. So a desert under the Sun is exactly what you're looking at, since Mars is visible because of the sunlight it reflects our way.
From now into September, Mars shines with a topaz glow that is brighter than any other object in its region of the sky, except on those nights when the Moon is in the general vicinity (such as on Aug. 12 and 13, which will be a great stretch of time to see the two travelling through the sky together).
As with any unusually close approach of Mars to the Earth, this one makes Mars appear exceptionally brilliant and indeed, from now into the early fall, Mars will easily outshine Sirius (the brightest of all stars) and even Jupiter (the planet normally second in brightness only to Venus).
Skywatchers should note, however, that to the naked eye Mars still appears as a point of light, not anything near as impressive as the Moon. Telescopes are required to glimpse views of any features on the surface of Mars.
The setup, by the numbers
On Aug. 28, Mars will reach "opposition," the moment when the Sun, Earth, and Mars form a straight line in space, with Earth and Mars on the same side of the all-important star.
When a planet reaches opposition, it lies exactly opposite the Sun in our sky: It rises at sunset, reaches its highest point in the sky at midnight, and sets at sunrise. To imagine this from above, envision the solar system as a giant racetrack. Earth is moving in the inner lane. Mars comes to opposition when the faster-moving Earth overtakes and passes the outer planet. [Animation]
Mars comes to opposition about every 26 months. But because Earth and Mars both have elliptical orbits -- not quite circular -- no two oppositions are created equal.
This year's opposition is superior to all the others in nearly 60,000 years because Mars will be very near its closest point to the Sun (perihelion) when coming to opposition. Such "perihelic oppositions" of Mars are rather infrequent, occurring about every 15 to 17 years.
Recent perihelic oppositions saw Mars approach Earth to within 35.1 million miles in September 1956, 34.9 million miles in August 1971 and 36.5 million miles in September 1988.
Because Earth and Mars follow elliptical orbits around the Sun, Mars' closest approach to Earth usually occurs several days before or after opposition. This year Mars will arrive at perihelion just a scant 42 hours after its opposition.
So on Aug. 27, according to astronomer Myles Standish at NASAs Jet Propulsion Laboratory, Mars will come within 34,646,418 miles (55,758,006 kilometers) of Earth at 5:51 a.m. EDT, which is just about as close as it can possibly come.
At that moment, it will then take a light beam 3 minutes and 6 seconds to cross the interplanetary gulf between Earth and Mars.
Things won't appear much different in the nights and mornings immediately surrounding that historic moment, so great observing can be done without worrying about the exact moment.
Opposition comes the following day, Aug. 28. The next opposition to bring Mars this close -- closer, actually -- will not occur until Aug. 29, 2287. The distance will be 34,603,170 miles (55,688,405 kilometers).
The show goes on
Even after the main event this year, Mars inevitable fade-down will initially be very slow and gradual.
In fact, it will still continue to shine at its absolute brightest magnitude of 2.9 through Sept. 2. (Astronomers use negative numbers on their scale of magnitude to denote the brightest objects.) Mars will still outshine Jupiter through Oct. 8. And it will continue to rival Sirius, the brightest of all stars, until Oct. 28.
The next opposition of Mars will come in early November of 2005, but because Mars will then be more than 8 million miles farther from Earth as compared this months extreme opposition, it will appear to shine with just two-thirds of its peak 2003 radiance.
Interestingly, there is a long-term cycle of 79 years where the circumstances of any particular Mars opposition will replicate almost exactly.
On Aug. 22, 1924, for instance, Mars made nearly as close an approach to Earth as this year. In fact, at its closest in 1924 it was just 11,764 miles (18,930 kilometers) farther from Earth than it will be this year on Aug. 27. And 79 years from now, on Aug. 30, 2082, Mars will again make another exceptionally close approach to Earth, though again falling just short of matching this years proximity, by 78,487 miles (126,300 kilometers).
Basic Sky Guides
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