This month, Mars makes its big move on Earth, but there is no need to worry: What we are about to face is not an invasion from
Mars but an invasion by
Mars. On August 27 the Red Planet will approach to 34,649,589 miles, closer than it has been at any time in recorded history. Mars will attain a magnitude of -2.9, far outshining everything else in the night sky. Finding it will be easy. Just glance up a couple of hours after sunset on a clear evening and let the dazzling, non-twinkling "star" low in the southeast grab your attention.
|A Martian crater, photographed by NASA's Mars Global Surveyor, displays a remarkable vista of sinuous gullies, possibly carved by moving water. |
Photograph courtesy of NASA/JPL/MSSS.
Never again in your lifetime will Mars be so spectacular. Planetarium computer programs such as Starry Night make it a snap to figure out when Mars will next pay such a close call: August 28, 2287. Ascertaining the last time Mars came this near is more challenging. The gravitational interplay of the planets constantly alters the shapes of Earth's and Mars's orbits, from rounder to more oval and back again. As a result, the narrowest gap between the two worlds continually mutates. Orbital calculations get ever fuzzier the farther back in time you go. We do know it has been at least 5,000 years, and probably more like 60,000 years, since Mars cozied up this close to us.
Strictly speaking, Earth is the one doing the cozying. Our planet, circling the sun at 18.3 miles per second, overtakes Mars, which lopes along at 16.4 miles per second in its orbit. As Earth approaches, Mars appears to stop its normal west-to-east motion across the sky and to temporarily track east to west (known as retrograde motion) among the dim stars of Aquarius. At the beginning of the month, the planet will rise at 10 p.m. and reach its pinnacle at about 3 a.m. By the end of August, the planet will rise at nightfall and reach its highest point at 12:30 a.m. The planet will also grow steadily bigger and brighter as it migrates to more convenient viewing hours.
At its peak, Mars will appear 25.11 arc seconds wide in the August sky. At a modest 75-power magnification, the planet will look as large as the full moon does to the naked eye. All the same, backyard telescope owners may be slightly disappointed by what they see. The real Mars is yellow orange, not red, and its dusky surface features do not have the dramatic contrast of the color-enhanced images NASA distributes. Observers will need a sharp eye to see the subtle markings that pop into focus during the moments when Earth's atmosphere steadies. During those seconds of clarity, look for the white south polar cap, tiny now because the southern Martian summer is about to begin.
|Use a pair of binoculars to look just above Mars for a faint but vividly green "star": That is Uranus. The solar system's two most colorful planets float near each other for several weeks, coming closest in late September, when Mars will shine 1,500 times brighter than distant, dim Uranus.|
The Mars Odyssey
spacecraft, orbiting the planet since 2001, recently revealed that the southern cap consists mostly of water ice, not frozen carbon dioxide as astronomers had believed for decades. That discovery enhances the odds that life once took hold in or under the rusty sands of Mars, although the total amount of water we have detected there is minuscule compared with Earth's oceans.
Expect more Mars news soon. The European Space Agency's Mars Express,
along with two NASA rovers, should be en route to the Red Planet right now. If you want a good look at Mars for yourself, however, you must act quickly. Earth speeds 5 million miles closer to the planet during August but pulls away just as quickly in September. As a result, Mars nearly doubles in brilliance between August 1 and 27, then loses all that extra light during September. Likewise, the planet's apparent size grows and shrinks rapidly. The smaller Mars gets, the more magnification you'll need to scrutinize its surface.
Fortunately, Mars stays adequately large this month and the next. That will give you plenty of time to badger any friends who have large telescopes.
Learn exactly where to look for Mars over the next couple of months, and find out more about the various probes and landers that are heading toward the Red Planet right now: www.spaceweather.com/delights/mars2003_Invade.html
It's tangential to this month's Sky Lights, but wouldn't you like to know about Martian calendars? See Martian Time: pweb.jps.net/~tgangale/mars/index_new.htm
Read a Caltech press release about the recent discovery that the southern Martian ice cap is made of water ice, not frozen carbon dioxide, as had been suspected: pr.caltech.edu/media/Press_Releases/PR12342.html