MARS IS HERE!
Dr. Terry Goforth
Associate Professor of Physics, SWOSU
August 2003

This month offers sky watchers the chance of a lifetime, or more appropriately, the chance of many, many lifetimes. On August 27, 2003, at 4:51 AM CDT, Mars will pass a mere 34,646,418 miles from Earth. While this may not seem all that close, it is notable that Mars hasn't been that near to Earth since 57,517 BC! Fortunately for Mars lovers, it won't be another 60,000 years until this happens again. Mars will come this close again 283 years from now on August 28, 2287.

Does this mean there's going to be some kind of spectacular show in the sky? Well, yes and no. Yes, because Mars will appear noticeably brighter and larger than normal. No, because while this is the closest approach in nearly 60,000 years, Mars has been almost this close as recently as 1988 and in fact is nearly this close every 15 to 17 years.

So why look? This month Mars is outshone in the night sky only by the moon. Venus would be brighter if it were up, but Venus doesn't rise until dawn. Even Jupiter, normally the second brightest of the planets never gets as bright as Mars is now. Except for the moon, Mars will dominate. To make things better, August 27 is also the date of the New Moon, so for about a week before and after that Mars will be the main attraction.

Mars will also look larger than usual. To the naked eye, this size difference will be unnoticed, but astronomers, both professional and amateur, will be turning their telescopes of all sized toward the Red Planet for a look. Since Mars will be closer and larger than normal, telescopes will reveal more detail than is usually observed.

Mars's apparent size increases until August 27, then decreases
This image shows the relative size of Mars as seen from Earth through the last half of 2003.  NOTE:  Mars will not look this big in the sky and you will not see the detail shown here.  (Image of Mars from NASA.)

Where and when should you look? Through August and September, Mars rises in the east-southeast, rises about halfway up in the southern sky, and then sets in the west-southwest. Around August 20, Mars is rising around 9:00 PM and reaching its highest point in the southern sky around 1:30 AM. By the end of August, it will rise around 8:30 PM and reach maximum height around 1 AM. These times will continue to shift earlier by about one-half hour every week. Although the closest approach is in the wee morning hours of August 27, Mars will look fairly spectacular anytime from now to mid or late September, so you can choose your night (weather permitting). Don't expect to get a good view of Mars until at least an hour or so after it rises, so this is a late-night activity. Early risers can take a look in the west an hour or more before sunrise.

What equipment do you need? Really, all you need are your eyes and a dark sky in the south. Mars appears orange or red depending on the viewer's definition of the color and the amount of dust and pollutants in the sky. A few stars appear the same color, but they won't be nearly as bright. (Mars is unmistakable-it's the bright orange "beacon" in the sky.) Also, stars twinkle, planets (including Mars) don't. If you have binoculars, you can actually see the disk of the planet. It's best to mount them on a steady platform if you can. Small telescopes will also provide a good view. (Of course, if you have a big telescope, go for it!)

Mars is closest to Earth during opposition. Why is Mars so close? Mars is going through what astronomers call a "perihelic opposition." This involves both the shape of Mars's orbit and the relative positions of Mars, Earth, and the Sun.

Opposition occurs when Mars is more or less directly opposite the Sun as seen from Earth. This happens about once every two years. Both Earth and Mars are orbiting the Sun, but Earth has the "inside lane," so we "lap" Mars every 25.5 months. Each time we pass by Mars, Mars goes through an opposition. It is at these times that Mars is fairly close to Earth. Generally somewhere between 34.6 and 63 million miles separates them at each opposition.

The separation between Mars and Earth at opposition is not always the same because Mars's orbit is not exactly circular. It is elliptical or oval, as are all planetary orbits, and the Sun is not exactly in the center. The point in Mars's orbit where it is closest to the Sun is called the perihelion, (peri for close, as in periscope, and helion from helios, Greek for the sun). This of course happens once each time Mars completes an orbit (about 23 months).

A perihelic opposition occurs when these two events happen very close to each other. This month, Mars goes through opposition on August 28 and passes through perihelion on August 30. The Earth, traveling on the inside orbit, is passing Mars and makes its closest approach on August 27. Since Mars is at its closest to the Sun and Earth is inside Mars's orbit, Mars and Earth are closer to each other than at almost any other time. Perihelic oppositions occur about every 15 to 17 years. The exact timing of Mars's opposition, when it passes through perihelion, and when Earth makes its closest approach to Mars determines the minimum separation between the two planets. This year, the timing of these three events has converged to bring Earth somewhat closer to Mars than in the "typical" perihelic opposition.

Why all the fuss? Perihelic oppositions offer astronomers the best possible Earth-based view of Mars. With telescopes of sufficient size, surface details can be observed with better clarity than at any other time. Also, this is an opportune time for space agencies to launch probes to Mars. They have to cover less distance, which means less travel time and less fuel expended. The European Space Agency's Mars Express launched in June and will arrive at Mars in December. NASA's Mars Exploration Rover Mission launched two rovers, Spirit and Opportunity in June and July. They will arrive in January of next year.

More information: There are many web sites and publications with information on this event. Try the the June 2003 issue of Sky & Telescope (skyandtelescope.com), the August 2003 issue of Astronomy magazine (www.astronomy.com) or the July/August 2003 issue of Mercury magazine (www.astrosociety.org/pubs/mercury/mercury.html). NASA has articles at www.jpl.nasa.gov/solar_system/features/mars-opposition.cfm or science.nasa.gov/headlines/y2003/18jun_approachingmars.htm.

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Last update:  August 19, 2003