A Close Pass With Mars
- Jay Ryan
- 2003 13 Aug
"The LORD by wisdom hath founded the earth; by understanding hath he established the heavens." - Prov. 3:19
Every seasoned skywatcher knows that the planets are always visible most every night as bright "stars" in the night sky. At various times, we can best see certain planets in the morning before sunrise, and at other times, we can see the planets in the evenings after sunset.
And in general, most of the brighter planets are always easy to find, and behave in a very regular manner. The planets Venus, Jupiter, and Saturn are very conspicuous wherever they are in the night sky. Venus and Jupiter are the brightest objects in the sky, after the sun and moon, and shine steadily at a near constant brightness.
But there is one notable exception: the planet commonly known as Mars. Most of the time, Mars is a faint, indistinct object, hard to find in the sky unless you know exactly where to look. But about every 26 months, Mars brightens nearly 100 times, erupting to a brightness exceeding Jupiter, far surpassing all the other fixed stars. We are currently in a season of such brightness. In fact, for reasons explained below, Mars will be brighter in August 2003 than at any other time in history.
At any brightness, Mars has a distinctly orange color. When it is at its brightest, Mars has a copper color very similar to a shiny, new penny. Modern science has shown that this is due to iron oxide chemical compounds on the surface of Mars, giving it a "rusty" color, the source of Mars's nickname "The Red Planet."
Closest Approach Ever
In classical astronomy, the "inferior planets" are Venus and Mercury, the two planets inside the Earth's orbit, closer to the sun than our world. The "superior planets" are Mars, Jupiter, Saturn and the faint outer planets. The Earth is closest to one of the superior planets at "opposition," when Earth is directly in a line between the planet and the sun. At this time, the planet is "opposite" the sun in the sky, and can be seen rising in the East just as the sun sets in the West.
At opposition, the planet is generally at its closest to the Earth, and is therefore at its brightest. But Mars is the closest of all the superior planets, and so has a very short distance to the Earth during opposition. And Mars is also a very small planet, not very bright when it is at a place in its orbit far from the Earth. Also, Mars has the greatest percentage "spread" of distances from the Earth. Mars is usually around 40 million miles from us at opposition and 235 million miles when at superior conjunction, the opposite side of the sun from Earth. For these reasons, Mars changes dramatically in brightness as it approaches opposition.
Like most of the planets, Mars has a "lopsided" elliptical orbit. Each of the planets has points in their own orbits where they are closest and farthest away from the sun. It so happens that Mars is more lopsided than all of the other classical planets except Mercury. So depending on how Mars and the Earth line up in their orbits, Mars can be brighter at some oppositions than at others.
Planets are closest to the sun at "perihelion," a Greek-derived word that means "next to the Sun." The perihelion of Mars is at a place in its orbit corresponding to "a heliocentric longitude of 336.1 degrees." Without explaining all that, let's just say that Earth passes the point of Mars' perihelion every year on about August 27. However, the planets are all constantly in motion. In any given year, when the Earth passes this point, Mars is likely to be found at some other point in its orbit - except in 2003.
This year Mars will reach opposition on Thursday, August 28, at a place very near the actual point of perihelion. So for this reason, Earth and Mars are extremely close to their theoretical minimum possible distance. As a matter of fact, it has been calculated that Mars and Earth have never been closer at any point in history.
And so, Mars will shine brighter in August 2003 than it has ever shown before. And it will appear larger in a telescope than it has ever appeared before. Of all the great astronomers of history - Ptolemy, Kopernik, Tycho, Kepler, Galileo - none of them ever saw Mars as we will be able to see it this month. And Mars will never again present itself like this in the lifetimes of even our youngest children. So Mars truly is a special sight this month, and one your family needs to get out and see.
So Just How Special Is It?
Having said all that, the fact is, Mars is only at its closest by a small percentage over other close oppositions. In general, Mars is always brighter during oppositions in the months on either side of August. And conversely, Mars is always fainter during oppositions on either side of January, when Mars is near "aphelion," its farthest distance from the Sun.
In August 2003, Mars will have a least distance of 0.37272 astronomical units, which is about 34.6 million miles from Earth. But Mars last had an August opposition on August 12, 1971. At that time, the least distance was 0.37569 AU, and Mars was 276,000 miles more distant than this year. This is only a little more than the distance from the Earth to the Moon, a gnat's whisker in astronomical terms.
This August, Mars will look its largest through a telescope. Through a scope, Mars will have an apparent diameter of 25.11 arcseconds, a new record. But this is only 0.8% larger than the 24.91 arcsecond size observed in August 1971. So technically this is the closest opposition ever. But if you are as unimpressed by negligible percentages as I am, we can at least agree that this is the best opposition of Mars in a generation.
Also, we won't do too badly with the Mars opposition of July 31, 2018, in which it will more distant than 1971 (and thus a little smaller and less bright). But the next best occurrence will be on August 15, 2050, which our kids might enjoy but we parents can expect to miss!
This current opposition will finally be surpassed on August 29, 2287, when Mars will appear to be 25.14 arcseconds in apparent size, a whopping 0.1% bigger than this year. At this time, Mars will be a trivial 43,710 miles closer to the Earth than it will be this month. I've been driving my 1988 Ford Crown Victory since it was new and it had about that many miles on it in 1990!
Seeing Mars in August 2003
On any clear night this month, Mars can be seen rising in the southeast a couple hours after sunset. You can't miss Mars, since it is a fiery copper-colored "star," greatly outshining any other star currently in the evening sky. Our Southern Hemisphere readers should see Mars at a reasonable evening hour.
But since it is summer for our Northern Hemisphere readers, the sun sets late, and Mars won't be very high in the sky until about midnight. This will be quite a bit after the bedtimes of our younger scholars. However, as Mars approaches opposition, it will rise earlier and earlier over the course of the month, and the northern days will grow shorter.
Mars and the Earth will actually have their closest approach on Wednesday, August 27. Since the Earth's orbit is also a bit lopsided, the two bodies are technically at their closest the day before opposition. But on Thursday, August 28, Mars will finally be at opposition. In the weeks and months thereafter, Mars will be visible in the evening sky after sunset. So we'll be spending some time with Mars in coming months, and we'll tell you about upcoming conjunctions of the Moon with Mars.
Telescope Viewings of Mars
The "disc" of the planet Mars will only be visible under the magnification of a telescope. With an apparent angular size of 25.11 arcseconds, Mars will have a visible diameter of only 1% that of the full Moon. To put this in perspective, look at a dime with the words "In God We Trust." If you took a dime and held it arm's length, ten Mars would fit side-by-side across the "O" in "God!"
Whatever you do, please don't run out and buy a telescope just to see Mars. Even at it's best, Mars always looks tiny in a small family telescope, about half the diameter of Jupiter. Mars would typically look like a little orange ball. If you have a fancy scope and a pristine sky, you might see the white polar cap on Mars, and maybe some of the dark green surface markings. But you can expect these features to be indistinct at best.
Your best bet is to visit a planetarium or astronomy club in your area. Since Mars is being hyped in the media this month, the planetariums are all doing special shows about Mars. Also, most communities have a local amateur astronomy club, many of which work with a planetarium. The amateur clubs always host public telescope nights, and this would be a great time to see Mars through a club member's telescope. The folks at the clubs and the planetariums are always trying to drum up attendance for their events, and would be glad to see your family or homeschool group. Check out the resources page at http://skyandtelescope.com for a list of clubs, planetariums and observatories in your area.
'Til next time, God bless and clear skies!
Be sure to visit The SkyWise Archive, a collection of educational astronomy cartoons to help your family learn about the sky. Check it out at http://www.mangobay.cc/users/moonfinder. Jay Ryan is the creator of "The Classical Astronomy Update," a free e-mail newsletter for helping Christian homeschool families learn more about what's up in the starry sky. If you would like to receive the Update, please drop Jay an e-mail at [email protected].