Mars’s Dazzling Sky Show

Because it is close to Earth in space, Mars looks like a dramatically bright 'star' in the sky. Mars is well up in the southeast by about 9 p.m. during early September. It gets a little higher in the sky and shifts toward the south during the night.
Sky & Telescope illustration by Steven Simpson.
Now that Mars's record-breaking close approach is history (it happened on the night of August 26–27) is the show over?

No way!

Mars remains just as big and bright, for all practical purposes, during at least the first half of September. It will shrink and fade only a little until well into autumn. Moreover, in one way the show is getting better than ever! Every day Mars rises higher in the sky earlier in the night, which makes it easier to view at a more convenient hour.

Mars is the breathtakingly bright "star" in the southeast after dark. You can't miss it. Mars shines many times brighter than any actual star in the sky. Anyone can see it, no matter how little you know about the stars or how badly light-polluted your sky may be. It gets higher as the evening grows late, and by midnight or so, it's at its very highest in the south. The planet displays a clear, fiery yellow or yellow-orange hue, due to rust-like iron compounds in its surface.

Mars at 4:30 Universal Time on August 26. The South Polar Cap is at top, the dark spot right of center is Solis Lacus, and the dark mass from the center to the left includes Mare Erythraeum, Aurorae Sinus, and Margaritifer Sinus.
Image by Dennis di Cicco.
Even when it's so near, however, Mars is challenging to study in a telescope. At moderately high magnification it appears as a small, bright ball displaying subtle dark markings, a bright white South Polar Cap (now shrinking in the warmth of the Martian late spring), and perhaps traces of bluish white clouds rimming some of the planet's edges.

The brightest yellow areas are deserts covered by fine, windblown dust. The darker markings are terrain displaying more areas of bare rock (much of it ancient lava flows) or darker dust. Mars rotates every 24½ hours, so you can see it turning in just an hour or two of watching.

The dark circular feature near the center of this video frame from August 25, 2003, is Solis Lacus, sometimes called the Eye of Mars. Click on the image to see the 1.1-megabyte QuickTime movie from which this frame was taken(requires QuickTime Player or another MOV-compatible media player).
Courtesy Johnny Horne.
To see much detail on Mars, you’ll need at least a moderately large telescope with high-quality optics. (For the lowdown on how to select a telescope wisely, see "Choosing Your First Telescope".) You'll also need to wait until Mars rises high in the sky, well above the thick, murky layers of atmosphere that hug the horizon. And the "seeing" must be good — that is, the tiny heat waves that constantly ripple through the Earth's atmosphere should be minimal. These waves cause highly magnified telescopic images to constantly shimmer and fuzz. The quality of the seeing changes greatly from night to night and sometimes from minute to minute.

There has been some confusion over exactly how much of a record Mars set on August 27th. Sky & Telescope senior editor Roger Sinnott got to the bottom of the matter months ago, finding 57,617 BC to be the correct date when Mars last came this near to Earth.

The orbits of the Earth (blue) and Mars (red) around the Sun. Mars moves in a noncircular orbit, and it was closest to the Sun almost precisely when Earth moved past it on August 27th. On that date at 5:51 a.m. Eastern Daylight Time, the two planets were only 34.6 million miles apart — their closest pairing in nearly 60,000 years. The Sun and planet disks are not shown to scale.
S&T illustration by Steven Simpson.
That was 59,619 years ago (taking into account that there was no "year zero" between 1 BC and AD 1). For the full story, see "A Mars Record for the Ages". We won’t have to wait as long for this year's record to be broken: Mars will come just a hair closer on August 28, 2287.

Mars was nearly this close in 1988, and for all practical purposes it looked much the same as now. That year it reached an apparent diameter of 23.8 arcseconds as seen in a telescope; this year it topped out at 25.1 arcseconds wide (the angular size of a penny seen at a distance of 500 feet). And Mars will make another good pass by Earth as soon as October 2005, appearing 20.2 arcseconds wide.

Read more about Mars is in the June, July, and August issues of Sky & Telescope and online in "Mars at Its All-Time Finest".

COMMENT