SJAA Ephemeris November 2005 | SJAA Home | Contents | Previous | Next

The Shallow Sky

All Mars, All The Time

Akkana Peck


This month the show is all Mars, all the time.

The red planet reaches opposition on the evening of the 7th, right around midnight. The planet is already past its closest approach, which happened on October 29th, but it will remain large, bright, and high in the sky all month and into next month.

Mars' southern pole is tipped toward us. But it's not a radical tilt like the last few oppositions, merely ten degrees; you'll probably be able to see most of the northern features fairly well, as well as the southern ones. You may even be able to see both polar caps at once.

That is, you might be able to see some of the dry-ice haze of carbon dioxide vapor making up the North Polar Hood, plus the very small south polar cap. It's late summer there, so the cap is as small as it gets. It's also considerably offset from the pole; depending on how Mars is rotated, the cap may be invisible, or it might be fairly easy. It should be fun to watch it over a period of a couple of weeks (or over the course of a single long evening) as it appears to wax and wane.

Why one evening versus a couple of weeks?

Mars' day is slightly longer than Earth's. That means that if you go out to observe Mars at 10pm tonight, tomorrow night at 10pm you'll be looking at a point slightly earlier in the Martian day from the view you saw tonight. It takes a bit over a month for the cycle to complete and bring you back to the place where you started. If you don't like the side of Mars you're seeing right now, wait two weeks and you'll be looking at the opposite side of the planet.

Of course, if you're in a hurry to see a different side of the planet, you don't have to wait a month. Just keep watching over a period of hours, and you'll see new features rotate into view.

As November opens, evening viewers will see dark Syrtis Major, centered on the planet, extending northward from the bright circular impact basin Hellas. These are the two Martian features which are easiest to spot, so if you haven't looked yet, it's the perfect time to grab a telescope and get started.

Over the next week, Mars rotates so that the three linear dark areas Maria Tyrrhenum, Cimmerium, and Sirenum will be visible. The latter two join together to make a long diagonal slash across the southern hemisphere, separated from Tyrrhenum by a much lighter area. They're a little more subtle than Syrtis Major and Hellas, but it's also a great area to see and sketch lots of interesting detail.

By mid-November, Tyrrhenum and Cimmerium will be mostly gone, but Sirenum will dominate the south. The north appears initially as a featureless expanse of orange: this is a region known as Amazonis, and to its east (rotating in a later in the week) are Olympus Mons, the highest volcano in the solar system, and the Tharsis Plateau, home to three other huge volcanoes. You can't see the volcanoes directly. But look for lighter areas which change from day to day - orographic clouds over the volcanoes.

By the 22nd, Lacus Solis comes into view. It's a fairly small dark spot by itself, but from the right angle, the dark areas nearby frame it to become the pupil of a human eye - the "eye of Mars".

To the north, Vallis Marineris is more or less centered - a very tough target for advanced observers. Most of the time you won't see anything, but several SJAA members have suspected they say parts of the enormous canyon as a thin line when the atmosphere on our end was rock steady. On the northeast limb, look for the edge of dark Acidalia.

Finally, by the end of the month, dark Margaritifer (aren't Mars names great?) is showing well, with all the interesting splotchy bays at its north end. South of it is lighter Mare Erythraeum, and even farther south, not quite to the pole, bright Argyre is another impact basin like Hellas but smaller.

On the eastern limb, you can see the grasping finger of Sinus Meridiani peeking over the limb. Over the first week in December you can watch that rotate in, followed by Syrtis Major, which starts the cycle all over again in December.

It's a good thing there's so much to look at on Mars, because there's not much other planet action in the sky.

Venus continues the stunning display it's been showing us since late September. Since it's quite far south, it rides fairly low in the western sky at sundown, but you still get another couple of hours to view it before it sets, and by month's end it shows a slight crescent.

Uranus and Neptune are still in the evening sky, but they're getting lower. Catch them early in the evening if you want a good look. Saturn rises before midnight, but doesn't get high in the sky until the wee hours of the morning. Jupiter rises just before dawn. Mercury is too close to the sun to be easily observed from San Jose, though observers in the southern hemisphere are getting a good look.


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