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Now is the Time to Observe Mars
Now is the Time to Observe Mars

"Say, what's that bright orange star in the southeast late at night?"

My wife asked me this the other day. I knew right away that she was talking about Mars, since, once it's above the horizon, it's about the brightest, most easily seen object in the sky. Only the Moon, Venus, Jupiter and the star Sirius are brighter.

 


Mars rising above the northeastern horizon on the night of closest approach (October 29th) as seen at 10PM ET from mid-northern latitudes.

 

Finding Mars
Where you will find Mars in the sky depends on your location, the current date and the time of night you're looking. But there's an easy, accurate way of finding the Red Planet: use a program like Starry NightŪ. It is as simple as telling Starry NightŪ your observing location. It will show the sky for the present time and date. If you won't be observing until later, change the time accordingly. Click on the "Find" tab and look down the list of solar system objects for Mars. Click on the check box to the left of "Mars" to turn on its label, and then click on the arrow button to the far left of "Mars" and select "Centre" from the popup menu that appears. Starry NightŪ will then show you the present position of Mars, assuming it's above the horizon. Mars is far brighter than anything that's likely to be close to it except the Moon, so it should be easy to spot, even in a light-polluted city sky.

Mars takes a little more than twice as long as the Earth to make one orbit around the Sun — both planets come close to each other once every 26 months.

Mars was about as close as it can be on August 2003 — about 34.6 million miles (55.7 million km). When we catch up again in late October and early November this year, we won't be quite as close — 43.6 million miles (70.2 million km) on October 29th.

Is this bad news for Mars observers? Not really: in August 2003, Mars was located in Aquarius, really low in the sky for northern observers. This year it will be located in Aries, much higher, and above most of the atmospheric turbulence. So, even though Mars is farther away, and hence smaller in size, it should actually be easier to see more detail this year than in 2003 because of steadier images.

 


The Earth and Mars are at their closest this year on October 29th.

 

What to Look For
Like Earth, Mars is tilted relative to its orbital plane, and so it has seasons. Its pole however, points in a different direction than the Earth, so the seasons on Mars are one season "out of phase" from those on Earth. In August 2003, late summer on Earth's northern hemisphere corresponded to late autumn on Mars' northern hemisphere. In October and November 2005 it will be autumn on Earth's northern hemisphere, and so it will be winter on Mars' northern hemisphere (and also summer on Mars' southern hemisphere).

If you observed Mars through a telescope in 2003, you probably remember seeing its bright southern polar cap. Because it's now later in the Martian year, the southern polar cap will have melted away to a tiny button, very difficult to see in even the largest telescope, even though it's tilted towards us. The northern polar cap, in Martian midwinter, will be tilted away from us, and probably lost in the haze that envelops the Martian polar regions during winter. The result this year will be a Mars almost without polar caps.

The many space voyages to Mars have shown us that it is a planet of spectacular topography, from the heights of Olympus Mons, the tallest shield volcano in the solar system, to the depths of the Valles Marineris, a chasm which dwarfs the Grand Canyon. However, seen from the Earth, these features vanish because, like our view of the full Moon, the lighting comes from directly overhead, so there are no defining shadows. What we do see is a pattern of light and dark, a mosaic of darker bare highlands and lighter sand-covered lowlands. Most of these darker regions are concentrated on Mars' southern hemisphere, so they will be well presented during this apparition of Mars.

The most prominent dark marking on Mars is Syrtis Major, located at Martian longitude 290°. It is usually seen as a triangular wedge shape, sometimes with a curved tip. Between it and the south pole is a large bright area called Hellas. Extending westward from Syrtis Major is a narrow dark band, Sabaeus Sinus, ending in a forked blob, Meridiani Sinus, so named because it defines the zero meridian in the Martian longitude system. This is the area that the Mars Rover Opportunity is currently exploring. Further west, at longitude 100°, is Solis Lacus, sometimes called "the eye of Mars" because of its resemblance to a gigantic eye. West of this is what Mars observers often call "the boring side of Mars" because of its lack of dark markings. Studies of Mars from orbiting space probes reveal otherwise, since this vast plain is the location of Mars' gigantic shield volcanoes. The dark markings begin again at around longitude 180° with the broad streak of the Mare Sirenum. This lies south of the crater Gusev, where the second Mars Rover, Spirit, is on the ground exploring. Mare Sirenum extends westward into Mare Cimmerium (longitude 230°) and then Syrtis Major comes into view again.

 


Mars map showing typical features that can be seen with amateur telescopes. Courtesy of Tim Wilson.

 

Observing Tips
Mars looks so big and bright to the naked eye, that the view through an amateur telescope might disappoint at first. Jupiter has its belts and moons, Saturn has its rings, but Mars looks like nothing more than a tiny orange dot at first glance. There are several secrets to getting Mars to reveal its sights to you.

The first secret is often the hardest to manage: you need a good telescope. Mars is just about the most demanding telescopic object out there, and requires good optics. A telescope you pick up at the local mall or off eBay is very unlikely to come close to what's needed. Unfortunately many people fall into this trap and end up with nothing more than a plastic toy. Sad to say, the same amount of money, spent at a store specializing in telescopes, would yield a much more worthy telescope capable of a lifetime of satisfying observing. Since most of us aren't likely to find a telescope store at the local mall, you will probably need to seek out telescope stores online, and one of the oldest and most reliable is Orion Telescopes and Binoculars. The advantage of any telescope dealer, local or Internet, is that you can actually talk to them about what you want, and get good solid advice. They want you as a long term customer, and have a vested interest in making your first purchase a happy one.

For satisfying views of Mars, a telescope of 4 inches aperture is about the minimum I would recommend. With Mars, as with other astronomical objects, aperture rules, and any increase in aperture will pay real benefits in the quality of the view.

Because of the tiny size of Mars' disk, even at its closest, magnification is paramount. I've found that 200 power is the minimum with which to see the surface detail on Mars, and 300 power is even better. Good quality eyepieces are important, and often a Barlow lens is essential to get the necessary power boost.

Color filters are probably more useful for Mars than for any other planet. My favorite is the #21 orange or #23A light red. This tends to enhance the contrast of Mars' detail and also to cut some of the glare from its bright surface. A #80A medium blue filter is very useful for enhancing the high clouds that appear above the poles and along the limb of the planet.

Welcome to Mars Training Camp!
You can have the finest hardware in the store, and yet still have a disappointing first experience with Mars. The reason is that your eye and brain need to be trained in order to tease out faint detail at the limits of visibility. I've found that the best way of doing this is to make drawings of the planet at every opportunity.

"Oh, no," I hear you cry, "I'm not an artist!" Artistic skill is not a requirement; heaven knows I don't have any! What you are doing is attempting to copy, as accurately as you can, what you see on the disk of Mars. At first you won't see much, but as you concentrate, you'll soon be seeing more and more. As with deep sky observing, it sometimes helps to use averted vision, looking slightly off to one side of the planet.

While an ordinary HB pencil will do, you may get better results from a softer lead, such as a 2B. I find an "artist's stump" very useful. This is a tight roll of blotting paper sharpened at both ends, available from any artist's supply store. You use this to "smudge" the pencil lines, so that they take on a more realistic smooth shading. Finally an eraser with a sharp point is useful for removing shading to show white areas. Ordinary paper will do, but you can organize your observations better if you use a standard form, such as this one designed by Carlos Hernandez.

Start your drawing with a circle 40 mm in diameter to represent the disk of Mars. Except when very close to opposition, Mars shows a slight phase because the sunlight is coming from one side or the other; draw this in first. Then draw in the areas that change little as Mars rotates, namely the polar regions. Finally, draw in the darker shadings towards the center of the disk, and note the time. This is important, because Mars is rotating on its axis, and the apparent positions of surface features change fairly rapidly.

Your first sketches will be rough, but you'll find that they improve with each one you attempt. For each sketch, record at least the date and time; the observing form suggests a lot more data that can be recorded.

If you want to document your observation more thoroughly, use the blanks on the observing form. There are three circles for drawings: the left and right ones are for normal sketches, perhaps with and without a filter, while the middle one is for a diagram using numbers to indicate the darkness of features on a scale of 0 to 10. In order to compare observations around the world, dates and times are recorded in Universal Time (UT) which is a 24-hour clock based on the prime meridian in Greenwich, England. For example, if you made your drawing at 11:30 pm EST on November 3rd 2005, you would convert this to 04:30 on November 4th in Universal Time (5 hours later). ?Seeing? measures the steadiness of the image, usually with one of scales devised by Pickering or Antoniadi:

I = Perfect seeing, without a quiver
II = Slight quivering of the image with moments of calm lasting several seconds
III = Moderate seeing with larger air tremors that blur the image
IV = Poor seeing, Constant troublesome undulations of the image
V = Very bad seeing, hardly stable enough to allow a rough sketch to be made

"Transparency" measures how clear the sky is; oddly enough, a very hazy sky (transparency 1 or 2) often yields very good seeing, while a perfectly clear sky (6) is often hopelessly unsteady for seeing fine planetary detail. "CM," "Ls," "De," and "Ds" are discussed below.

As the Planet Turns
One final step is needed in order to compare your drawing to published maps like this one. You need to know what longitude on Mars was central on the disk at the time you made your drawing. You can do this easily using the Arkansas Sky Observatory?s Mars Physical Ephemeris Calculator. For example, for the drawing mentioned above, enter 11 04 2005 and 04h 30m in the ASO calculator, and you get a central meridian of 244.8°. You can then compare your drawing to the features visible at that longitude on the map. Careful studies of Mars sometimes use some other quantities, such as "Ls," which measures Mars? position in its orbit around the Sun, "De," the declination of the Earth as seen from Mars, and "Ds," the declination of the Sun as seen from Mars. These can be looked up in this table.

However, for a quick and easy picture of what Mars looked like at the time you made your drawing, check out a magnified view of Mars in Starry NightŪ at the time of your drawing, since the program does all the calculations for you automatically!

You should only compare your drawing to a map after you finish the observation, so as not to be influenced by what the map shows. At first, you will probably see nothing but vague smudges, but after a week or two of "training," you should be seeing much more detail. Some nights you may see nothing at all, and that may in fact be what is really there. The problem is with atmospheres: the atmosphere of Earth being unsteady and smearing the image of Mars, and the atmosphere of Mars sometimes carrying widespread dust storms which block our view of the surface. An online group like MarsObservers will keep you abreast of the weather and dust storms on Mars. The finest Mars observers on Earth post their images and drawings there every day, and there's always lively discussion of current events on the red planet.

A day on Mars, known as a "sol," is 39 minutes longer than a day on Earth. This means that if you observe Mars at the same time each night, the features on Mars will appear to drift in longitude because of Mars? slightly slower rotation rate. In fact it takes about 37 days before you will see exactly the same face of Mars at the same time.

Images of Mars
Taking good clear pictures of Mars has long been a major challenge to both professional and amateur astronomers alike. Making an exposure at the precise instant when the atmosphere is absolutely steady has been next to impossible. In recent years this has changed thanks to modern computer technology, and superb images of Mars are being taken regularly by a large number of amateur astronomers around the world. Their secret weapon is the lowly webcam. Using a webcam, you can make many exposures of Mars in rapid succession. Some will be good, some will be bad. If you discard the bad ones and combine the good ones in a computer process called stacking, you can produce an image that is much sharper than any of the images that went into it. Then programs like Adobe Photoshop allow you to further enhance the contrast and sharpness. The result is images which exceed the quality of anything that even the pros could manage more than a decade ago; some even come close to images taken with the Hubble Space Telescope.

Don't Give Up!
Although Mars is a challenging object for the amateur astronomer, it is ultimately very rewarding. It is the only planet whose surface we can observe directly, and it is the planet that most closely resembles the Earth.

September 2006

Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.

Details
Date Taken: 05/26/2011
Author: Geoff Gaherty
Category: Archives

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