Tumbleweed Observatory's

Astronomy Hints




How to Observe Mars, and What Kind of Telescopes are Useful

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Tips For Observing Mars

Mars has been a tantalizing solar system object since man first took note of the heavens. First, its confusing retrograde motion invited speculation. Then, when telescopes were trained on Mars, the initial views seemed to suggest seasons, perhaps plant life. Then, canals were imagined to have been seen. Then, the big letdown as depicted in this humorous Mars Probe Limerick, when our first spacecraft revealed a planet that looked more like the barren Moon than a planet paradise.

Yet we still watch with fascination, as every 26 months, the orbits of Earth and Mars bring them close together. It's called opposition, in that at that time, Mars is on the opposite side of Earth from the Sun.

Both Earth and Mars have elliptical orbits (more so for Mars), so the distance between the planets at closest approach varies.

Because of that, the apparent or angular size of Mars varies from one opposition to another. Mars never appears very big, but does on the average appear about the size of Saturn, minus the rings.

In numbers, Mars appears to be about 12 arc-seconds in size at the worst oppositions, and about 25 arc-seconds at the best. We had one of the best oppositions a few years ago in 2003. You can see the drawings I made when observing that opposition at Mars 2003 Opposition.

The anticipation of observing Mars is always high for me, but the experience often doesn't live up to expectations.


Martian dust storms.

Mars has some whoppers. Sometimes dust storms on Mars are global in coverage. Observing Mars during one of the global dust storms reveals nothing but a glowing, orange orb.

But now and again a Mars opposition is a beautiful thing. I can't explain why, but even though ample photographs of Mars exist from the great observatories, there's nothing quite like seeing a few faint details in your own equipment.

What You'll Need to Observe Mars

If you want to observe Mars, you need a telescope. For this observing, binoculars won't do. What kind of telescope?

You need an instrument that excels at high resolution. Light gathering power is not essential here, as Mars is plenty bright.

Planetary Positions

And, you'll need Mars to be as near to Earth as possible. This planetary position display obtained from the xephem planetarium program, shows tonight's position of the planets in their respective orbits around the sun.

In this diagram, the planets move in a counter-clockwise direction. When Earth, on the inside track, is catching up to Mars, then an opposition is coming. When we're approaching opposition with Mars, each day Mars will appear just a bit bigger.

If you see Mars more on the other side of the Sun from Earth, you can kind of forget seeing any details on Mars, as it's too far away.

xephem Data view

The table at left is the xephem Data Table for tonight. Among other things, it lists the current angular size of Mars. You can also check out the Sky and Telescope Mars Viewer to get an idea of what Mars features are observable on any given night.

The images below show what Mars will look like tonight at about 9:00 PM from Denver, CO. The Denver location was chosen to be a mid-US location, and the time was chosen to be a typical viewing time. The images are created using the Mars display from the Xephem planetarium program. The Map used for the display is an alternate Mars map donated by Bob Abraham.

The image on the left is a depicted view through a typical telescope using a star diagonal, such as a Cassegrain or refractor telescope. The view at right is a depicted view through a typical Newtonian telescope.

Xephem Mars Star Diagonal View
Star Diagonal View

Xephem Mars Newtonian View
Newtonian View

Best Option, A Quality Refractor

At left you see a comical t-shirt design called I Love My Refractor. It's a creed that many an amateur astronomer lives by. And for planetary viewing, a good refractor of moderate size and long focal length, like the Orion 9024 AstroView 90mm Equatorial Refractor Telescope, is hard to beat.

You might scoff at the idea of using such a small instrument for observing Mars. But some years ago, when Mars was about 17 arc-seconds in size at opposition, I used my modest 50mm refractor to get some very enjoyable views of the planet. I could make out, even with this small instrument, some of the major dark areas on the Mars. Using my 60mm f/17 refractor, I was able to see the Mare Acidalium feature of Mars in 2012. I considered that a pretty good result, in that on the date of the observation, Mars was only about 12.5 arc-seconds in apparent size -- half of the size of Mars during a most favorable opposition.

Refractors of long focal ratio, f/10 or better, make the best planetary telescopes. If you have a 60mm refractor, use it. You'll see a few details on Mars. You can read about some of the characteristics of refractors at Refractor Tutorial

While 60mm will show some detail on Mars, I recommend a 3 to 4 inch refractor for a better view. Larger refractors, while excellent for planetary observing, may be cost prohibitive.

Check out the Simulated View page for examples of what views (of Jupiter in this case) look like in different sized telescopes.

A Good Option, a Maksutov

A good option that is less expensive than a sizable refractor is a Maksutov Cassegrain, like the Celestron model pictured here. The Maksutov is a clever catadioptric design, using a corrector plate and mirror in combination to achieve superb images. All surfaces are spherical, making them easy to manufacture to high precision.

Maksutovs tend to have focal ratios around f/15, making them perfect for high resolution observing. The f/15 means that these telescopes have effective focal lengths that are 15 times their diameter. Long focal length telescopes give higher power for any given eyepiece than do short focal length telescopes.

The Maksutov's compact size makes the inclusion of a clock drive easy, and most are sold with that feature. You can get more information on the characteristics of Cassegrain telescopes at Cassegrain Tutorial

I've observed Mars, Jupiter, and Saturn extensively with my Meade ETX 90 and can attest to the high quality images produced by Maksutov optics.

Another good option is a Schmidt Cassegrain Telescope, like the Celestron NexStar 6 SE Telescope . These look similar to the Maksutov shown, but use a different design on the corrector plate. As a result, SCT's have focal ratios around f/10, and thus make pretty good general purpose instruments.

SCT's can give good planetary performance, enhanced by their short tube which gives good stability. They do have rather large secondaries however, which reduces the contrast on planetary images.

One of My Favorites -- the Long Focus Newtonian

If you are on a budget and still want to see Mars when it's close to Earth, I recommend a moderate to long focus Newtonian. Even a 4 1/4 to 4 1/2 inch Newtonian of long focus makes a quite good planetary telescope. Such instruments cost typically less than $300.

Shown is a typical 8 inch Dobsonian, a very popular telescope because of it's ability to see a large range of targets, and yet carry a modest cost. I use a specially designed 6 inch f/10 Newtonian on a Dobsonian mount. The telescope was designed by master telescope maker Steve Dodson. The instrument is descried in more detail on the Dob Review page. Additional characteristics of Newtonians are available at Newtonian Tutorial and Dobsonian Tutorial

Steve also makes a 4 1/4 inch long-focus DOB that makes a good, budget planetary telescope. You can see Steve's offerings at Stargazer Steve. Steve offers his telescopes as easy to assemble kits.

Finally, you can use any telescope of 3 inches or better diameter and see some details on Mars. But short focal ratio instruments have a few design issues that limit their capability for delivering superb planetary images.

You can use the following chart to see examples of telescopes for different types of observing. For seeing details on Mars and other planets, you'll want to concentrate on the general purpose and high resolution instruments.

The larger instruments will show you more with good observing conditions, but notice from the chart that with such instruments you'll be moving away from portability.

Now that You Have the Equipment

Here are a few tips to help you get the most out of observing Mars.

If you have an SCT or Newtonian, you want to have the alignment tuned as well as you can achieve.

Let the Telescope Cool Down

You need to let you telescope cool down to ambient temperature. For larger telescopes, this may take an hour or more.

Have a Steady Mount

You want a very steady mount on your telescope. There are some fine telescopes out there have have good optics, but inadequate mounts. The longer telescopes especially may be on inadequate mountings.

If you are observing at high power, a slight tap on the telescope should damp out in just a few seconds. If not, see what you can do to increase the sturdiness of the mount, or replace it. consider making one as i did on the Inexpensive Tripod page.

Use High Power Eyepieces

You'll need to magnify quit a bit to see mars, in excess of 100x. Better if closer to 200x or more. Any given telescope can only perform well at maximum magnifications of 50x per inch of objective diameter. Consider this when choosing a telescope.

Use the astro-customized search engine to find eyepieces and filters.

Custom Search

A Clock Drive is Nice

A clock drive is not necessary. Better to have a solid mount than a clock drive. That being said, it is more relaxing to be able to sit comfortably and have a clock drive keep the planet steady in the field of view.

Consider Filters

Consider using a filter for viewing Mars. The best filters for this purpose are ones made of glass that screw onto the bottom end of your eyepieces. A red filter can be useful for Mars in making the non-red features appear darker, increasing contrast for these features.

Don't be disappointed at the few details you see at first. Planetary observing takes persistence even on good nights. The atmosphere is rarely completely clear. Rather, clearing occurs now and again. You need to be watching to enjoy the benefit.

If you wish, get a drawing tablet and make some sketches. I've made a few and described my technique at Mars 2003 Opposition page.

Consider Mars Photography

2003 ETX90 Mars Image
Mars ETX90 Image, 2003
25 arc-sec size

2012 ETX90 Mars Image
Mars ETX90 Image, 2012
12.5 arc-sec size

You can even try some photography if you choose. I took the images above with my handy Meade ETX 90 Maksutov telescope. The image on the left was taken during the 2003 opposition when Mars was at a very favorable 25 arc-second apparent size. This image was taken using my Quickcam Express Astro- Camera conversion.

The image on the right was taken in 2012 when Mars was at a much less favorable 12.5 arc-seconds in apparent size. The camera used in this case was my Celestron NexImage astro-camera. I scaled the images to their apparent viewed sizes. In this comparison you can see that even at a small 12.5 arc-second size, the ETX 90 pulled out a few details. You can also see why astronomers get excited when Mars finally can be viewed and studied during a favorable opposition.

Mars is a difficult photographic target, however. You need to photograph through your telescope at high power. Even then, Mars will make a quite tiny image on film or CCD. Still, it is possible as you can see by the photo at left. This image was taken using my ETX 90 and my web cam conversion. The web cam produced an avi file with about 50 images in it. Stacking the images produced this image.

If it's a winter opposition, you may get your best views. Sometimes cold winter air gives extraordinary images. You'll need to be out awhile to see the most fleeting details, so dress warmly.