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What Would You Weigh On Mars, Plus Other Mars Data And Observing Tips

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Mars Interest, Then And Now

People are loaded with questions about Mars. Mars has often become a target of great interest, driven by both facts and fiction. There was the early speculation of canals on Mars, driven by the sketches of Giovanni Schiaparelli in 1877. While probably a misinterpretation of his report, it became believed that Mars had canals, and surely some intelligent beings had created them.

That led to the spectacular War Of The Worlds radio drama, produced by Orson Welles. That scary rendition of an invasion from Mars was so realistic that many people who listened to it were scared nearly to death, as they thought it was a real invasion.

Then, in the 1970's, our Mars Mariner spacecraft revealed a world that appeared more like the surface of the moon than a thriving planet of clever canal builders. And the Mars Viking program failed to definitely find even microbial life. Those disappointing results lead to a considerable drop off of interest for a couple of decades.

As scientists discovered ample numbers of Earth-based Extremophiles, they became excited about Mars again, as the extremophiles suggested that at least on Earth, life of a variety of exotic types can live in the most extreme conditions. Surely, something of like kind could make it on Mars.

Then followed ideas and hints of water on Mars, and scientists have long thought that where liquid water could exist, likely life could also. This lead to enough renewed interest to re-examine Mars, this time not from the top down, but the bottom up. That is, not to search for life at the onset, but for the fundamental requirements for life -- water most particularly.

Now we know, thanks to probes like the Phoenix Lander and the Curiosity Rover, that Mars is home to an enormous amount of ice, and so likely was awash with water some few billions of years ago. With all of that, Mars is a hot topic once again.

How Big Is Mars, And Other Interesting Facts

With renewed interest in the air, you may wonder about some aspects of Mars yourself. Like, how big is Mars? How far from Earth is Mars? How many moons does Mars have? And, the thing everyone wonders about, what would you weigh on Mars? (Hint, I could drop my diet in a flash). The following table has some of these interesting facts.

Dia (mi) 4221
Rel Dia (to Earth) 0.53
Rel Mass (to Earth) .108
Rel Gravity (to Earth) 0.38
Min Dist to Earth (mi*e6) 34
Max Dist to Earth (mi*e6) 249
Max Angular Size (arc-sec) 25.71
Min Angular Size (arc-sec) 3.49
Length of Day (hours) 24.6
Axis Tilt (deg) 25
Number of Moons 2

The table reveals some very interesting things about Mars, answering some fascinating questions. Like, how long is a Martian day? It's only about 40 minutes longer than an Earth day. And what is the tilt of Mars' spin axis? As the Earths tilts some 23.5 degrees to its orbital plane, Mars tilts at 25 degrees, surprisingly close to Earth's tilt. These two Martian parameters suggest an amazing similarity to Earth.

But there are significant differences. For example, Mars is only about half the diameter of Earth, and has only about 1/10 the mass of Earth. So what would a 200 pound man weigh on Mars, only 20 pounds? No, more like 76 pounds, as the smaller radius of Mars puts you closer to the gravitational center, giving Mars about 0.38 the gravity at the surface of the Earth.

As the table indicates, Mars has two moons, though Earth has but one. The moons were both discovered in 1877 by American astronomer Asaph Hall. They are named Phobos and Deimos. By our moon's standards, the moons of Mars are quite small. While Earth's moon is some 2163 miles (3481 km) in diameter, Phobos is only about 13.7 miles (22 km) in diameter, and Deimos even smaller at about 8.7 miles (14 km). Needless to say, Mars at some 4221 miles in diameter is visible from Earth even with naked eye, but the moons of Mars are not accessible with most amateur sized telescopes.

Like Earth, Mars goes around the sun. And, like Earth, Mars moves in an ellipse, a bit more flattened than Earth's ellipse, which is almost circular. Some times, as Earth and Mars proceed in their orbits, the planets are on opposite sides of the sun, making Mars up to 249 million miles away from Earth. It appears quite small then, at only around 4 arc-seconds in angular size. Still visible in an amateur telescope, but yielding few details.

At other times, Earth and Mars are on the same side of the sun, and when their respective ellipses are optimal, Mars is only about 34 million miles away from Earth. When this optimal geometry happens, Mars presents an apparent size of about 25 arc-seconds. In 2003, we had one of those optimal situations, and I was able to make the following Mars drawing with my 6 inch Dobsonian telescope, and take the photo of Mars with my Meade ETX 90 Maksutov.

Mars drawing and

Tips For Observing Mars

You can get into the excitement of viewing Mars, and you don't need your own space orbiting telescope to do it. As the above drawing and photo illustrate, you can see and even photograph Mars, especially at favorable oppositions, with amateur sized telescopes. I used a 6 inch reflector for the drawing above, but only a 3.5 inch telescope to get the photo. I've enjoyed observing Mars with as small as a 50mm refractor, and often with a 60mm refractor.

Be prepared, 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.

The diagram below shows the current relative positions of the inner planets (within the orbit of Jupiter). If Mars is opposite the Sun from Earth, don't expect much. But if Mars and Earth are on the same side of the Sun, especially if nearly at their closest approach, you're in for a treat.

planet positions

Inner Planet Relative Positions

In the above diagram, planets orbit in the counter-clockwise direction. Also realize that the Earth moves in its closer orbit faster than does Mars, so if Mars is ahead of Earth in a counter-clockwise sense, Earth is catching up. Otherwise, if Mars is close but clock-wise of Earth, Earth is pulling away.

In numbers, Mars appears to be about 12 arc-seconds in size at the worst oppositions, and about 25 arc-seconds at the best.

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. And, you'll need Earth and Mars to be positioned in their orbits such that they are relatively close together.

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 top is a depicted view through a typical telescope using a star diagonal, such as a Cassegrain or refractor telescope. The view at bottom is a depicted view through a typical Newtonian telescope.

Xephem Mars Star Diagonal View
Star Diagonal View

Xephem Mars Newtonian View
Newtonian View
Apparent Size:

Best Option, A Quality Refractor

I Love My Refractor T-shirt

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.