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.
Why?
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.
If you want to find a good deal on Astronomical equipment,
use this astro-customized search engine:
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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.
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.
Best Option, A Quality Refractor
At left you see a popular size refractor. It is similar but bigger than my
classic f/15 design achromatic refractor.
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 instrument 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.
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, or SCT. 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.
Telescope/Observing Preference Table
Use this astro-customized search to browse some excellent telescope
vendors.
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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.
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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.
You can even try some photography if you choose. Mars is a difficult 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.
