The Mars Observer’s Tool Kit

Geoff Gaherty







What’s to look at?

The 2003 apparition of Mars promises to be a most exciting astronomical event. For over a month Mars will be larger than it as been at any time in the past 15 years, and for a few days in late August it will be closer than it has been in thousands of years. Despite this being a particularly favourable apparition, Mars may still seem disappointingly small to many observers who are used to seeing photographs made from space. Yet there is much for the trained eye to see, and for the talented photographer to image.

Mars is the planet in the solar system most similar to our Earth. It has an atmosphere, it has ice caps, and it has weather, all of which can be seen and imaged with amateur telescopes. What we can’t see are the topographic features captured by space missions; our view of Mars is just like our view of the Full Moon: the Sun lighting its surface is almost directly behind us, so shadows are as invisible as at high noon in the desert. All we can see of Mars’ surface, aside from its bright white polar caps, is a pattern of light and dark shadings, called albedo features, similar to the maria of the Moon.

One thing to remember about Mars is that it’s a planet in motion. It rotates on its axis slightly more slowly than the Earth, so that its day is slightly longer. The effect of this is that after 24 hours have passed on Earth, Mars hasn’t quite rotated to the same position as it was in 24 hours earlier; in fact it’s about 10 degrees short of a full rotation. The result of this is that if you observe Mars every night at exactly the same time for a week, its surface features will appear to drift from night to night in the opposite direction to the actual rotation of the planet. It will be slightly more than a month before the same face of Mars will be visible at the same time on Earth.

Mars is also moving in its orbit around the Sun. Its pole is tilted away from the ecliptic slightly more than Earth’s, and in a different direction, towards Deneb rather than Polaris. This summer and fall, Mars’ southern hemisphere will be tilted towards us. Spring equinox in its southern hemisphere was on May 6, and summer solstice will be on 2003 September 29, about a month after opposition. Yes, the seasons on Mars are almost twice as long as those on Earth because of its longer year. So this year we will mainly be viewing Mars in its southern late spring and early summer. The south polar cap (SPC) will be prominent, but gradually shrinking in the heat of the Sun. The north polar cap (NPC) itself will be hidden from us, but the north polar hood (NPH), the cloud and haze near the north polar cap, may be visible.

For more detailed information on the 2003 apparition of Mars, see:

http://www.tnni.net/~dustymars/2003_MARS.htm
http://www.arksky.org/mars2003.htm
 

What equipment do I need?

A telescope, of course. Because of the tiny disk that Mars presents to us, less than half the size of Jupiter at its largest, this telescope needs to be of excellent quality and equipped with good quality eyepieces allowing magnifications of at least 200x. For satisfying views of the Martian features an aperture of at least 100mm for a refractor or Maksutov, and 150mm for a Newtonian or a Schmidt, is needed. Certainly you can observe Mars with smaller scopes, but your views will be limited. Many observers find colour filters very helpful for observing Mars, especially red (25), green (58), blue (80A) and violet (47). The first and last may be too dense for use with smaller apertures; an orange (21) may be substituted for the red, and the violet done away with entirely. A solid mount is essential for planetary observation, and one with equatorial tracking is highly desirable. More specific equipment requirements will be discussed below.
 

Observing projects

1) Disk Drawings

The traditional way of observing Mars is to make a pencil sketch of what you see at the eyepiece. Artistic talent is not required; simply try to transfer onto a piece of paper what you see on the planet. There are two reasons for making a sketch. First, it is your record of what you saw, and will bring that view back to your mind much more vividly than any written description; one picture is indeed worth a thousand words. Secondly, and even more importantly, the concentration involved in trying to catch glimpses of detail to transfer onto paper will gradually train your eye to see more detail than appears at first glance. Despite the advances in imaging, drawings of Mars are still scientifically useful, as well as being personally satisfying.

In order to record observations in a systematic way, it’s very helpful to use a standard form like this:

http://www.gaherty.ca/rogers/Marsobservingform.pdf

The circles represent the disk of Mars. It’s important to record the date and time of each observation, along with other details of the observation, so that you can compare your drawing with others. I’ll give details of how to fill out the form at the end of this article.

Use a regular white flashlight rather than a red one to illuminate your drawing paper. You need to remember that Mars is rotating just like the Earth, and the surface details will appear to shift noticeably if you take too long to make your drawing. The trick here is to first draw the features which show little movement. Except very close to opposition, Mars shows a definite gibbous phase; this should be the first thing you draw. At the same time, establish the directions in your telescope and mark them on your drawing. If you’re not sure of your directions, move the telescope tube slightly towards Polaris; this will tell you which way is north in the eyepiece. Even if you have a motor drive, turn it off for a few seconds and note the way Mars drifts in the eyepiece. Mark the leading edge on the drawing "p" for "preceding," and the trailing edge "f" for "following." These terms are less ambiguous and less liable to be confused than east and west.

Next draw the polar caps and the clouds which possibly surround them. I usually draw these in with a dotted line. I find a soft pencil, such as a 2B, to work best. Then try to place the darkest markings you can see in their correct locations on the disk...just shade them in roughly. Once you’re satisfied with their positions, note the time and use this as the "official" time of your drawing. Now proceed to fill in the finer details, waiting to glimpse them in moments of good seeing. Place them in relation to the dark markings you first drew, as these are your reference points. A tool I find very useful for making smooth and realistic shadings of the Martian surface is an "artist’s stump." This can be purchased very inexpensively from an art supply store: it is a tight roll of blotting paper shaped like a pencil and sharpened at both ends. You first lay down some graphite on the paper by lightly shading with a soft pencil, and then use the tip of the "stump" to blend his shading into a smooth finish. The appearance of my drawings improved 100% once I started using a stump.

Once you’ve finished your drawing, you may want to add intensity estimates and/or observations through filters (see below). You should fill in the information on the observing form and make any notes while everything is fresh in your mind.

Close to opposition, when Mars is well placed for much of the night, you may want to make more than one drawing in an evening, since the features on Mars will have rotated significantly in an hour or two, bringing new longitudes into view. Objects on the preceding limb are rotating away from you, and new objects will appear on the following limb. Use a second form for this additional drawing.
 

2) Intensity Estimates

Instead of, or in addition to, a shaded naturalistic drawing of Mars, you may want to make estimates of the intensity or darkness of various features that you observe. This is done on a rough sketch, more like a diagram, and looks a bit like a "paint-by-numbers" kit. You indicate the brightness and darkness of the observed features on a scale of 0 to 10, where 0 is defined as the black sky background and 10 is the most brilliant feature, usually the south polar cap. There is a circle on the observing form for recording intensity estimates.
 

3) Observations Through Filters

After you’ve observed Mars in normal white light, you may want to re-examine it with coloured filters, looking for differences in the appearance of features in different colours. A red filter increases the contrast of the dark maria markings. A blue filter is good for enhancing atmospheric features such as clouds and haze. A violet filter may reveal the "blue clearing," an unusual transparency in Mars’ atmosphere which occurs at times allowing dark features, normally invisible in this filter, to be seen as readily as they are without the filter.

If there is a significant difference between your first drawing in white light and the view through one of the filters, you may want to make a drawing through the filter. Be sure to note the time of the filtered drawing separately from that of the main drawing.
 

4) Imaging

For most of the 20th century, Mars was an extremely challenging object to photograph well from Earth, and even photographs from professional observatories showed only a fraction of what was visible to an amateur visual observer. The arrival of digital imaging has changed all that, so that amateurs today with very inexpensive equipment are obtaining images superior to any images possible from Earth two decades ago. Five years ago, a handful of amateurs with expensive CCD cameras started making outstanding images. Thanks to advances in hardware and software, images of similar quality can now be made with commercial digital cameras, video cameras, and even the lowly webcam. In fact, some of the finest images today come from webcams, multiple images combined by stacking them with computer software. Almost any digital camera can do better than film, though certain cameras, such as the Philips ToUcam Pro, seem to be particularly well suited for this work. The people producing these images are breaking new ground; the best way to learn to do what they are doing is through several active groups on the internet:

http://groups.yahoo.com/group/marsobservers/
http://groups.yahoo.com/group/QCUIAG/
http://groups.yahoo.com/group/digital_astro/
 

What should I do with my observations?

Once you’ve made some observations of Mars, you may want to share them with other Mars observers. The primary place to do this in North America is the Mars Section of the Association of Lunar and Planetary Observers:

http://www.lpl.arizona.edu/~rhill/alpo/mars.html

Organizations like the ALPO collect Mars observations of all types from around the world and combine them into detailed reports giving an overview of the whole apparition.

You may also want to submit your observations to some of the on-line groups, such as the Yahoo Mars Observers group:

http://groups.yahoo.com/group/marsobservers/

If you send them to me, I will try to get them posted in the Observing section of the RASC’s web site:

http://www.rasc.ca/observing/sections.html

Even if you don’t want to submit your observations, you probably will be interested in trying to match what you saw with the named features on Mars. The ALPO map of Mars shows the major observable features, and appears on page 189 of the Observer’s Handbook. It is also available on-line at:

http://www.lpl.arizona.edu/~rhill/alpo/marstuff/B&WMarsmap.jpg

You can also get a simulated image of Mars for any particular date and time from:

http://www.kk-system.co.jp/Alpo/kk/Ms2003/MSmenu.htm

Appendix: Mars Observation Form

http://www.gaherty.ca/rogers/Marsobservingform.pdf

Time and date: Times and dates should always be recorded in Universal Time (UT). This is a 24-hour clock used extensively by astronomers and meteorologists, among others, and is based on the local time at the Earth’s prime meridian, 0° longitude, in Greenwich, England. This removes the ambiguities of local time zones and daylight time so that observations made everywhere in the world can be directly compared. Most time zones in the world (but not all, Newfoundland for example) are offset from Universal time by an exact number of hours. In North America, 00:00 UT occurs in the afternoon or early evening, so that by the time most of us start observing, it is already tomorrow’s date in UT. The following table should help you figure out what the current time and date is in UT:
 
UT     NST AST EST CST MST PST
  NDT ADT   EDT CDT MDT PDT  
Aug 3
23:00
Aug 3
20:30
Aug 3
20:00
Aug 3
19:30
Aug 3
19:00
Aug 3
18:00
Aug 3
17:00
Aug 3
16:00
Aug 3
15:00
Aug 4
00:00
Aug 3
21:30
Aug 3
21:00
Aug 3
20:30
Aug 3
20:00
Aug 3
19:00
Aug 3
18:00
Aug 3
17:00
Aug 3
16:00
Aug 4
01:00
Aug 3
22:30
Aug 3
22:00
Aug 3
21:30
Aug 3
21:00
Aug 3
20:00
Aug 3
19:00
Aug 3
18:00
Aug 3
17:00
Aug 4
02:00
Aug 3
23:30
Aug 3
23:00
Aug 3
22:30
Aug 3
22:00
Aug 3
21:00
Aug 3
20:00
Aug 3
19:00
Aug 3
18:00
Aug 4
03:00
Aug 4
00:30
Aug 4
00:00
Aug 3
23:30
Aug 3
23:00
Aug 3
22:00
Aug 3
21:00
Aug 3
20:00
Aug 3
19:00
Aug 4
04:00
Aug 4
01:30
Aug 4
01:00
Aug 4
00:30
Aug 4
00:00
Aug 3
23:00
Aug 3
22:00
Aug 3
21:00
Aug 3
20:00
Aug 4
05:00
Aug 4
02:30
Aug 4
02:00
Aug 4
01:30
Aug 4
01:00
Aug 4
00:00
Aug 3
23:00
Aug 3
22:00
Aug 3
21:00
Aug 4
06:00
Aug 4
03:30
Aug 4
03:00
Aug 4
02:30
Aug 4
02:00
Aug 4
01:00
Aug 4
00:00
Aug 3
23:00
Aug 3
22:00
Aug 4
07:00
Aug 4
04:30
Aug 4
04:00
Aug 4
03:30
Aug 4
03:00
Aug 4
02:00
Aug 4
01:00
Aug 4
00:00
Aug 3
23:00
Aug 4
08:00
Aug 4
05:30
Aug 4
05:00
Aug 4
04:30
Aug 4
04:00
Aug 4
03:00
Aug 4
02:00
Aug 4
01:00
Aug 4
00:00

Thus, if for example you made an observation of Mars at 10pm EDT on August 3, you would record the date and time on the form as 02:00am UT on August 4. For more information on time, see the Observer’s Handbook, page 35.

Central Meridian (CM): This is the Martian longitude of the imaginary line on Mars connecting the two poles and bisecting the disk at the time of the observation. Longitudes on Mars are measured from 0° the "bay" between the two forks of the Sinus Meridiani. The CM is essential for comparing drawings made at different times, and for looking up features on published Maps of Mars. It can be calculated from information on page 187 the Observer’s Handbook or, more simply, by using this on-line calculator:

http://www.arksky.org/cgi-bin/mars_eph.pl

Filter: Indicate any filter used here. "Wratten" refers to the standard Kodak Wratten filter designations, such as 25, 58, 80A, 47, etc. Most filters are labeled with these designations.

Intensity Estimates: See above.

Ls, De, Ds: Leave blank.

Instrument: Your telescope’s aperture and type: RR = refractor, RL = reflector, CAT = catadioptric.

Magnification: List in order most used.

Seeing: The steadiness of the atmosphere. This can be measured on the ALPO scale:
 
1-3 Very Bad
4-5 Poor
6-7  Good
8-10 Excellent

Or the Antoniadi scale:
 
I Perfect seeing, without a quiver.
II Slight undulations, with moments of calm lasting several seconds.
III Moderate seeing, with large tremors.
IV Poor seeing, with constant troublesome undulations.
V Very bad seeing, scarcely allowing the making of a rough sketch.

Transparency: The clearness of the atmosphere. This can be measured on a scale from 1 to 6, roughly equivalent to the faintest star visible near the zenith with the naked eye, and/or with the words on the form.

Notes: Add any descriptive notes which will expand and explain your observation.
 

Revised 2003-07-23