Mars Observing FAQ and Links

2020 Opposition:

Closest Approach: October 6
Opposition: October 13

Some sizes for the month after opposition: How fast does Mars shrink after an opposition?

October 16	22.3"		November 6	19.3"
October 23	21.6"		November 13	18.0"
October 30	20.6"		November 20	16.7"

The view favors Mars' southern hemisphere, which will be experiencing summer around the time of opposition, so the south polar cap isn't very visible.

Here are the slides for a talk I gave on Observing Mars at Opposition on October 16, 2020 for the PEEC Planetarium in Los Alamos, NM (press spacebar or → to advance to the next slide).

If you prefer, you can skip the FAQ and jump directly to the links.

Mars Observing FAQ

Q. What's an opposition, and why do I care?
A. Opposition is when an outer planet is opposite the sun as seen from earth; i.e., when it is closest to us. A planet appears bigger at opposition, and details are easier to see than at other times. In the case of Mars, the difference in size and visible detail is dramatic.

Note that the month or so after the opposition is also a good time to observe; although the planet will be starting to recede, it will be rising earlier in the evening than at opposition, which makes it easier for most people to observe it when it's high in the sky.

Q. What sort of equipment do I need to look at Mars?
A. Just about any telescope will do. I've seen some detail on Mars, during the 1997 opposition, with my 4.25" f/4 reflector, though that's certainly not an ideal planetary telescope. A good 6" f/8 reflector or 4" refractor should show a lot of Mars detail if the air is steady and if the telescope is in good collimation. I've also gotten excellent views of Mars through big dobsonian reflectors: although a clock drive is convenient for high magnification observations, don't let that stop you if you happen to have a dob. In 2003 I've done most of my observing so far with my homebuilt 8" dobsonian.

Binoculars won't show you any more than you see with the naked eye: just a bright red point.

Steady air and magnification are more important than telescope aperture, ultimately; you'll have the best luck when Mars is high in the sky, and it may help to find a location at high elevation or at least one where you're not looking over houses, cars or asphalt.

Q. Do I need filters to observe Mars?
A. No, but they can sometimes help in bringing out detail. They're especially helpful if you have an inexpensive refractor which has some chromatic aberration (meaning that it shows some colored fringes around bright objects): filters can dramatically cut down the color fringing. See specifics on the ALPO page.

Q. What can I see with a small telescope?
A. Hellas (a bright impact basin), some dark features like Syrtis Major, Mare Erythraeum, Mare Acidalium, and Niliacus Lacus, more subtle dark features like Margaritifer Sinus, Sinus Sabaeus, Lacus Solis (the "Eye of Mars"), and the polar caps.

With filters, you can sometimes see clouds and hazes of various types. With exceptional seeing, there are many other light and dark features which become visible, and you can look for details on the edges of the features, and for clouds over the Tharsis volcanos. You may even see parts of Valles Marineris, near Lacus Solis.

Sorry, you won't see canals -- there aren't any. But there's plenty of other stuff to look at!

Q: Why can't I see anything at all?
A: Mars is small. Really small. The details are smaller still. You really have to practice and have patience. The details will come, but don't expect them to be easy. Try for the polar cap first: that's usually the easiest to see. Then try to see some dark markings on the planet. The more you observe the planet, the more you'll learn how to see the detail on it.

Q. How can I train my observing skills?
A. Observe a lot -- start well before the opposition if you can, even if Mars is small or low in the sky. That way, by opposition you'll be ready to see all the detail which is there.

Also, try sketching the detail that you see -- even if you don't consider yourself an artist (I'm certainly not), sketching planetary detail really helps you think about what you're seeing, as well as being fun in its own right.

Q. Why do I see two polar caps, or none, when everybody says only one is visible?
A. First, in some oppositions both polar caps are visible; in others, only one is.

Hellas, a light-colored impact basin (one of the biggest in the solar system) which tends to accumulate frost and haze and consequently appears very bright, looks more like a polar cap when it's near the limb than the real polar cap does. If it looks like you're seeing two polar caps, the other one may be Hellas. If it looks like you're only seeing one, it may be Hellas rather than the polar cap, especially during the Martian summer when the polar cap is unusually small and difficult to see.

If you're not seeing any polar caps, it may be that it's summer in the hemisphere pointing toward us, and the polar cap has shrunk to a point where it's hard to see.

Q. How do I figure out what part of the planet I'm looking at and how it's oriented at the time when I'm looking?
A. That's one of the tricky parts of observing Mars, especially during this opposition when the polar cap is expected to be inconspicuous.

One way is to use a Mars globe, if you can find one (see the Links section for some suggestions).

The other, and easier, method of orientation is to use a computer program. See the software links below for programs which show Mars rotated correctly for a particular time and date.

Q. Can I see Mars' moons?
A. The moons should, in theory, be visible in large amateur telescopes (say, a 10" or so), but they're quite difficult, because they're very close to Mars and Mars is so bright its glare overwhelms the dim moons. Phobos is brighter, but Deimos is farther from Mars so might actually be easier to see. It helps to move Mars just out of the field, or to use an "occulting bar" in the eyepiece to block out the brightness of Mars. It's a challenge, but it's definitely possible!

... Mars Links ...

Software packages that show Mars' surface features

Any decent planetarium program will show Mars' location in the sky, but not many show its surface features and correctly calculate which features are visible at a particular time. Here are some that do:

Free Online

• Marsmap, my JavaScript Mars simulator.
• JPL's space simulator Views of any solar system object as it looks at a specified time. Unfortunately, it doesn't show much detail on Mars so I haven't found it very helpful for figuring out which features are pointed toward us at a given time. No feature labels.

Non-Free Planetarium Programs

• Sky Safari for Android and IOS
• Starry Night for Mac and Windows

Older programs, no longer supported, but will still work if you can get a copy:

• XEphem No longer sold as a paid app, but you can still download the source (for free) and compile it.
• Guide A Windows planetarium program, not free, not sure if it's still sold
• Sky & Telescope Mars Previewer: Windows-only freeware

Labelled Mars Maps Online

• My color Mars map, plus east-west flipped and north-south rotated versions courtesy of Bill Arnett. I made these by adding labels to an unlabeled JPL Mars map.
• My modified ALPO Mars map, with drop shadows on the white labels and a few label corrections. Included here by permission of the ALPO map copyright owners, Daniel M Troiani and the Association of Lunar & Planetary Observers - Mars Section.
• BAA Maps of Mars A nice assortment of different maps.
• Color Mars map by Damian Peach; Damian Peach original Mars Map
• Mars ALPO Albedo Map (black and white)
• Ralph Aeschliman has a selection of lovely airbrushed Mars maps
• National Geographic Mars Map (see also their false-color Martian Map).
• Cylindrical Planetary Maps on the Internet from Wm. Robert Johnston has a good Mars list
• Map of NASA's Mars Landing Sites.
• USGS Geologic Map of Mars: not so great for observing but wonderful if you like geology. This one's also good and maybe a little more readable: Geologic Map of Mars.

Make Your Own Globe

• USGS Mars Maps & Globes This site has kits to download and build an excellent Mars globe from a PDF made from Mars Viking and Global Surveyor mosaics. Excellent! The Mars Viking Image Mosaic Globe is the best for observers.
• Making globes of the planets, a complete set of planet globes images, complete with two perl options for making your own (one is a GIMP plug-in, the other is a standalone script).
• Make Your Own Mars Icosohedron Globe: Unlabeled, but you could write in your own labels.

Unlabelled Mars Maps Online

• NASA Mars Trek: You can pan and zoom in and out and view a huge selection of overlays, but it doesn't have the option of showing you Mars as seen from Earth. To add labels, look for the symbol in the lower right corner that pops up "Basemaps" when you mouse over it. Open it and flip the switch in the upper left of the box that says, "nomenclature".
• MGS MOC Mars Map a high-res map of Maps using Global Surveyor images
• JPL Mars maps
• National Geographic map
• NASA Mars Atlas
• Nicolas Biver's sketch albedo map

Places to buy Mars Maps and Globes

• Replogle makes my favorite Mars globe; it's 4", shows albedo features and used to be sold in toy stores in an inexpensive set with a (marginally useful) moon and (fairly poor) earth globe. Unfortunately it has become very difficult to find; I've heard that it's possible to buy these from Replogle in quantity and someone may be reselling them on ebay, so try searching ebay for "mars globe".
• Sky Publishing sells a few Mars Globes, including one that's small and reasonably priced.
• Hugg-A-Planet Mars Stuffed, and looks like the labelling is quite good.
• WARD's World has an excellent looking Mars globe, but it's quite expensive
• The RASC Observer's Handbook has a decent B&W Mars map and lots of observing info (lots of great info on observing other objects, too).

Pages for Past Oppositions

In some years I've put up detailed observing info for that particular year. Specifically: Mars 2007 • Mars 2005 • Mars 2003.