The rapid approach of summer in the northern hemisphere of Mars shows the North Polar Cap shrinking at lower right with a dark Lowell Band surrounding it, and with the Lemuria detachment of the polar cap next to the band. Orographic clouds can be seen over Elysium Planitia in the center of the disk and over Olympus Mons on the edge at lower left. Gomer Sinus are the two protrusions from Mare Cimmerium above Elysium at top. Syrtis Major is the large dark area rotating into view at upper right. Clouds can also be see in Lybia next to Syrtis Major. This image was taken with a Celestron 11 Inch Edge HD f/10 Aplanatic Schmidt Cassegrain working at f/29 at 8,102 mm focal length with a 2.9x Barlow with a Canon EOS T2i (550D) with 4.3 micron pixels. The sampling was at 0.11 arcseconds per pixel. It was shot with 640 x 480 Movie Crop Mode at 60fps with a 1/60th second exposure at ISO 400. The video was 4 minutes and 4 seconds long and contained 12,632 frames. At the time of the image Mars's equatorial diameter was 13.7 arcseconds and it shone at magnitude -1.1 at an altitude of 59 degrees. The image was stacked in AutoStackkert!2, Sharpened in Registax 6 and further processed in Photoshop CS5.

Mars is the fourth planet from the Sun. It was named after the Roman God of war, probably because its red color which comes from the iron oxide (rust) in its soil.

It takes 686.971 Earth days for Mars to complete one orbit around the Sun.

Mars rotates on its own axis once every 1.025,957 Earth days or every 24 hours 37 min 22.66 sec. The length of a day on Mars is very similar to the length of a day on the Earth. To see the same feature on the central meridian of Mars, you must view it about 37 minutes later each day.

Mars has a diameter of 6,792.4 km (4,220.6 miles), about roughly half of the Earth's diameter of 12,742 km (7,917 miles).

Mars's brightness can vary from magnitude +1.6 to -3.0, and its size can vary from 3.5 to 25.1 arcseconds.

Although Mars appears as a biologically inactive world today, there is evidence that Mars has water, and in the past may have had rivers, lakes and even an ocean.

Imaging Mars

Because Mars's orbit lies outside of the orbit of the Earth, it comes to opposition when it is opposite the Sun in the sky and nearest to the Earth when it has its largest apparent diameter from our viewpoint. Mars can also exhibit phase effects depending on its location in relation to the Earth. Detail on Mars is best seen in the months around opposition, and particularly at those oppositions when Mars is closest to the Earth. Mars comes to opposition once every 764 to 812 days.

Syrtis Major is the largest dark albedo feature at upper right. Libya is the light plain next to Syrtis Major at top center of the disk of Mars. The morning limb at lower left has limb haze and just to the right are orographic clouds over the volcano Elysium Mons. Clouds can be seen over Hellas Basin at top. The north polar cap is at lower right. This image was taken with a Celestron 11 Inch Edge HD f/10 Aplanatic Schmidt Cassegrain working at f/29 with a 2.9x Barlow at 8,102 mm focal length with a Canon EOS T2i (550D) with 4.3 micron pixels. The sampling was 0.11 arcseconds per pixel. It was shot with 640 x 480 Movie Crop Mode at 60fps at 1/60th second exposure at ISO 400. The video was 3 minutes and 2 seconds long and contained 10,955 frames. At the time of the image Mars's equatorial diameter was 13.8 arcseconds and it shone at magnitude -1.1 at an altitude of 55 degrees. The video was stacked in AutoStackkert!2, sharpened in Registax 6 and further enhanced in Photoshop CS5.

Mars has a highly elliptical orbit. Because of this its size can vary greatly at opposition. When it is closest to the Sun at perihelion and also at opposition to us at the same time, it will be closest to us and therefore have its largest apparent size. Favorable perihelic oppositions came at 15.8-year intervals and occur between late July and late September.

At the perihelic opposition in August of 2003, Mars subtended an apparent size of 25.1 arcseconds. By comparison, during the 2012 opposition, when the images in this section were taken, Mars's maximum apparent size was only 13.88 arcseconds in diameter.

The declination tells you how high above, or below the celestial equator that Mars will be at opposition. This tells you how high in the sky the planet will be when it transits the meridian. For northern hemisphere observers, a positive declination puts Mars higher in the sky. The reverse is true for the southern hemisphere.

Martian Geologic and Surface Features

In a telescope, Mars's surface can display a wealth of detail. You can see and resolve more in an image if Mars is closer and larger.

Unlike Venus, Mars has a very thin atmosphere and the surface is easily visible, revealing some of the most interesting planetary detail in the solar system. Mars has fascinating surface details that can be observed and photographed, such as polar ice caps, volcanoes, light and dark albedo features, deserts, and clouds. Dust storms can sometimes even obscure much of the surface of Mars and last for long periods of time.

The Tharsis region is centered on the planet in this image. Mare Acidalium is the dark area to lower left. Solis Lacus, Aurorae Sinus and Mare Erythraeum are at top. Amazonis Planitia is at right. The north polar cap is visible at bottom on the planet. Taken with a Celestron 11 Inch Edge HD f/10 Aplanatic Schmidt Cassegrain working at f/20 with a 2x Barlow at 5,588 mm of focal length with a Canon EOS T2i (550D) with 4.3 micron pixels. Sampling was at 0.158 arcseconds per pixel. The Live View was recorded with Images Plus Camera Control as an SID file format shooting at 1/100th second exposure at ISO 400. The video contained 658 frames. At the time of the image Mars's equatorial diameter was 13.5 arcseconds and it shone at Magnitude -1.0 at an altitude of 58 degrees. The video was converted to BMPs and stacked in AutoStackkert!2, sharpened in Registax 6 and further enhanced in Photoshop CS5.

The following features are visible on Mars:

• Polar Caps

  Mars's polar caps are one of its most striking, prominent, and distinctive features. Mars has polar caps at both the north and south poles. They are comprised mostly of water ice. The northern polar cap sits in the Planum Boreum, the Northern Plain. The southern polar cap sits in the Planum Australe, the Southern Plain. These polar caps grow and recede, depending on the season on Mars. Both have a permanent cap made of water ice as well as a seasonal one made of carbon dioxide that forms in the winter. In the spring and summer, the seasonal polar cap sublimates leaving only the permanent cap.

  Just as with the Earth, when it is summer in one hemisphere on Mars, it is winter in the other. So as one polar cap shrinks, the other grows. When Mars is near perihelion (closest to the Sun in its orbit), the southern hemisphere experiences summer, and the north winter. When Mars is farthest from the Sun at aphelion, it is summer in the northern hemisphere and winter in the south. Because Mars's orbit is highly eccentric, there is a large difference in distance from the Sun at perihelion and aphelion, and southern winters last longer than northern winters. This causes the seasons in the southern hemisphere to be more extreme than in the north. This lead to more interesting variations in the southern polar cap. During the winter season, a hood of clouds can also form of the poles, called a polar hood. Dust storms on Mars also tend to occur when the planet is closest to the Sun at perihelion.

  When the polar caps start to shrink, a dark banding can be seen around them called "Lowell Bands". Orographic clouds, made of water vapor, also increase at this time over the volcanoes in the afternoon in the summer. As the caps shrink more, parts of them detach around the edges.

• Albedo Features

  As seen from the Earth, Mars has large light and dark albedo areas on its surface. Albedo is a measure of reflectivity. Lighter dust-covered plains contain sand with iron oxide that gives them a distinctive reddish color. Darker features are compositionally different and reflect less light because winds have swept the dust away revealing the underlying rock.

  The face of Mars that is visible for observation or photography can be found with WinJUPOS or Sky & Telescope's Mars Profiler web application.

  When Mars is large enough, and the seeing good enough, the polar caps and dark albedo features are the first things to be seen. Syrtis Major is the largest, most distinctive, and probably the best known dark marking on the surface of Mars.

  Looking something like the continent of Africa on Earth, Syrtis Major Planum (it's official name) is a large shield volcano, formerly thought to be a plain. Syrtis Major gets its dark color from volcanic basaltic rock.

• Hemispheric Differences

  The northern and southern hemispheres of Mars are quite different. About one third of the northern hemisphere is at a much lower elevation than the remaining two thirds in the south. This is similar to the Earth's ocean basins, although Mars's lowlands are not full of water presently. The southern highlands are heavily cratered and very old. The northern lowlands are flat and smooth, with few craters. The crust in the southern highlands is also almost twice as thick as in the northern lowlands.

• Volcanoes

  Mars has the largest known volcano in the solar system, Olympus Mons, at 27 km in height (16.77 miles). It is extinct. There is no current volcanic or tectonic activity taking place on Mars. Olympus Mons can sometimes be seen in high-resolution images poking out through the orographic clouds around the summit. Olympus Mons is located, along with several other large volcanoes, in Tharsis, a region between the lowlands of the north and highlands of the south.

  The Tharsis region is an elevated portion the surface of mars. The Tharsis bulge covers 25 percent of Mars surface. It is full of volcanoes including Ascraeus Mons, Pavonis Mons and Arsia Mons, three volcanoes known as the Tharsis Montes on the crest of Tharsis. Olympus Mons is located just off the northwestern edge of the Tharsis bulge.

  Giant fractures extend outward from Tharsis, going halfway around the planet. These were probably caused by the stress placed on the planet's crust by the mass of Tharsis.

  Elysium is another smaller volcanic region far to the west of Tharsis containing Elysium Mons, another volcano.

• Impact Basins

  Mars's southern highlands also include several very large impact basins. Hellas Planitia is 1,800 km (1,118 miles) in diameter, Isidis is 1,000 km (621 miles), and Argyre is 800 km (497 miles). Utopia Planitia is 3,300 km (2,050 miles) in diameter in the northern lowlands, but it is completely buried by northern plain deposits.

Martian Clouds and Hazes

Clouds can be found in many locations on Mars. Most clouds that form on Mars are related to the sublimation of carbon dioxide and water ice in the polar caps, and the subsequent movement of these gases and vapors to areas where they eventually condense into clouds. Winter ice clouds on Mars are white but other hazes can be blue.

Mars is seen here showing an unusual terminator projection (arrowed), discovered by Wayne Jaeschke. The feature may be a high altitude or mesospheric cloud at an altitude of 40-80 kilometers above the surface illuminated by the Sun making it look projected from the planet because the area under it is still in shadow on the terminator. Volcano Olympus Mons can be seen just to the left of the center, surrounded by orographic clouds. Other clouds are visible to the left over Tharsis. The north polar cap is at the bottom with a dark Lowell band next to it. This image was taken with a Celestron 11 Inch Edge HD f/10 Aplanatic Schmidt Cassegrain working at f/29 with a 2.8x Barlow at 8,102 mm of focal length with a Canon EOS T2i (550D) with 4.3 micron pixels. It was shot with 640 x 480 Movie Crop Mode at 60fps at 1/60th second exposure at ISO 400. The video was 6 minutes and contained 21,547 frames. The sampling was 0.11 arcseconds per pixel. At the time of the image Mars's equatorial diameter was 13.3 arcminutes and it shone at magnitude -0.9 at an altitude of 59 degrees. The video was stacked in AutoStackkert!2, sharpened in Registax 6 and further processed in Photoshop CS5.

There are many different kinds of clouds and hazes on Mars:

• Polar Hoods are clouds or ice fog that form over the polar cap in the autumn season for their respective hemispheres. They are caused by cooling temperatures when water vapor condenses into clouds.

• Orographic Clouds form over mountains and volcanoes from Martian air being lifted over these structures and moisture condensing when the gases in the atmosphere cool due to lower pressure at higher elevations. These are frequently seen over Tharsis and Elysium. The famous W-shaped cloud that forms over Olympus Mons and other volcanoes on Tharsis are an example of orographic clouds.

• Dust Storm Clouds can cover small areas or the entire planet. Dust storms form when the Sun heats the Martian air, causing winds to blow, lifting dust from the surface. Many Martian dust storms originate in the Hellas Basin. Planet covering dust storms are, however, fairly rare on Mars, with only 10 global-wide storms reported between 1877 and 2003. Dust storms usually peak during the southern Martian summer.

• Discrete Clouds form over Libya, Chryse and Hellas regularly. Of particular interest is the Syrtis Major Blue Cloud that forms over Libya and Syrtis Major and makes the surface look blue.

• Limb Clouds are visible on both the eastern and western limbs of Mars caused by dust and carbon dioxide particles in the atmosphere scattering light. Since we are looking through the maximum amount of atmosphere on the limb, these clouds are more visible there. These clouds can also look like a blue haze on the limb. Limb clouds on the morning limb just rotating into the sunshine can be patches of fog or frost that usually dissipate during the Martian day, although sometimes the frost can last all day. Evening clouds on the opposite limb can be larger and more plentiful, getting larger as the day progresses on Mars.

The Moons of Mars

Mars's moon Deimos is visible next to a greatly overexposed image of Mars itself. A correctly exposed image of Mars is composited into the image at its correct size. Mars's other moon, Phobos, is lost in the glare from Mars because it orbits closer to the planet. The location of where it would have been is shown with a tiny black dot added next to Mars. This image was taken with a Celestron 11 Inch Edge HD f/10 Aplanatic Schmidt Cassegrain working at f/10 at 2,709 mm of focal length with a Canon EOS T2i (550D). It was shot as a single frame with 30 seconds of exposure at ISO 1600.

Mars has two moons - Phobos and Deimos. They were discovered by Asaph Hall in 1877. To go along with the mythological nomenclature of Mars, Phobos means "fear" and Deimos means "dread", appropriate companions to the God of War.

Deimos has an average diameter of about 12 km (7.5 miles), but is irregularly shaped, like an asteroid. It shines at an average magnitude of 12.45. It orbits around Mars at a distance of about 23,458 km (14,576 miles). It takes Deimos 30.2976 hours to make one orbit around Mars.

Phobos has an average diameter of about 22 km (13.6 miles). It is the brighter of the two moons, shining at magnitude 11.4. It orbits closer to Mars than Deimos however, at an average distance of only 6,000 km (3,700 miles) above the surface of the planet. It takes Phobos just 7.65 hours to orbit around Mars.

Sky & Telescope's Mars's Moons javascript utility gives the locations of Mars's moons for a given date and time.

It is difficult to photograph the moons of Mars because of the tremendous difference in brightness between them and the planet, and because Phobos orbits so close.

When the image above was taken, Mars shone at magnitude -1.2 and Deimos at magnitude 13.3. With the 14.4 magnitude difference, Mars was more than 1/2 million times brighter than Deimos. Each astronomical magnitude is brighter by a factor of 2.5119 (the fifth root of one hundred). Since the image was exposed for Deimos, Mars is tremendously overexposed. The large red circles on the sides of the image are reflections off the sensor.

Mars Global Map

Hold your mouse cursor over the image to see feature identifications on the planet. This global map of Mars was combined from four hemispheric views taken by the Hubble Space Telescope. Image credit: Steve Lee (University of Colorado), Jim Bell (Cornell University), Mike Wolff (Space Science Institute), NASA.

Tips for Photographing Mars

• The same features on the surface of Mars are visible 37 minutes later each day.

• If you want to shoot the same feature transiting the meridian at the same time each night, you will have to wait 41 days. For example, if you shoot Syrtis Major transiting at midnight, you will have to wait 41 days for it to transit at midnight again.

• Mars is largest and brightest at opposition which is usually the best time to shoot it.

• Really interesting surface details get big enough to shoot when Mars gets around 10 arcseconds in size.

• Because there can be really fine details present on the planet, excellent seeing and correct sampling are important.

• Mars is fairly bright at opposition, so your exposure will be about 1/60th of a second at ISO 400 at f/30.