Mars in Opposition: One for the Record Books

Press Release From: Royal Astronomical Society
Posted: Monday, August 4, 2003

image On 27th August, Mars will be at its closest to Earth for almost 60,000 years. On that date, the Red Planet will approach to within 34,646,418 miles (55,758,006 km) -- 145 times the distance of the Moon.

The last time the two planets were so close our ancestors were living in caves and struggling to survive the extreme conditions of the Ice Age. Who knows what will have happened by the time they are as near again -- 284 years into the future?


Mars is now in the constellation Aquarius and is readily recognised because it is already the brightest object in the night sky (apart from the Moon). Instantly recognisable by its brilliance and orange-red colour, it will remain easy to spot for several months, low in the sky somewhere between the southeast and the southwest. (Exactly where depends on the date and time.)

Currently, Mars rises at about 11 pm (BST) but it comes up a few minutes earlier each night. Future rising times are 10 pm on 7 August, 9 pm on 21 August and 8 pm on 4 September. About 5 hours after it has risen, Mars reaches its highest point above the horizon -- an altitude of about 23 degrees as seen from London -- and lies due south.


At its peak brightness, Mars will reach magnitude -2.9, far outshining the brightest star, Sirius (magnitude -1.5). It will remain brighter than Sirius until mid-October. Venus is the only planet that can appear brighter, but Venus will not be visible again until December.


Earth and Mars are rather like two runners going around a racetrack in lanes at different speeds. Mars travels around the Sun about one and a half times farther away than Earth on average and takes 687 days to make a circuit compared with Earth's 365 days. Roughly every 26 months, Earth overtakes Mars on the inside. When this happens, there's a close encounter between Earth and Mars and the two planets line up in space with the Sun. This orbital rendezvous is called an OPPOSITION of Mars, because the Sun and Mars are on opposite sides of Earth.

If the orbits of Earth and Mars were circles, Mars would be the same distance from Earth at every opposition. But the orbits are actually ellipses (oval-shaped), with the Sun offset from the centre. Mars, more so than Earth, follows a very non-circular orbit, so its distance from the Sun varies by 26.5 million miles (42.4 million km). This means that the distance between Earth and Mars at an opposition can be anything between about 35 million miles (56 million km) and 63 million miles (100 million km).

Because Mars's orbit is so elliptical, the time when Mars and Earth are closest and the actual opposition -- when Sun, Earth and Mars are in a direct line -- do not quite coincide. This year's opposition is on 28 August, a day later than closest approach.

Every 15 - 17 years, there is an opposition of Mars when the Red Planet is not far from its closest point to the Sun -- its 'perihelion'.


Mars is a small planet, roughly half the size of Earth. At its closest, it appears little more than half the size of Jupiter, or similar in size to a large crater on the Moon.

To see markings on its surface, you ideally need at least a 6 inch (15 cm) telescope. With a magnification of 40 when at its closest, Mars would appear about the same size as an orange seen with the naked eye across the length of a tennis court. You could see it was an orange but that's about all -- it would be quite small.

To see any markings and the famous polar ice caps, a higher magnification is needed, if the telescope is good enough. Unfortunately, detailed observing will not be very easy from the UK at this opposition because Mars is so low in the sky.

It is now spring in Mars's southern hemisphere and the ice cap at the south pole is tilted towards Earth. As the atmosphere warms and the thin air begins to stir, dust storms frequently occur. Huge storms can sometimes shroud large areas of the planet, hiding the giant volcanoes and other surface features.


On 27th August at 10:51 BST (9:51 GMT) Mars will be closer to Earth than at any time since the year 57,617 BC -- 59,619 years ago. It won't be as near again until 28th August 2287.

However, it is not too unusual for Mars to come almost as close. In 1924, for example, it was only 12,500 miles (20,000 km) farther away and to ordinary observers the planet looked just the same as it will this year.

UK National Astronomy Week 2003 (23 - 30 August) has been selected to reflect the time when Mars will be at its closest to Earth and when public interest will be at its highest. During that week, Mars will rise at about 9 pm BST and will be high enough to observe reasonably well by about 10:30 pm, about 11 deg above the horizon. This may not be the ideal time to observe it, as it will mean a late night for many people, and it will be higher in the sky later in the year, but this is the time most people will want to see it and the media attention will be at its peak.


* In Assyria, Mars was known as the "Shedder of Blood". The Red Planet also represented the god of war for the Vikings, the Greeks and the Romans.

* The red colouration of Mars is due to oxidised iron minerals in the surface rocks -- rust.

* Mars is considerably smaller and less massive than Earth so its surface gravity is only one third of that on our planet. An astronaut weighing 60 kg on Earth would only weigh 20 kg on Mars.

* The surface area of Mars is approximately the same as the land area of Earth.

* A Martian day (known as a 'sol') lasts for 24 hours 37 minutes -- only a little longer than a day on Earth.

* After Italian astronomer Giovanni Schiaparelli announced the discovery of "canali" (channels) on Mars in 1877, there was intense speculation that intelligent life existed on the planet. Their existence was not disproved until the first spacecraft visited Mars in the early 1960s.

* An Orson Welles radio presentation of The War of the Worlds, broadcast in 1938, caused widespread panic in America when listeners believed that a Martian invasion had begun.

* Mars approaches closer to Earth than any of the other planets apart from Venus.

* The air pressure on Mars is less than 1% of that on Earth -- equivalent to the air pressure at an altitude of 30 km above the Earth's surface. As a result, liquid water immediately sublimates (changes to a gas) on reaching the surface.

* The polar caps of Mars contain both water ice and dry ice (frozen carbon dioxide).

* Mars has two small moons: Phobos (fear) and Deimos (panic), which are thought to be captured asteroids. Although they were discovered by American astronomer Asaph Hall in 1877, they were 'predicted' 150 years earlier in Swift's novel Gulliver's Travels.

* Unlike Earth's Moon, Phobos and Deimos are too small to completely block the Sun when they pass in front of it, but they do cast a shadow over the Martian surface.

* Two NASA orbiters (Mars Global Surveyor and Mars Odyssey) are currently mapping Mars. Five more spacecraft are en route to the Red Planet: the Mars Express orbiter (the European Space Agency's first planetary mission), the British-led Beagle 2 lander (the first UK-built spacecraft to land on another world), the Nozomi orbiter (Japan's first planetary probe), and two NASA rovers (Spirit and Opportunity).

* NASA's Mars Pathfinder rover mission, which landed on 4 July 1997, was one of the most popular events in Internet history. A total of 566 million "hits" was registered on NASA's Pathfinder Web sites during the first month on Mars, with 47 million hits on 8 July alone.

* Scientists have found over 20 meteorites that have come from Mars. They seem to have been blasted out of Mars by large asteroid impacts, then spent millions of years travelling through space before they landed on Earth. Some scientists claim that they have found evidence of primitive microbial life in several of these meteorites.

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