Press Release

Mars in Opposition: One for the Record Books

By SpaceRef Editor
August 4, 2003
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Mars in Opposition: One for the Record Books
mars

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?

WHEN AND WHERE TO SEE MARS

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.

BRIGHTER THAN THE STARS

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.

THE CLOSEST OF CLOSE ENCOUNTERS

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’.

TAKING A CLOSER LOOK

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.

NOTES FOR EDITORS:

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.

MEMORABLE MARS MINUTIAE

* 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.

SpaceRef staff editor.