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Lumps of Rock, Gas and Ice
[Mercury] [Venus] [Earth] [Mars] [Asteroids] [Jupiter] [Saturn] [Uranus] [Neptune] [Pluto]
Orbiting the Sun there are nine known (but there may be more) major planets: Mercury, Venus, Earth and Mars are relatively small and rocky, followed by Jupiter, Saturn, Uranus and Neptune which are much larger and gaseous. Tagged onto the end is the tiny frozen semi-planetary world Pluto. They're all quite a varied bunch as we shall see. There are lots of ways to remember them, but the saying I always hear is, My Very Easy Method Just Speeds Up Naming Planets, where the first letters of each word are are the first letters of each planet. However I've also heard, 'My Very Elderly Mother Just Sips Unrefined Nettle Pulp'! Charming. Use whatever work for you.
Diameter: 4,878 kilometres OBSERVING MERCURY: Mercury is quite a small planet and the word 'elusive' is often used in terms of trying to find it. This is because it stays close to the Sun and so it never appears far above the horizon. Even some astronomers have not seen Mercury!, but if you know where and exactly when to look, Mercury can be fairly easily found. A small telescope will show the phases, but not any details on Mercury's scorching surface. Due to it's tilted orbit the best times to see Mercury are the evening skies of spring or the morning skies during autumn.
Diameter:
12,104 kilometres OBSERVING VENUS: Venus is the brightest object in the sky after the Sun and Moon. Sometimes this means it can even be seen in full daylight while at night it can cast shadows. The surface is permanently covered in cloud so there's very little for your telescope to have a look at, although you can see the phases (just like the Moon) and maybe the odd wispy markings of the changing atmosphere.
Diameter:
12,756 kilometres OBSERVING EARTH: Look up, look down, look all around, and wonder.
On January 4th 2004 NASA's Mars Rover 'Spirit' continued an Earth invasion of the red planet that successfully started with the Viking landers back in 1976. 'Spirit' and its twin 'Opportunity' (landing at the end of January 2004) are looking for evidence of water and collecting data for future manned missions. We will be going to Mars. Diameter: 6,787 kilometres OBSERVING MARS: Mars can approach the Earth as close as 56 million km or as far away as 400 million km. When closest it is a fine sight in a small telescope, you may see one of the polar caps and dark markings across the planet. During these closer times Mars can also become the second brightest planet in the sky (after Venus). Telescopes gazed at Mars during the summer of 2003 because the planet had not been so close to us for almost 60,000 years!
Ceres is the largest, measuring 940 km (584 miles)
in diameter, and was also the first to be discovered in 1801. Then came
Pallas, Juno and the brightest asteroid, Vesta. Several of these minor
planets have quite down to Earth names including Hilda, Albert and Thora.
Some are even named after rock stars, such as Enya, (Eric) Clapton and
(Frank) Zappa.
OBSERVING ASTEROIDS: A few of these tiny worlds are quite easy to see with binoculars as tiny points of light. Over a few nights their movements are obvious against the background of fixed stars. There's even one that you can see with the unaided eye, that bright rock Vesta, mentioned above.
Diameter:
142,800 kilometres OBSERVING JUPITER: You'll need a telescope to see details in the atmosphere including the Great Red Spot, but simple binoculars will show up to 4 tiny dots that are the main Jovian moons. These were seen by Galileo in 1610, and so are known as the Galilean satellites. In order of distance, starting with the closest, they are Io, Europa, Ganymede and Callisto. As these moons orbit Jupiter quite fast you can watch them change position over the course of just a few hours.
The rings themselves are made up of particles of icy rock from as small as a grain of sand up to the size of a house, each individually orbiting like tiny moons. Diameter: 120,000
kilometres OBSERVING SATURN: A small telescope will reveal the rings, binoculars are just not powerful enough to get that great view. In fact, many astronomers believe Saturn to be the best thing to see through a telescope. You have been told.
Diameter:
51,118 kilometres OBSERVING URANUS: is just visible to the unaided eye in dark clear skies. Good binoculars, however, or a small telescope will show it as a small greenish-blue disk.
Diameter:
49,528 kilometres OBSERVING NEPTUNE: Due to the large distance from the Sun this is quite a faint planet only visible with a telescope.
Diameter:
2,320 kilometres OBSERVING PLUTO: Pluto is so faint that only larger telescopes will be able to find it.
PLANET X - In October
1999 it was announced a large object may well have been located (not
visually) in the depths of the solar system due its gravitation effects
on comets. Calculations show the planet, if that is what it is, must
be larger than Jupiter, sitting in the frozen depths around 35,000 times
further away from the Sun than the Earth. At this distance a year on
Planet X would last nearly 6 million years; this being the length of
time it takes to orbit the Sun once.
Edgeworth-Kuiper Belt
- orbiting beyond Pluto astronomers have found a growing collection
of tiny icy bodies (totalling 85 as of Feb 99), much like the Asteroid
Belt between Mars and Jupiter but in deep-freeze. One object in this
area is called enigmatically 1996 TL66. This 480 kilometres across object
has an orbit which brings it between Neptune and Pluto before plunging
into the depths of the solar-system on an 800 year round-trip. There
are probably thousands of similar lumps in these far-flung dark reaches
of the solar-system.
Images courtesy NASA/JPL/AURA/STScI
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MERCURY
- is the closest planet to the Sun and so is also the fastest moving
(that gravity!), orbiting our star four times faster than the Earth.
Because it is so close to the Sun the intense heat doesn't allow any
atmosphere to exist, so the daytime temperatures can reach 400°C whilst
at night the thermometer plunges to -170°C.
VENUS
- orbits the Sun in a shorter time than it rotates, meaning one Venusian
day is longer than it's year! It also comes closer to the Earth than
any other planet at 40¼ million kilometres, or just 100 times further
than our Moon.
EARTH
- Our planet orbits at a distance from the Sun that would take you 2,123
years to walk or 193 years if you were driving at 55 mph. We have one
natural satellite, the Moon, which is very slowly spiralling away from
us at a rate of 1½ kilometres (approx. 1 mile) every 28,000 years. This
means that it will appear smaller in the future to the point where total
solar eclipses will no longer occur as the Moon will not be large enough
to cover the Sun's disk. A sad day indeed. 78 per cent of our atmosphere
is the gas nitrogen, with oxygen making up 21 per cent.
MARS
- has been an endless source of fascination due to its striking red
colour, astronomers drawings of canals on the surface, HG Wells' War
of the Worlds, and more recently the search for the 'lost' oceans of
Mars. Some years ago there was a the much reported meteorite find in
Antarctica which came from Mars carrying fossilised bacteria. Many reports
since then, however, have cast doubt on so called 'evidence' of Martian
life. All in all we're not having much luck with either water or life
on the Red Planet - time will possible reveal the true Martian story.
Mars has a thin atmosphere with winds that pick up the red rusty Martian
dust carrying it like sand storms across the planet.
The ASTEROIDS
- Between the orbits of Mars and Jupiter are a collection of rocks known
collectively as the Minor Planets or the Main Asteroid Belt. One theory
about their origins is that a planet was unable to form in the area
because of the huge gravitational influence of nearby Jupiter. This
left the orbit strewn with these lumps of rock.
JUPITER
- is the largest planet in the solar system and the best to observe;
you can see the cloud belts which are blown by huge winds caused by
the very fast 10 hour rotation of the planet. Jupiter also has the famous
Great Red Spot, a storm that has raged for over 300 years. It is so
big you could fit two Earths inside it.
SATURN
- is the second largest planet and famed for its rings. It happens to
be extremely light due to its gaseous make-up and if you could find
a large enough bath, and a good supply of water, you would find that
Saturn would float!
URANUS
- was the first planet to be discovered by using a telescope (though
loads of people saw it beforehand, nobody realised what it was). Therefore
the honour goes to William Herschel on 13th March 1781. He originally
named this new world 'Georgium Sidus' in honour of King George III,
but Uranus was eventually adopted due it being more classical. The most
unusual aspect of this planet is that its axis is tilted so much that
Uranus appears to spin on its side, similar to the way a ball rolls
along the ground.
NEPTUNE
- is the last and smallest of the four gas-ball giants. Nevertheless,
it's still 54 times bigger than the Earth. It's vast distance from the
Sun means Neptune is quite faint. So it shouldn't comke as any surprise
to learn that this cold and dark world was not identified until 1846,
although Galileo may have seen it in 1612. At times it can be the furthest
main planet due to the unusual orbit of the dark and cold world, Pluto.
PLUTO
- was named after the god of the underworld because of its tremendous
distance from the Sun. This is the smallest of all the planets, smaller
than our Moon in fact, and together with its remoteness was why it wasn't
discovered until 1930. Pluto takes 248½ years to go round the Sun in
a highly eccentric orbit which brings it inside the orbit of Neptune
for 20 years of its circuit (the most recent was 1979 to 1999).
