Few sights match the beauty of Saturn's ring system, although Saturn itself, the sixth planet from the sun, is almost featureless. The rings do not touch Saturn. The rings look solid, but in fact, they are made of numerous ringlets that blend together. The ringlets are made of billions of ice particles. Each particle has its own orbit around Saturn, like a moon. Due to the planet's distance from the sun (1,426,980,000 km!) the ice particles never melt. The beautiful rings of Saturn are the thinnest structure in nature when width is compared to thickness. The rings are about 1,000,000 km wide, but they are only a few tens of metres thick. Gaps between the rings are caused by the gravity of the moons.

The rings are named as follows: A, B, C, D, E, F, and G. The A ring is the outermost ring visible from Earth. The B ring is the broadest and brightest ring. The C ring is nicknamed the "Crepe ring" and is the faintest and bluest ring visible to people on Earth, looking at the night sky. The D ring is the closest ring to Saturn and is very faint. The E ring, the widest of the rings, is 600,000 km wide, but it is also very faint. The F ring, discovered by Pioneer 11 in 1979, is the outermost of the bright rings and is very narrow. The G ring is another narrow ring, beside the F ring. The Cassini Division, discovered by Italian Giovanni Cassini in 1675, between rings A and B, appears to be a gap between the rings, but it is made of at least 100 faint ringlets. No one is sure how the rings were formed, but some people think that if a moon gets too close to a planet, the planet's gravity will tear the unfortunate moon and the fragments simply orbit it. Although all the gas giants (Jupiter, Saturn, Uranus, and Neptune) have rings, Saturn will always be known as the planet with rings!

Black holes are among the weirdest things in the Universe. If a star quickly grows, then it will become very big and eventually blow itself apart in a supernova. The remains will either be a very dense neutron star, where only a part of it the size of a pinhead weighs as much as 3 Empire State Buildings, or a black hole. Whether the star will become a neutron star or a black hole depends on the star's weight. If the exploding star is more than 30 times the mass of our Sun, the remains do not stop compressing. Instead, it's own gravity crushes itself out of existence, leaving a gravity field; that is what a black hole is.

A black hole has an event horizon, where anything in it gets swallowed up and out of the Universe for good. Not even light can escape. Fortunately, the reach of the event horizon is short. But if you're one of those people who actually want to go into a black hole, don't even think about it. No one can get close to one right now. A black hole is the ultimate trash can. Anything that falls in will never get out. Black holes are also the most invisible trash cans. Since no light can escape, black holes cannot be seen. But if a star is close to a black hole, then gas will drag to the hole. Just before the gas is sucked in, it releases a burst of X-rays (so maybe strong X-ray sources are black holes).

The best candidate so far for a possible black hole is in the constellation of Cygnus, the Swan. The black hole (if there is one) weighs 10 suns and gives out X-rays, as expected. In a few million years, the black hole may have sucked in most of Cygnus X-1, its companion star.

Super-massive black holes are usually in the middle of galaxies. There may be a black hole in the centre of the Milky Way weighing as much as 4 million suns. Centaurus A galaxy, located 16 light-years away, is thought to have a black hole in its core. M87, the biggest known galaxy, is believed to have a gigantic black hole with the mass of 5 billion suns, located in its centre. In April 1991, scientists discovered a galaxy called NGC 6240, which may contain a black hole with the mass of 100 billion suns! This black hole is about as massive as half of the whole Milky Way, but only one-thirteenth the diameter.

If the sun somehow became a black hole (it never will) it would have to collapse to a radius of 3km, with an event horizon of 9 km. Since even Mercury, the Sun's closest satellite, is not that close, the planets would orbit the black hole normally, with the only side effect being darkness. The Earth would have to be squeezed to a radius of 9 mm to form a black hole.

Time slows down near a black hole, and inside it stops completely, which means nobody can see you going inside the black hole. So now do you think a black hole is the weirdest thing in the Universe? Why or why not?

Mars, the fourth planet from the sun, is also the planet that most resembles Earth. In some ways it is similar to our planet. It has mountains, deserts, polar caps, volcanoes, canyons, and dry riverbeds indicate that water once flowed on Mars. It is the only extra-terrestrial planet that scientists have considered a possible site for life. A century ago, astronomers saw "canals" crisscrossing the planet's surface. They thought that Martians had dug them to preserve their dwindling water supply. In fact, the "canals" are actually optical illusions! Billions of years ago, Mars might have had an atmosphere that could have sustained life. But over time, the atmosphere escaped into space, and Mars grew cold. Today, Mars is a freezing desert.

You can see Mars as a bright red "star" on clear nights. The color reminded the Romans of blood spilled in battle, so they named it after their god of war, Mars. In fact, Mars gets its red color from iron oxide rust in rocks and dust that cover the planet. Astronomers mistook the darker parts of Mars as vegetation because it changed shape with the seasons. These areas are actually rocks and windblown dust. The air on Mars is 100 times thinner than the air on Earth and contains dust that makes the sky orange-red during the Martian day. The sky around the Sun turns blue in the Martian sunset. Because there is so much dust, the sky glows for more than an hour after sunset. Violent storms can sometimes whip up clouds of dust, forming dust storms. The wind speed can sometimes reach 400 km/h. The Martian atmosphere is 95% carbon dioxide, which is poisonous.

Olympus Mons, the biggest and tallest volcano in the solar system is on Mars and is a shield volcano, which means is base is very wide. In fact, the base of Olympus Mons could cover England or Arizona, and its crater could swallow New York two times over! Olympus Mons is 26.4 km tall, three times taller than Mount Everest, the highest peak on Earth. It stopped erupting billions of years ago, but it was probably not a terrifying sight while it was alive. All of Mars' volcanoes are thought to be extinct by now.

Mars has a small iron core, which is probably solid, because if it were liquid, it would have a magnetic field, and there is no detectable magnetism on Mars.

Mars' two tiny moons, Phobos and Deimos, were not discovered until 1877. They were probably both asteroids Mars managed to capture from the asteroid belt. Phobos is only 28km at its widest point, while Deimos is only 14km wide, making it the smallest moon in the Solar System. Deimos is also made of extremely dark rock, with fewer craters than Phobos and a smoother surface. Phobos orbits 9380km from Mars, while Deimos orbits from a distance of 23460km from Mars. Phobos only takes 40 min to orbit Mars while Deimos takes 30 hours. Phobos should collide with Mars in 50 million years' time, due to gravity.

Astronomers have always wanted to send people to Mars, but so far only space probes have visited our neighboring planet. The first mission to the surface of Mars took place in 1976, when two Viking landers, the most sophisticated probes to be sent to another planet, made a successful landing after an year-long trip on two specially chosen locations. The Viking landers both had a robotic arm for scooping soil and an onboard laboratory analyzed the soil for organic chemicals that living organisms produce. But neither lander found evidence of life on Mars. The landers also beamed back the first pictures of Mars' surface. They revealed a dusty, rock-strewn landscape and orange sky. The Viking landers took about 4,500 pictures of Mars' surface. They also studied how the Martian weather changes with the seasons. Viking 1 continued to operate for more than 6 years. Pathfinder, another space probe, landed more recently, on a bouncing air bag. It bounced 15 times before it stopped. Pathfinder landed close to two hills, nicknamed Twin Peaks. They proved to be an important landmark, enabling scientists to work out Pathfinder's exact location. The hills were only 1km away, but they were still too far away for Pathfinder's rover vehicle, Sojourner, to reach. Sojourner, about the size of a microwave oven, explored the area around the landing spot of Pathfinder. Its six wheels could move up or down separately to move over rocks. Scientists on Earth used the camera on Pathfinder to monitor Sojourner's movements. But the rover could also use its own cameras to find its way. Do you think that there was once life on Mars? Why or why not?

Bond, Peter.  The Firefly Guide to Space:A Photographic Journey Through the Universe. Firefly Books Ltd.,(c) 1999.
Couper, Heather and Henbest, Nigel.  The Space Altas. Dorling Kindersley Ltd.,(c) 1992.
Dixon, Sarah.  Map & Maze Puzzles. Usborne Publishing Ltd.,(c) 1993.
Mitton, Simon and Jacqueline.  Astronomy. Young Oxford Books.,(c) 1994.