Here's our moon, photgraphed by the crew of Apollo 11. The Apollo 11 mission in July 1969, with Neil Armstrong, Edward Eldrin and Michael Collins, was the first that landed on the moon.

The moon is, on average, 380 000 km away. The Earth is 81 times heavier than the Moon, but even so the Moon is large, as far as planetary satellites go. It's composition is very different from that of The Earth, implying that when The EArth and Moon formed, they were much fiurther apart (?)

It's orbit is 'locked' in that the same side of the moon always faces the Earth. This is a result of tidal forces between the Earth and moon. These forces try to elongate the Earth and moon and are responsible for causing the sea level on Earht to rise and fall twice daily. There are several large dark areas on The Moon known as mare or seas. Most of the seas happen to be on the side which faces us, making up what looks like a face.

Here's a photo of our planet over the moon's horizon, taken from the command module on the Apollo 10 mission earlier in 1969.

    The planet Mercury. This is a photographic mosiac made up from images from Mariner 10, the only probe ever to have visited the planet.

    Mercury lies 45 million km from the Sun. Although it looks grey in the picture, it looks somewhat orange when viewed through a telescope. It is a heavily cratered world but lacks the seas that are seen on the moon. It's diameter is just 4878 km. It's orbital period is 88 Earth days and it's rotational period is 59 Earth days. Consequently the period between succesive sunrises is 176 Earth days. The sunlit side of the planet can reach temperatures of 350°C. The dark side, however is cold, as there is no atmosphere to retain the heat. There might be ice inside some of the craters near the poles where there is never any direct sunlight. It might be as cold as -220°C there.
     The planet's orbit is somewhat eccentric. The axis of the orbit precesses at a rate of 4 arcseconds per century. This precession is a result not of classical mechanis but of general relativity, The planet has relatively large iron core and thus a strong magnetic field for it's size, though the Earth's is 100 times stronger.

The planet Venus, another image from Mariner 10.

A beautiful looking cloudy planet, and the brightest object in the sky other than sun and moon. The world beneath the clouds is not accommodating. The surface temperature can reach 480°C and the pressure is about 9 times that on Earth. It is the atmosphere of carbon dioxide that gives rise to these temperatures (greenhouse effect run riot). The planet's surface was accurately mapped in 1990 by the Magellan probe. The age of the surface (inferred from the density of craters) appears to be the same all around the globe, implying that every so often the planet is plagued is plagued by volcanic activity.

Venus is unique amoung the planets in that it rotates in the opposite sense to all the other planets. It has no magnetic field.

The Planet Mars, taken with the Hubble Space Telescope (HST)

This is the red planet with the thin carbon dioxide atmosphere that we are thinking of sending astronauts to. With a surface gravity one third that of Earth, temperatures always below 0° and no protection from ultra-violet radiation (i.e. no ozone layer) the long-term habitation of Mars by humans is a challenge, but not an impossible one, many think.

The northern polar ice cap is visible in this image, which is made of water and carbon dioxide ice. The solar system's largest volcano, Olympus Mons, is found on Mars, though inactive. It is 25 km high and 600 km wide at the base.

It was once believed, from early telescopic observations, that there were canals on the planet's surface. This is not the case, but there are scientists who believe that there is a good chance that life exists on Mars, possibly under the surface, or that there may have life there. Certainly asteroids have been found that have traces of amino acid. Some even believe that life on Earth may have originated from Mars.

Here on the Martian surface, is the Pathfinder.

I always find it difficukt to believe, when looking at photos of the Martian surface, that it is real!

The pathfincder was the first probe to land on Mars. The first was Viking 1 in June 1976 and the second Viking 2 inSeptember that year. The pathfinder landed in July 1997.

Here's a Voyager 1 photograph of Jupiter, the largest planet in the solar system with an equitorial diameter of 144000km. It weighs twice as much as the other planets put together. The great red spot is a meterological feature. Other spots appear and disappear rapidly, but this one has survived for over 200 years. Jupiter spins on it's axis in 9 hours and 50 minutes and is the fastest spinning planet.

The planet's outer layers are composed mainly of gaseuos hydrogen and also helium, ammonia and water. The planet generates a lot of heat internally and the central temperature may be as high as 30000 ºC. It is believed that at the high central pressure hydrogen becomes metallic. Jupiter has a very powerful magnetic field and close to its equator are tense radiation zones.

Here's the biggest scar that was left behind when the comet Shoemaccher-Levy 9 collided with Jupiter on July 1994.

This image was taken with the HST.

Here's Io, Jupiter's innermost moon, easily visible with a small telescope. It is plagued by volacnic activity and the yellow colour is due to sulphur. The volcanism is probably sue to the intense tidal forces from Jupiter. It lies within Jupiter's intense radiation zones, making it a somewhat inhospitable world.

The next moon out, Europa has a very smoth surface. We believe that the surface is made up of water ice over a subterraean ocean. An excellent place for ice-skating.

The other two large moons of Jupiter are Ganymede and Callisto. Ganymede is the largest sattelite in the solar system and is larger than the planet Mercury.

Here's a Voyager 1 photograph of the planet Saturn. Its avaerage distnce from the Sun is 1400 million km as is the most distant planet visible to the naked eye. The planet's diameter is 120500 km at the equator but only 109000 km from pole to pole. This descrepancy is due to the fast rotation speed of 10 hours and 14 minutes and is thus the leastr spherical of all the planets. It's famous for its extensive ring system, whose overall diameter is about 270 000 km. The ring system is only a few 10s of meters thick, and so are almost invisible if viewed edge on. The voyager crafts showed that the rings are made up thousands of ringlets. In the photogrph the Cassini and Encke divisions are obvious, bit there are ringlets within those divisions as well.

Saturn has large number of moons. Some of them seem to be respnsible for holding the rings together and are called Sheperd moons. The most interesting moon is Titan. It is 5km in diameter and has an atmosphere. It is a thick atmophere composed mainly of methane.  It has been suggested that there might oceans of methane and/or ethane. We'll soon know more about it know that the Huygens lander has made it successfully.

Here's Saturns moon Mimas, it bears a huge crater and looks like an eyeball.

Here's a Voyager 2 photo of Uranus. It was discovered in 1781 by William Herschel. It generates very little internal heat and consequently has a cloud top temperature on only 214°C and lacks the intence meterology of the other giants. It has a ring system, of nine thin rings. They were discovered in 1977 when the planet passed near a star and the star became intermitently as it passed behind the rings. Uranus is a rather uninteresting planet excpet that it's rotational axis is inclined at 82° from the ecliptic, this might have been due to a cometary impact.

Here's a Voyager 2 image of Uranus' moon, Miranda, which is a jumble of lumps of ice and rock. A mighty collision might once have broken this moon up into bits and then, through mutual gravitation intereactions, the fragments coagulated back together.

Here's a Voyager 2 photograph of Neptune. It was discovered in 1846 by Johann Galle and Heinrich D'Arrest. Naming it after the god of the sea seems apt, regarding it's colour. It's similar in volume to Uranus but is heavier. It's cloutop temeratures are similar to that of Uranus despite being very much further from the Sun, due its internal heat. The dark spot in the photograph is not there anymore.

Neptune's largest satellite, Triton, is very interesting. Over much of the surface there is frozen methane and ice, but it's southern polar cap is pink due to frozen ntirogen. There are very few craters or mountains.

Pluto, the ninth planet in the solar system, has never been imaged from close range. HST images suggest that it may have a surfcace partially covered in frozen nitrogen.

Here's the comet Hale-Bopp which made a close approach to Earth in early 1997. It will return in 3500 years.

Comets are pieces of rock with ice and frozen carbon dioxide, nitrogen and methane. They move in highly eccentric orbits round the Sun. When they come close to the Sun the ices start to evaporate to produce a bright coma and a long wispy tail. In fact there are usually more than one tail. There are ion tails and dust tails. The tails always point away from the Sun. Ion tails are straight as photon pressure from the Suns rays is pushing back the ions. Dust tails are curved and solar wind particles are pushing back the dust particles.

The origin of the comets is not definite. Bright, longh period comets, such as Hale-Bopp , are believed to have come from the Oort cloud, a band of particles that circulates the Sun at distance of roughly 1 light year.

There are also a large number of short period comets with period shoter than 50 years. The comet discovered with the shortest period is Encke's comet with a period of 3.3 years. but they probably come from the Kuiper belt, which is a band of rocky particles that circulates the Sun just beyond the orbit of Neptune. The gravitational pull of Neptune may dislodge some of these rocky particles into an elliptical orbit.