Comet

Comet A small member of the solar system that becomes visible only when it reaches the vicinity of the Sun. It is composed of ice and dust, rather like a dirty snowball. When it nears the Sun, the pressure of the solar wind evaporates the ice and drives off the dust.

This usually produces a visible tail to the comet, pointing away from the Sun. Comets orbit the Sun and may have periods of a few years (like Encke's comet), of a few decades (like Halley's comet) or very long periods of tens of thousands of years.

Moon

Moon A Earth's only satellite and nearest neighbour in space, lying on average some 384,000 km (239,000 miles) away. With a diameter of only 3476 km (2160 miles) and a relative density of 3-3, it has a mass 1/81 that of the Earth. Its surface gravity is only one sixth that of the Earth. It is an airless and waterless world, which suffers extremes of temperature and where no life can exist.

The Moon had a captive rotation, which means that it keeps the same side facing towards us as it revolves around the Earth. Two main surface features are visible from the Earth-Dark plains called maria (seas) and rugged highland, which appear bright. The highland regions a heavily cratered. Between 1969 and 1972, 12 American Apollo astronauts explored the Moon on foot and returned with 385 kg of soil rocks and core samples that are still being analysed.

The Moon rocks are of two main types similar to basalts and breccias on Earth. They contain the same elements such as chromium, titanium and zirconium.

Equatorial mounting & Newtonian telescope

Equatorial mounting The usual method of mounting an astronomical telescope. The mounting has one axis (polar axis) pointing towards the celestial pole, and therefore parallel to the Earth's axis. The telescope is carried on another axis (the declination axis) at right-angles to the polar axis. With this mounting, the telescope can readily follow a star across the sky.

Newtonian telescope A reflecting telescope designed by Isaac Newton in 1668. The principle is still widely used. In a Newtonian reflector, the light is gathered by a parabolic mirror and reflected back up the telescope tube to a plane mirror angled at 45*. This mirror deflects the light to the side of the tube, where an eyepiece is located.

Atmosphere

A = Original atmosphere of hydrogen, methane and ammonia
B = Water added from cooling rocks
C = Carbon dioxide and sulphur dioxide added by volcanoes
D = Oxygen produced by photosynthesis

Atmosphere the layer of gases around a planet, particularly the Earth. Scientists Divide the Earth's atmosphere into several layers which, from the ground upwards, are troposphere. Among the other planets in the solar system, Venus has a thick atmosphere; Mars has a slight atmosphere; and Jupiter and the other outer planets have a very thick atmosphere.

Whereas Earth's atmosphere consists of air, those of Venus and Mars are mainly carbon dioxide; and those of the outer planets, hydrogen and helium.

Stars

Evolution Stars

Stars Huge balls of glowing gases, which give out all forms of electromagnetic radiation head, light, X-rays, radio waves, etc. The energy comes from thermonuclear (fusion) reactions taking place in the centre of the star, the main reaction being the conversion of hydrogen into helium.

The Sun is a typical medium-size star, classed as a yellow dwarf. Super giant stars are many hundreds of times bigger than the Sun, while white dwarfs are several hundred times smaller. Stars vary in mass from about 10 times the mass of the Sun.

Their surface temperatures vary from about 20,000 Celsius for red dwarfs such as Proxima Centauri. Proxima Centauri is the closest star to the Sun and is about 4 - 28 light-years away. Most information about the stars is obtained by studying the lines in their spectrum. In the heavens two out of three stars have at least one companion star. On a broader scale, star cluster together in space into galaxies.

Asteroid

Asteroid or minor planet , a small rocky body that orbits the Sun. Most Asteroids orbit in a belt between the orbits of Mars and Jupiter. The largest asteroid Ceres some 1,000 km in diameter was discovered by Giuseppe Piazzi on the first day of 1801. Over Hundreds of thousands asteroids have been identified but thousands more exist, to small to be seen from Earth.
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Solar System

Solar System : The Sun and all the bodies that circle around it in space and bound to it by gravity. They include the planet and their moons, the asteroid, the comets and the smaller lumps of rocks that burn up in the Earth's atmosphere as meteors. From one extreme of the orbit of Pluto to the order, the solar system spans a distance of some 12,000 million km

Can you remember the order of the planet?

SUN
Diameter at equator : 1,392,000 km
Time for 1 rotation : 25 days
Mass of sun : 1.99x10 (30) kg
Centre temperature : 15,000,000 kelvin
Surface temperature :5,770 kelvin

MERCURY
Diameter at equator : 4,879 km
Distance from sun : 57,900,000 km
Time for 1 rotation about axis (length of 1 day) : 59 days
Time taken to orbit sun : 88 days

VENUS
Diameter of equator : 12,104 km
Distance from sun : 108,200,000 km
Time for 1 rotation about axis (length of 1 day) : 143 days
Time taken to orbit sun : 225 days

EARTH
Diameter of equator : 12,756 km
Distance from sun : 149,600,000 km
Time for 1 rotation about axis (length of 1 day) : 23 hours 56 minutes
Time taken to orbit sun : 365 days 5 hours 48 minutes

MARS
Diameter of equator : 6,794 km
Distance from sun : 228,000,000 km
Time for 1 rotation about axis (length of 1 day) : 24 hours 37minutes
Time taken to orbit sun : 687 days


JUPITER
Diameter of equator : 142,884 km
Distance from sun : 778,400,000 km
Time for 1 rotation about axis (length of 1 day) : 9 hours 51 minutes
Time taken to orbit sun : 11 years 315 days

SATURN
Diameter of equator : 120,536 km
Distance from sun : 1,427,000,000 km
Time for 1 rotation about axis (length of 1 day) : 10 hours 14 minutes
Time taken to orbit sun : 29 years 167 days

URANUS
Diameter of equator : 51,118 km
Distance from sun : 2,869,000,000 km
Time for 1 rotation about axis (length of 1 day) : 17 hours 18 minutes
Time taken to orbit sun : 48 years 6 days

NEPTUNE
Diameter of equator : 50,538 km
Distance from sun : 4,496,000,000 km
Time for 1 rotation about axis (length of 1 day) : 18 hours
Time taken to orbit sun : 164 years 288 days

PLUTO
Diameter of equator : 2,445 km
Distance from sun : 5,900,000,000 km
Time for 1 rotation about axis (length of 1 day) : 6 days 9 hours 17 minutes
Time taken to orbit sun : 248 years 183 days

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MOON
Distance of moon from earth : 384,400 km