COMETS

Comets are small balls of ice that circle the sun but their orbits are far from round. During part of a comet’s orbit, it comes very close to the sun. During another part, it is further from the sun than Pluto. Every once in a while a comet will come close enough to Earth so that it can be seen in the night sky.

Comets reflect sunlight well and are known for their long bright tails. The tails are made up of dust and gas. Because they reflect light so well, they can only be seen when they are close to the sun. During the outer part of their orbits, they are invisible.

The most famous comet is Halley’s Comet, which passes close to Earth every 72 years. In ancient times, an appearance of a comet in the night sky frightened people, who feared it meant the end of the world.

ASTEROIDS

Asteroids are small planetary bodies that revolve around the sun. Asteroids reflect the light emitted from the sun, and are therefore star-like, shiny objects. Most asteroids are in an asteroid belt thlocated between the planets Mars and Jupiter.

Some scientists feel that there might once have been a planet along that belt. They think the planet might have exploded, and the pieces of planet are now asteroids.

Others feel that the asteroids have always been asteroids. These scientists believe the asteroids are material left over from the birth of our solar system.

Asteroids vary greatly in size. Some are the size of small boulders. The largest asteroid is 600 miles across. This asteroid could be considered a minor planet. It is named Ceres.

Sun

The sun is the solar system’s most important part. It supplies all of our light and heat. Its gravity holds the solar system together. If you could put our entire solar system on a huge scale, you’d find that 98% of all the weight comes from the sun. More than one million Earths could fit inside the sun.

The part of the sun that we can see is called the photosphere. The temperature there is 11 000 degrees Fahrenheit. That seems very hot, but it is nothing compared to the 27 million degree temperature at the sun’s core. The core is the center of the sun. The sun’s outer atmosphere is called the corona.

Scientists estimate that the sun has been around for 4.6 billion years, and should be around for about another 5 billion years.

STARS

Stars are huge balls of super hot gas that produce light and other forms of energy. The sun is a star and it gives the Earth light and heat energy. Stars come in different sizes, weights, and temperature. A star’s color is determined by its temperature. The hottest stars are blue in color and the coolest stars are red. A red star can reach temperatures of about 5 800 degrees Fahrenheit while a blue star can reach temperatures of about 50 000 degrees Fahrenheit!

Did You Know??? Stars do not twinkle. Starlight enters the Earth’s atmosphere as constant, straight rays. However, because of air currents the starlight seems to blend or twinkle.

GALAXIES

Galaxies are groups of stars and nebulae. Around 100 years ago, astronomers thought that the universe was only as big as the Milky Way.

Galaxies vary in size. Some contain several million stars, and some contain even trillions! There are so many known galaxies that not all of them have names, only numbers.

Galaxies, when viewed through a telescope, can be beautiful. They come in all of the colors of the rainbow and float through space in fantastic, sometimes familiar shapes. They are truly worthy of being called heavenly bodies.

A Near Neighbour??? The Andromeda Galaxy, our “near neighbour”, is so far away that its light takes two million years to reach us!

NEBULAE

Ever wondered where stars are made? Well, now you are about to find out!

The space between stars is filled with very thin hydrogen gas and dust. A nebula (plural: nebulae) is a cloud of gas that often gathers itself together into a ball and forms a star. You could say that a nebula is a star embryo, or a future star.

New nebulae are still forming today, whenever a star explodes into a supernova.

The word nebula comes from the Latin word for cloud.

METEORS

Meteors are bits of rock and ice from out in space that get sucked into the gravity of the Earth and fall through our atmosphere to the ground.

Meteors look like “shooting stars” as they fall because when they hit Earth's atmosphere the friction of the rock rubbing against the atmosphere causes heat and light, like a fire. This heat melts all the ice off the meteor.

Most meteors are tiny, the size of pebbles, and most of them fall into the ocean, because more of the Earth is ocean than there is land. Even if they fall on land, these tiny meteors don't do any harm. Sometimes, though, much larger meteors do fall to Earth.

METEORITES

A meteorite is a massive rock and/or metal that made its way to the surface of the Earth. Before it was a meteorite, it was part of a meteor that did not totally burn up in the atmosphere.

From studying these rocks, scientists have learned a lot about the age and birth of the Solar System. Some meteorites have been proved to come from the Moon or Mars.

Did You Know??? Every day about 50 tonnes of rocky material from space lands on the Earth's surface. No one is known to have been killed by a falling meteorite, but several people have been bruised. Meteorites have also been known to kill a cow and damage houses and cars.

MOONNATURAL SATELITE

The Moon is a round, rocky ball that goes around the Earth in a circle that’s called an orbit. The moon is about ¼ the size of the Earth. It is made of pale rocks. The rocks reflect light from the sun.

All parts of the Moon are lit in turn by the Sun. As it rotates round the Earth we see different fractions of the sunlit half, or hemisphere, of the Moon. These are known as the phases of the Moon, or lunar phases. The Moon changes from a thin crescent to a full moon and back again to a crescent in one month (actually 29 days, which is a lunar month).

ARTIFICAL SATELITES

Artificial satellites are man-made and put into space to feed information directly to people back on Earth. Humans control the satellites and can choose the type of information retrieved from them.

Artificial satellites reflect the light of the Sun. So in the hour after sunset or before sunrise, the satellite is still up in the sunlight, and we can see them. Once the satellite passes into the Earth's shadow, they disappear.