What is the continental shelf?

The shallow underwater plateaus of land surrounding the continents form the continental shelf. They slope gently down to a depth of about 180 m, after which they slope more sharply...

What causes the tides?

Tides are caused by the gravity of the Moon. As the Earth spins round, the water in the oceans is 'pulled' towards the Moon slightly, making a bulge. There is a corresponding bulge...

What causes waves?

A combination of wind and the shape of the sea-bed causes waves. Wind blows the surface layers of the sea, gradually forming a rolling movement of waves. As these waves near the...

What are the northern lights?

The northern lights are streaks and sheets of pale, flickering, colored lights that are sometimes seen in the night sky in far northern regions. Their proper name is the aurora...

Why are times different in other countries?

Clocks in other countries need to be adjusted so that it gets light and dark at approximately the same time everywhere. Without this adjustment, people might find that dawn was at 10...

Why do we have day and night?

As the Earth spins on its axis, the Sun always shines on one side giving us daylight. It is night on the shaded side. As the Earth continues to turn, the shaded side moves into...

How much of the Earth is covered by water?

More than two-thirds of the Earth's surface is covered by seas and oceans. About 72 percent of the Earth's surface is water. This water is either in the oceans, locked away as ice...

What are metals?

Metals are one of the major groups of elements. Most of them are shiny and hard. Mercury is the only metal that is a liquid at normal temperatures. Most metals can be bent and stretched...

What is the Equator?

The Equator is an imaginary line drawn around the outside of the Earth. It lies midway between the North Pole and the South Pole, at the Earth's broadest point. The Equator was invented...

Make it crystal clear!

It is easy to grow your own crystals. Take a glass jar containing hot water, and stir into it either table salt or sugar. Keep adding more salt or sugar and stirring until no more will...

What are crystals?

Crystals are solid substances that are naturally formed into regular geometric, angular shapes. All crystals can be classified into seven systems. Sometimes a crystal is formed...

What is the Earth made of?

The Earth is made up of elements. These are the simplest possible substances, which are composed of one kind of atom. Elements cannot normally be broken down into other substances,...

How old is our Earth?

The Earth is thought to be about 4,600 million years old. The oldest rocks so far discovered are up to 3,800 million years old. The Universe is much older, and probably began about...

Why is the Earth like a magnet?

The Earth acts as if it is a huge magnet. When the solid rocky core moves inside the liquid rock above it, it creates a magnetic field with a north pole and a south pole. This field...

What is inside the Earth?

The Earth is not solid rock all the way through. It has an inner core of solid rock, which is mostly iron. The temperature here is probably around 4,500°C. Beyond the inner core...

How do you breathe in space?

You cannot breathe in the vacuum of space because there is no air. Oxygen is the gas we need to stay alive, and it forms an important part of the air we breathe. AII space missions...

What is a space station?

Space stations allow the crew to work in space for long periods in conditions of zero gravity. While conditions in space capsules and the space shuttle are cramped, space stations are...

Has any spacecraft ever left the Solar System?

Pioneer 10 is the first man-made object to leave the Solar System. This probe was launched towards Jupiter in 1972 and by 1983 it had reached deep space. Pioneer 10 carried messages...

How do satellites stay up?

The speed with which a satellite is launched helps to keep it in orbit. To stay up above the Earth, a satellite must be launched at a speed of about 8 km per second. If the orbit...

One giant leap!

The Apollo project was the United States' plan to get humans on the Moon during the I960s. It used the world's most powerful rocket, Saturn V, to launch the three-man Apollo spacecraft....

Rocket power!

AII space flight depends on the use of rockets that burn huge amounts of fuel. They burn high-energy fuel in a chamber which directs the burning gases through a nozzle. As the gases...

What do space satellites do?

Space satellites have revolutionized Communications, making possible everyday developments such as mobile phones and television. Communications satellites receive signals beamed...

What is the space shuttle?

The space shuttle is the first re-usable spacecraft. It was developed to provide a re-usable, and therefore cheaper, vehicle for launching satellites and for other work in space. The...

What does the surface of the Moon look like?

The Moon's surface is covered with a thick layer of gravel-like rock and dust. This material was created by the impact of millions of meteorites. The Moon also has mountain ranges,...