Category Science

Our Planet Earth

 

 

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, except under the special conditions that you might find inside the hot core of a star. A total of 92 different elements are found in nature. Other elements can be made in laboratories, but they have only a very short life.

Minerals, which make up the solid surface of the Earth, consist mostly of combinations of elements. The minerals gold, diamond and graphite are examples of single elements, while most others contain several elements. 

 

 

 

 

 

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 when water evaporates, and substances dissolved in the water gradually grow into a crystal. Other crystals are formed under great pressure. Diamond crystals are made when carbon dissolves in molten rock deep down below the Earth’s surface. The diamond crystallizes out and is later uncovered on the surface either by volcanic action or by erosion of the Earth’s crust. Other valuable gems are formed in a similar way, and most of them contain compounds of aluminium.

 

 

 

 

 

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 by map-makers because it makes a convenient point from which to measure distances, together with the geographic North Pole and South Pole. On a map, the Equator is positioned at 0 degrees of latitude. It divides the Earth into two halves, which we call the north and south hemispheres. 

Our Planet Earth

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 is a layer of liquid rock, called the outer core, which extends about halfway to the surface. Beyond this is a thick layer of rock called the mantle, which is partly molten and runny. The thinnest layer, or crust, is on the Earth’s surface, floating on the red-hot liquid mantle. The crust is about 6 km thick under the oceans, but 30 to 40 km thick beneath the land. 

 

 

 

 

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 surrounds the Earth and extends right out into space. The Earth’s magnetic field is changing constantly. This means that the magnetic north pole is not always the same as the geographic, or true, North Pole that you find on a map, although it wanders about in the same region. Millions of years ago, the north magnetic pole lay in what is now the Sahara desert. 

 

 

 

 

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 15,000 million years ago. We can calculate the ages of the Earth and the Universe by examining meteorites, and also by looking at changes in the atomic structure of some of the elements found on the Earth. Radioactive elements decay at a steady rate, and these changes can indicate the age of the Earth and other planets, as well as the age of the stars. 

Space Travel

 

 

 

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 about life on Earth to be read by any extraterrestrial travellers who might meet the probe. 

 

 

 

 

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 more suitable for longer stays in space. Rockets or the space shuttle bring supplies of air and food to the space station, and often a new crew. Space stations are usually made up of several modules that are sent into orbit, one at a time, and assembled in space. Some space stations, such as the Russian Mir, stayed up for many years, and their crews remained in space for months at a time. 

 

Continue reading “Space Travel”

Space Travel

 

 

Rocker power!

All 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 stream out through the nozzle they provide the thrust to push the rocket up into space.

Some rockets are powered by burning kerosene or liquid hydrogen with liquid oxygen, but this requires very careful handling. Other rockets burn solid fuel in a controlled explosion.

 

 

 

One giant leap!

The Apollo project was the United States’ plan to get humans on the Moon during the 1960s. It used the world’s most powerful rocket, Saturn V, to launch the three-man Apollo spacecraft. While orbiting the Moon, the Apollo craft would separate into two parts. The landing module carried two astronauts down onto the Moon’s surface, while the main part remained in orbit with the third astronaut. 

 

 

 

 

 

 

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 is less than 200 km above the Earth, faint traces of air will gradually slow the satellite so it loses height and eventually crashes to the ground. Satellites that are much higher can stay up indefinitely. Some satellites are placed in a geostationary orbit. This means that their speed exactly matches that of the Earth’s rotation, and they seem to stay above a fixed point on the ground. 

Space Travel

 

 

Who was the first man into space?

Yuri Gagarin was the first man to orbit the Earth. On April 12, 1961 the Soviet Union launched him into space, carried by a converted intercontinental ballistic missile. He only made a single orbit of the Earth and landed safely by parachute. 

 

 

 

 

 

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 shuttle is a bulky delta-winged aircraft with powerful rocket motors. At launch, two solid-fuel booster rockets are strapped to its sides, and a giant fuel tank is fixed to its belly. The rockets and fuel tank fall away after launch, and the rockets are recovered and re-used. In orbit, the shuttle’s cargo bay opens to release satellites or allow the crew to work in space. The shuttle lands on a runway like a conventional aircraft. 

 

 

 

 

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 at them from the Earth, and send them on to other places. They transmit television and telephone signals around the world, even to remote areas. They are also used for defence communications, including checking on the movement of military forces. Satellites can survey the Earth’s surface, predict weather changes and track hurricanes. They can also help to examine resources such as crops, forests and even minerals. Navigation satellites enable people on land or at sea to work out their exact map position, to within a few metres. 

Our Moon

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, many of which are the remains of impact craters and volcanoes that were active when the Moon was still hot. There are some huge valleys called rilles, which can be hundreds of kilometres in length and look like river-beds. However, scientists do not yet fully understand their origins. 

 

 

 

 

What’s on the far side of the Moon?

The far side of the Moon was a mystery until 1959, when a Soviet space probe took the first photographs of it.

The actual appearance of the far side was something of a disappointment, because it had far fewer craters and other physical features than the familiar side that always faces the Earth.