Investigating space

 

A nebula is an interstellar cloud of dust and gases

What is space?

Space is emptiness. It is black because it has no light of its own. It is neither hot nor cold and there is no air or water in space. But there are billions and billions of stars, huge clouds of dust and gas, and meteorites and rocks hurtling through space. Waves of light from stars travel through it and tiny invisible particles move about in it.

Waves from space

Space is full of waves. These are waves of radiation. Radiation is streams of tiny, tiny bits of atoms travelling at tremendous speed. Radiation is given off by most things in space: stars, quasars, planets, and nebulae. Radiation comes to the Earth in the form of heat, light, radio waves, X-rays, cosmic rays, and gamma rays. The Earth's atmosphere shuts out some of these things, otherwise they could be very harmful for all living things on Earth.

How the universe was formed

Scientists have suggested various theories to explain how the universe was formed.

The Big Bang theory

This theory suggests that the universe began about 10,000 million years ago with an enormous explosion. Scientists believe that all the matter now in the universe was contained in one primitive atom which they called a primordial atom. This atom blew up and its contents flew off in all directions. As the primordial material spread out, it cooled, joined together and made the galaxies. This theory, however, does not suggest where the primordial atom came from in the first place.

The pulsating universe theory

This theory suggests that the universe is continually contracting and expanding. When the universe has expanded to a certain size, it will begin to shrink. The galaxies will be pushed closer and closer together. Eventually they will explode, causing the universe to expand again.

The expanding universe theory

This theory suggests that the universe will never collapse. It will keep on expanding. This theory implies that there has only ever been one 'big bang'.

Stars

All stars are balls of hot, glowing gas, like our Sun. But stars can be very different from one another. A star such as our Sun, is a medium-sized star. Stars called giant stars may be a hundred times bigger than the Sun. Stars called super giants may be a thousand times bigger. The smallest stars are called dwarf stars. Some of them are smaller than our Earth. The colour of a star shows how hot it is. The hottest stars shine with brilliant blue light. White stars are less hot. Yellow stars, such as our Sun, are cooler, while the red stars are the coolest of all.

Constellations

If we look up at the sky on a clear, moonless night, we will see thousands of stars. If we gaze for a while, we might be able to see some bright stars which join up to make patterns in the sky. These patterns of stars are called constellations. Ancient stargazers gave the constellations names to fit their shapes.

Galaxies

On a clear summer night, we can sometimes see a bright haze in a part of the sky. This haze is what we call the Milky Way. It looks like a gigantic cloud of stars, close together. The Milky Way is part of an even bigger cloud of stars. This star cloud is shaped like a disc with a bulge in the centre. This huge mass of stars is called a galaxy-the Milky Way Galaxy. 

Our Sun is one of the stars in this galaxy. Just as the planets move around the Sun, the Sun and other stars move around the centre of the galaxy. But, the galaxy is so enormous, and the Sun is so far from the centre, that it takes the Sun 200 million years to go all the way round it.

There are, at least, ten billion other galaxies–if not more! And each of them contains many billions of stars!

Galaxies shaped like the Milky Way galaxy are called spiral galaxies. Some galaxies are round or oval. They are called elliptical galaxies. Others have no regular shape.

Most galaxies are so far away that we cannot see them without a telescope, but we can see a few. People north of the Equator can see the Andromeda Galaxy, which is the farthest object that we can see with the naked eye. People south of the Equator can see two galaxies as white patches in the sky. They are the Small and Large Magellanic Clouds.

Strange things in space

Pulsars

Pulsars were once giant stars, but now they have shrunk so much that they appear smaller than the Earth. There is as much material in a pulsar as there is in our Sun, but the material tightly squeezed together. Pulsars give off energy as ordinary stars do, but they do not give it in a steady stream. They give off even bursts of energy, like a beating heart.

Quasars

Quasars appear as huge, dim stars, far out in space. They are not really dim. They are the Drightest things in space. They give off as much light as millions and millions of stars all rolled into one. Perhaps they seem dim because they are so far away.

Black holes 

Astronomers think that a black hole could be an enormous star that has shrunk until it is squeezed together so tightly that nothing is left of it but gravity. The pull of gravity would be so strong that nothing could get away from it, not even light. That is why they are called black holes.

Life of a star

Great clouds of gas and dust called nebulae, are found throughout the universe. Stars may form in nebulae. The process begins when gravity pulls the gas and dust particles together. As the mass of particles becomes tightly packed, or compressed, it heats up. In time, the temperature inside rises to over one million degrees Celsius. At such high temperatures, atoms of hydrogen gas begin to fuse together to form helium gas. As they do so, they release enormous amounts of energy, in the form of heat and light. The mass of gas and dust begins to shine as a star.

Red giant stars and white dwarf stars are stars that have grown old. When a yellow star, such as our Sun, gets old and ready to die, it swells up and becomes a red giant star. Then it shrinks and becomes a white dwarf. A white dwarf is a very heavy star. It swells into a super giant. It uses up the last of its energy and blasts itself apart in a supernova explosion. After a supernova, a tiny neutron star (smaller than our planet) may be left.

Heavenly bodies that emit and reflect light

Stars are the only heavenly bodies that emit light. They use nuclear fusion which produces enormous amounts of energy in the form of heat and light.

The Sun is the only object in the Solar System that generates and emits visible light.

Moons, planets, comets, and asteroids do not emit light. They reflect light.

Black holes absorb everything, including light.

The telescope

The simplest form of telescope has two lenses mounted in a long tube. The first lens, called the objective is a convex lens. This brings light from the distant object into focus. A small, real image is formed. The second lens, called the eyepiece is also convex, but it is much more powerful than the objective.

The eyepiece can be moved, so that the small image formed by the objective is at, or just inside, its focal length. It then acts as a magnifying glass and so, a much larger image is seen. In this astronomical telescope the image is upside down. This doesn't matter much when you are looking at stars!

Safety precautions to be taken when viewing the Sun

. Never view the Sun directly with the naked eye or with unfiltered devices such as,

. binoculars or a telescope.

. Project an image of the Sun through a telescope or binoculars onto a white screen.

. using binoculars, keep the cover on one of the tubes.

. Use pinhole projectors or certain type of solar filters.

. Use sunglasses made with special filters expressly designed for viewing the Sun.