What is the Milky Way?
The Milky Way is a huge mass of gas and stars that can be clearly seen as a band of light across the night sky.
The Earth and everything else in the Solar System is part of the Milky Way. It is known as our Galaxy. It is so huge that light takes nearly 100,000 years to travel from one side to another. Where stars are packed close together the Milky Way is bright, but huge clouds of gas and dust block the light from the other parts of the Galaxy. These clouds prevent astronomers from observing the whole Milky Way.
The super supernova
Sometimes a star appears in the sky quite suddenly. This happens when there are pairs of stars rotating together. These are called binaries, and there is usually one large star called a red giant, orbiting with a smaller, hotter star. The nova takes place when gas is drawn from the red giant into the smaller star, where the heat causes a massive explosion and emits huge amounts of light. A supernova takes place when a star collapses as it begins to burn out, then suddenly explodes, producing a huge amount of light energy, and leaving behind a tiny core of neutrons, which is the heaviest substance in the Universe. A pinhead-sized mass of neutrons weighs many thousands of tonnes.
How does gravity work?
The force of gravity is the attraction between every piece of matter, even the smallest particles. The more matter there is in something, and the closer its particles are packed together, the stronger the attraction. Stars are large and very dense bodies, and so they have a strong field of gravity. It is our Sun’s force of gravity that holds the planets in their orbits. The Earth’s gravity keeps the Moon in its orbit. Small bodies such as the Moon have a very weak gravity. This explains why astronauts on the Moon’s surface were able to jump up high with very little effort.
Alien Life
No one has yet shown that life exists on other planets. However, as there are billions of stars, some with planets, it seems unlikely that Earth is the only place with the right conditions for life. Astronomers use radio telescopes to search for messages from other civilizations. In 1963 they thought they had found the first traces of intelligent extraterrestrial life when regular pulses of radio waves were detected. In fact they had found strange distant galaxies called quasars.