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Earth & Space - The Earth in space - Space & the Solar System - G18
This is the Teacher's Guide for this targetThis is the Teacher's Guide for this targetTeacher's Guide


The Milky Way

The Milky Way was the name given to the broad band of faint light which can be seen in the night sky when it is very dark. What you are actually looking at is the centre of our own galaxy. A galaxy is a collection of millions of stars which make and enormous spinning formation in the sky.

Our Solar System is about two thirds of the way out from the centre on one of the spiral arms, the Orion Arm.

Because we are in the galaxy, we do not get a clear picture of it. At the centre are older red and yellow stars whereas out on the arms are mainly hot, young blue stars.

The galaxy is vast - about 100,000 light years across (the Solar System is about 12 light hours across). The entire galaxy is spinning and it takes our Sun 220 million years to compete one lap!

(1 light year is about 9,460 billion Km.)                                 (background image)

Black Holes

Stars undergo a distinct cycle of being born from a nebula (a cloud of gases and other materials), building to become a star like our Sun. As the star ages it grows to become a Red Giant. Eventually this explodes, then collapses rapidly and the whole thing becomes very much smaller - a fraction of its original size. Because there is still the same amount of matter in the collapsed star, it is very, very dense with incredibly strong gravity- a teaspoon would weigh about a billion tons ! If the star was large to start with, this stage is called a black hole because gravity is so strong even light cannot escape. Black holes pull everything towards them and gradually suck things in and they disappear from the visible universe.


A galaxy is a huge mass of stars, nebulae ( a cloud of dust and gas) and interstellar material. The smallest contain about 100,000 stars whilst the largest contain up to 3 billion stars.

There are three main types, classified according to their shape: elliptical (oval shaped), spiral (have arms spiralling out from a central bulge) and irregular (no obvious shape).

Many of the ‘stars’ we see with the naked eye, can be seen with a powerful telescope, to be galaxies. The stars are grouped together in this way with nothing in between. Any individual stars we see are in our own galaxy.

(background image)

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