5 Galaxies are groups of millions of stars, planets, gas clouds and rock fragments. Galaxies have different shapes: elliptical, spiral or irregular. The Solar System is located in one of the arms of a spiral galaxy called the Milky Way. Stars are enormous spheres of gas. They produce a great deal of energy. This is emitted in the form of light and heat. Stars vary in colour, size and brightness. – The hottest stars are white or blue. The coldest ones are orange or red. – In terms of size, they can be dwarf stars, giants or supergiants. – Brightness depends on their luminosity, which is the amount of light a star emits, and on their distance from Earth. The closest stars look brighter. 3 ●●○ Compare a star, a constellation and a galaxy. 4 ●●● DISCUSS with your partner. Why do we call our galaxy the Milky Way? B e a Sc i e nt i s t ! oBSERVE the night sky. Draw the celestial bodies that you can see in the sky with the naked eye. Which ones are the brightest objects? Celestial bodies The Universe is made up of stars, galaxies and many other celestial bodies. The Sun is a yellow dwarf star. STARS GALAXIES TH I N K AB0UT IT ! Constellations are groups of stars that look like a particular shape in the sky. They are named after objects, animals and mythological characters. For example, the Plough is part of a larger constellation called Ursa Major. Are the stars that make up a constellation connected to each other? We call it the Milky Way because… word bank celestial body galaxy Milky Way star Universe e i g h t y - n i n e · 89
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