The Milky Way

On a dark night with transparent skies, we can see a band of light across the sky that we call the Milky Way. (This comes from the Latin − Via Lactea.) The light comes from myriads of stars packed so closely together that our eyes fail to resolve them into individual points of light. This is our view of our own galaxy, called the Milky Way Galaxy or often ‘the Galaxy’ for short. It shows considerable structure due to obscuration by intervening dust clouds. The band of light is not uniform; the brightness and extent is greatest towards the constellation Sagittarius, suggesting that in that direction we are looking towards the Galactic Centre. However, due to the dust, we are only able to see about one-tenth of the way towards it. In the opposite direction in the sky the Milky Way is less apparent, implying that we live out towards one side of the Galaxy. Finally, the fact that we see a band of light tells us that the stars, gas and dust that make up the Galaxy are in the form of a flat disc (Figure 14.1).

A detailed image of the centre of the Galaxy in the constellations Sagittarius and Scorpius is shown in Figure 14.2.