A Sense of Scale Page 6

The Milky Way, 100,000 light years

This map shows the full extent of the Milky Way galaxy - a spiral galaxy with at least two hundred billion stars. Our Sun is buried deep within the Orion Arm about 26,000 light years from the centre.

In our scale model the centre of the Milky Way lies at 236,000 km, which is about two-thirds on the way towards the Moon. The diameter of our galaxy is about 100,000 light years, corresponding in our scale model with a circle of 947,000 km, which is about 1.5 times the orbit of the Moon. See image below.


Image: Atlas of the Universe







The image to the right shows our scale model. The circle is the orbit of the Moon. The scale model of the Milky Way galaxy extends far beyond the Moon's orbit.



So with stars at about the size of 1 mm, a scale model of the Milky Way galaxy would be 1.5 times the size of the orbit of the Moon!










Pictures like the ones on this page and the previous page are deceptive because it looks like the stars are densely packed in the galaxy. But note that in our scale model the stars still have the size of a grain of sand and are at a distance of about 50 km to their nearest neighbour.

These images and also photographs from galaxies (as above) do not have enough spatial (angular) resolution to show individual stars. We only see a blurred image in which one pixel of the image contains millions of stars.