Asked by Carol Johnson
With debris, dark matter, dust and up to 400 billion stars, our galaxy has an estimated mass of 3 trillion times our Sun. The Milky Way is a barred spiral galaxy with a flat rotating disc consisting of gas, dust and stars which is estimated to be between 100,000-120,000 light years across. This disc is composed of the familiar spiral arms, one of which plays host to our planet. These spread out from a central bulge with an average thickness of around 2,000 light years, where Earth is located, yet this is nothing compared to the central bulge of our galaxy with a thickness of around 30,000 light years.
Answered by Sophie Allan from the National Space Centre