Dark matter is the name used for the material out in the universe which we cannot see, but can detect through it’s gravitational influence. When we look at galaxies, we can see a lot of matter in the form of stars, gas and dust. We can also see how the stars within those galaxies are moving in their orbits around the galactic core. The laws of physics tell us that these orbits should be at certain speeds, depending on … Continue reading →
Our galaxy contains over 200 billion stars, most of which are arranged in a disc containing a core and spiral arms. This disc is about 100 thousand light years across, but is only about 1000 light years thick. A small percentage of the stars are distributed around the Halo, which is a spherical cloud marking the boundaries of the galaxy. The halo completely envelops the disc, and is also home to many globular clusters. Comments? Questions? Why not mail … Continue reading →
As it stands, there is no formal definition for what makes a galaxy because, up till recently, astronomers have simply known them when they see them. This will probably be changing soon, as some astronomers have proposed a formal definition which will then be voted upon at a congress of the International Astronomical Union. Until then, we’ll stick with the traditional “Island Universe” definition: A galaxy is a vast structure composed of hundreds of billions of stars and enormous clouds … Continue reading →
The Cosmic Microwave Background (CMB) is a steady low-level microwave radiation that glows throughout the entire universe. It is the last echo of the heat of creation. For the first few hundred thousand years or so after the Big Bang, space was crammed full of a plasma of subatomic particles, so hot that they could not combine into atoms. But as it all expanded, the temperature dropped until suddenly it was cool enough that electrons could pair up with protons … Continue reading →
13.82 billion years old. This precise figure is thanks to the data collected by the Planck spacecraft, which was announced in March 2013. The previous best estimate was 13.73 billion years (give or take less than 1%), which came from the WMAP satellite. Both missions mapped out the Cosmic Microwave Background in unprecedented detail, allowing scientists to calculate the Hubble Constant. The Hubble Constant is the key value in the formula to calculate the age of the universe, which … Continue reading →
