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 →

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 →

A dwarf planet a member of the Solar System that doesn’t quite meet the definition of a planet.  It is defined as an object that is in orbit around the Sun, that has enough mass for its self-gravity to squeeze it into a mostly spherical shape, that has not cleared the neighbourhood around its orbit, and that is not a satellite.  The most famous dwarf planet is Pluto, but others include Haumea, Makemake, Eris and Ceres (which is also the … Continue reading →