“Nebula” is the Latin word for cloud.  It was originally used to describe anything in the night sky that had a cloudy or diffuse appearance, and that wasn’t a comet.  Early in the 20th Century, however, it was discovered that some of these nebulae were actually “island universes” (galaxies or globular clusters).  Since then, the word refers to specific types of objects: Planetary nebulae are usually spherical and are the expanding shells of material ejected from dying stars.  They get … Continue reading →

Gravity is the force that attracts objects with mass towards each other.  On Earth, it is what brings us back to the ground if we jump upwards.  In space, it is what makes the Moon orbit the Earth, what makes the Earth and other planets orbit the Sun, and what makes the Sun and stars orbit the centre of the galaxy.  According to physicists, there are only four forces in the universe, and gravity is the weakest by a ridiculously … Continue reading →

  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 →