As of 11 July 2012, we know of five moons around Pluto. The largest, Charon, was discovered in June 1978, and is closer to its parent in size than any other moon in the Solar System. In fact, when it was first discovered it was found that the combined mass of the two had thrown out all calculations of Pluto’s size. Up till then, Pluto was assumed to be much larger than we know it is today. The next two … Continue reading →
When a star runs out of fuel to burn, it’s outer layers get ejected into space and it’s core collapses under gravity into a white dwarf. If the star was really big, more than about 8 times the mass of our Sun, then it continues to collapse, becoming denser and denser until the very atoms themselves are crushed. The enormous gravitational pressure overcomes the Weak Nuclear Force, so that electrons fall out of their orbit and touch the protons … Continue reading →
Stars go through a number of changes as they pass through different life stages. If a star doesn’t have more mass than about eight times that of our own Sun, then it will end its life as a White Dwarf. White dwarfs are extremely small, hot and compact objects, composed of degenerate matter, and are all that remains after the original star runs out of fissionable fuel and ejects its outer layers into space. What remains is usually around … Continue reading →
Dear Urban Astronomer Talking about the thunder storm in Pretoria last night, a co-worker of mine mentioned that she covered all the mirrors in her house because they can “catch and reflect” lightning… She said that lightning can behave like light and be reflected. I argued that lightning is not light, but a raw, electrical charge… I have never heard of this practice, and although it sounds like superstition to me, I was wondering if there is any truth in … Continue reading →
“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 →
