Dear Urban Astronomer How exactly do satellites work? Who invented them, and how many are up there now? I heard somewhere that there must be millions! Is this true? Yours Curious Dear Curious All artificial satellites have one thing in common: they are in orbit around something (usually the Earth), and will in theory stay up there indefinitely all by themselves. If by “How do they work”, you meant “How do they stay up there”, then prepare for a … Continue reading →
When you have two bodies orbiting each other (For example, the Earth and the Moon), we call the smaller of the two the Satellite of the larger. Thus the planets are satellites of the Sun, the Moon is a satellite of Earth, and so on. But when most people talk about satellites, they are referring to artificial satellites. These are manufactured objects which have been launched into space and carefully maneuvered into orbit around something much more massive like a … Continue reading →
Current total: 95. I’ll keep updating this page as more get discovered. Details in the UPDATES section below As of 2 February 2012, we know of 67 moons around Jupiter. We will probably continue to find more and more, as we keep looking, since Jupiter is large enough that it constantly captures passing asteroids and comets, turning them into moons. The smallest ones are so hard to see, and have such big irregular orbits, that astronomers sometimes lose them, until … Continue reading →
Edit: This article was posted on 21 June, the very day that the email discusses. Obviously it would have been simpler to just say “Stick your head out the window. How many suns do you see? Any questions?”, but emails like this tend to get recycled. Some genius adjusts the date (that “Mars as big as the Moon” hoax has hit my inbox every august for years now) to move the supposed event back into the future, and the … Continue reading →
To understand degenerate matter, we’ve got to step back and look at regular normal matter first. If you’ve had even a rudimentary physics education (high-school level or higher), you’ll be aware of the gas laws. Pressure and volume are proportional to temperature, so that if you increase the temperature, the gas will try to expand (and if it is prevented by expanding by being sealed in a container, the pressure rises). These principles explain how a hot air balloon flies, … Continue reading →
