The official definition of the speed of light in a vacuum is c = 299 792 458 meters per second. To help you make sense of this, here are some other ways of describing this: Light travels at just over a billion kilometers (or 600 million miles) per hour. If you could make a beam of light curve, and sent it on a trip around the Earth, it would make the journey 7 times in under a second. It takes … Continue reading →
There are some things that everybody knows without thinking about. The sky is blue, apples are red, water is wet, the Earth is round. But it’s important to regularly question ourselves and check for errors. It doesn’t take much thought to realise that the sky is usually NOT blue – on overcast days it is grey, at night it’s black, at sunset it can be practically any colour you care to name. Apples come in green varieties. When water freezes into ice, or … Continue reading →
Dear Urban Astronomer, Is it true that space junk is constantly falling down to earth? Should I be worried that I’ll get hit? Regards Cathrine Dear Cathrine Your letter included a link to this Washington Post article, which talks about UARS (Upper Atmosphere Research Satellite) which will be making an uncontrolled re-entry. At the time I write this, NASA’s best estimate is that it will re-enter the Earth’s atmosphere “Sometime in the afternoon” on Friday 23 September, New … Continue reading →
Comets have always been special. In ancient times, the sky was a stately ordered place, with the Sun, Moon, Stars and Planets all moving in their stately and predictable paths. But every now and then, something strange and new would appear. It would start as a fuzzy star with a misty trail behind it, growing from week to week until it formed a spectacular arc across the sky before fading away and vanishing. This was not a part of the … Continue reading →
As one of the classical planets, Venus has been a familiar sight to humanity ever since we first started looking at the stars. Like Mercury, Venus’s movements are bound to the Sun but the similarities end there. Venus moves more slowly, and wanders further. It also shines extremely brightly – only the Sun and the Moon are brighter than Venus. Venus is easily identified as the Evening or Morning star and often passes near to the Moon, putting on a … Continue reading →
