Don’t you know you’re never supposed to ask a lady her weight? I can probably get away with telling her mass, though, which is about 4.87×1024 kilograms (Or to write it in tonnes: 4870 million million million tonnes). That means that Venus has about 82% of the Earth’s mass. Of course, mass and weight are two totally different things (even though the units we normally use for them happen to match up on the surface of the Earth). Like all … Continue reading →
Mercury doesn’t weigh anything at all – it’s in a state of freefall around the Sun (which we more commonly call ‘Orbiting’), so that it’s as weightless as an astronaut orbiting the Earth. It’s mass, however is 3.3 x 1023 kg (or three hundred and thirty million trillion tonnes!) – that’s a number so big that even economists can’t understand it, and yet it’s still the smallest planet in the Solar System by a long way. Written by Allen Versfeld Comments? … Continue reading →
Dear Urban Astronomer I’d like to know the deviation from true north of my compass, here in Johannesburg. I believe that true north is several hundred kilometres from magnetic north. How many degrees is that equivalent to? Sincerely, Yoram Bogacz Highlands North, Johannesburg Dear Yoram The magnetic north pole is actually about 1200km from True North, but the exact location of magnetic north varies from year to year (It is currently somewhere North of Canada, and is drifting East … Continue reading →
Update 5 June 2010: In less than a year, this article is already out of date. First, NASA’s STEREO satellites have been supplanted by SDO as the ultimate solar observatory, and it’s gorgeous high resolution images of the Sun currently dominate astronomy image galleries. Second, the Sun’s unusually long dormant period finally ended – there is now usually plenty for solar observers to see. And finally, I am no longer observing for ASSA‘s solar section – personal commitments have not … Continue reading →
A TLP (Transient Lunar Phenomenon) is an unpredictable, rare, mysterious glowing light on the Moon. The ‘Transient’ part of their name means that they’re very rare, and only show up for a very short time. They’ve been seen since astronomers first pointed their telescopes at the Moon, but are so elusive that in hundreds of years they’ve only been photographed a handful of times. They are a bit of a mystery, but one leading theory suggests that they are the … Continue reading →
