Category Archives: Astronomy 101

One of my main goals is to try and share a bit of knowledge and understanding about the incredible universe. I have been steadily writing and posting various articles to explain and educate the masses (that’s you, dear reader!) a bit more about some of the science behind the hobby. An urban astronomer might never see most of the things we talk about here, but it’s still good to know about them.

What does Mercury weigh?

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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 →

How far does True North deviate from Magnetic North?

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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 →

How can I safely look at the Sun?

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 Update 5 June 2010: In less than a year, this article is already out of date.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 →

What are Transient Lunar Phenomena?

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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 →

Why does Earth not have rings?

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Dear Urban Astronomer After reading your article about the rings that they found around that exoplanet, I wondered why Earth does not have rings? You mentioned that a lot of the planets in our own solar system have them, so why not us? Thanks, Wantum Rings   Dear Wantum   The planets in our Solar System which have rings are Jupiter, Saturn, Uranus and Neptune.  These four planets have a few other things in common as well:  They all have lots of moons, … Continue reading →