Category Archives: Questions and Answers

Most people have many questions about astronomy, and aren’t happy with the standard answers. Here are some articles trying to change this. If you have any questions you would like to see answered, ask me in an email to the address below, and I will answer your question in an article on this list

What is a galaxy?

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As it stands, there is no formal definition for what makes a galaxy because, up till recently, astronomers have simply known them when they see them.  This will probably be changing soon, as some astronomers have proposed a formal definition which will then be voted upon at a congress of the International Astronomical Union.  Until then, we’ll stick with the traditional “Island Universe” definition: A galaxy is a vast structure composed of hundreds of billions of stars and enormous clouds … Continue reading →

Which telescope?

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Newcomers to astronomy commonly ask, “What telescope should I buy?”.  First, the easy answer:  Buy a six inch newtonian reflector, with two or three eyepieces, and be sure to not buy it from any place that doesn’t specialize in telescopes (although you might be safe with a large photographic shop, if they have staff who have actually used telescopes to look at the stars).  The problem is that telescopes are currently available in a mind boggling range of prices, designs … Continue reading →

If a spaceship shoots its guns

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Dear Urban Astronomer I am busy designing a science fiction computer game and am trying to figure out the physics of combat.  If a spaceship is flying through space and shoots backwards, what exactly does the bullet do?   Regards KJM Confession to the reader:   Unlike all the other questions I answer in this section, this was not posed directly to me in an email.  Instead, I happened to catch a friend from Twitter posing the question to the … Continue reading →

What is the Cosmic Microwave Background?

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The Cosmic Microwave Background (CMB) is a steady low-level microwave radiation that glows throughout the entire universe.  It is the last echo of the heat of creation.  For the first few hundred thousand years or so after the Big Bang, space was crammed full of a plasma of subatomic particles, so hot that they could not combine into atoms.  But as it all expanded, the temperature dropped until suddenly it was cool enough that electrons could pair up with protons … Continue reading →

How old is the universe?

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13.82 billion years old.  This precise figure is thanks to the data collected by the Planck spacecraft, which was announced in March 2013.  The previous best estimate was 13.73 billion years (give or take less than 1%), which came from the  WMAP satellite.   Both missions mapped out the Cosmic Microwave Background in unprecedented detail, allowing scientists to calculate the Hubble Constant.  The Hubble Constant is the key value in the formula to calculate the age of the universe, which … Continue reading →