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 is a planet?

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That’s a dangerous question!  Last time somebody asked it seriously, they demoted Pluto!  A planet is any object orbiting the Sun which is heavy enough to both squeeze itself into a spherical shape and clear the space around its own orbit (in other words, its gravity must be powerful enough that anything nearby gets drawn in and either smashes into the planet or gets catapulted away into space).  By this definition, we have eight planets in our Solar System.  It’s … Continue reading →

Why is Pluto not a planet?

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In 1930, Clyde W Tombaugh completed the search for Planet X, the outermost planet at the far reaches of the solar system.  This object was named Pluto.  Then, on 24 August 2006, the IAU (International Astronomy Union) formally voted on a new definition of the word ‘Planet’, which excluded Pluto.  For seventy-six years, our solar system had been understood to have nine planets, then suddenly it went back to eight.  The response was furious. Both the astronomical community and the … Continue reading →

What is the smallest planet?

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Mercury is the smallest planet known, with a diameter of just under 4900km.  Until it was disqualified as a planet in 2006, though, Pluto held the title at somewhere over 2300km – less than half the size!  Thanks to the formal definition of a planet, Mercury is not likely to lose its place at the bottom of the size ranks for a while: we can see quite clearly that there is nothing smaller in our Solar System which meets all … Continue reading →

What are shooting stars?

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“Shooting star” is the common name for a meteor, because it looks just like a regular star shooting across the sky.  The Solar System is full of dust and debris left over from when it first formed, and thousands of tonnes of this stuff falls on Earth every year.  When larger particles (about the size of a grain of sand) hit the atmosphere, they’re coming in at speeds up to 70 kilometers per second, and have a tremendous amount of kinetic … Continue reading →

What is the best way to observe a meteor shower?

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Meteor showers are one of the most accessible astronomical shows around.  They usually last several days, they can be seen by anybody with functional night vision, and they don’t need dark skies to be enjoyed.  Simply lie back and watch the shooting stars!  Best of all, there are many meteor showers which appear throughout the year. But if you simply head outside and look upwards on the right date, you might find the experience a little frustrating – time will pass, … Continue reading →