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

Six Thousand Years, or 13.7 Billion?

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Every now and then, when people learn that the Urban Astronomer is a Christian, some wag asks “So why should we take you seriously if you believe that the universe is six thousand years old?”.  And I battle to answer, because where do you start with such a retarded question? See, the latest round of partisan thinking is “Almighty Skeptical Atheism” vs “Almighty Faith-based Literalist Christianity” (since, as the dominant religion in the West, Christianity is the obvious target for … Continue reading →

What is the Earth’s escape velocity?

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Escape velocity from the surface of the Earth is about 11.2 kilometers per second (or just over forty thousand km/h, or twenty five thousand mph), meaning that if you want an object to leave Earth and never fall back, you have to throw it at least that fast.  How does that work?  Well as you’ll remember from high school physics, Newton’s law of universal gravitation tells us that an object’s weight (The downward force applied by gravity) depends inversely on … Continue reading →

What is an equinox?

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An equinox is a point in the Earth’s orbit when day and night are both exactly the same length.  There are two equinoxes (or equinoctes if you want to be excessively correct) each year, but they also mark the change of the seasons between warm and cold.  The Earth’s axis is tilted, so that for half of each year, one hemisphere is tilted towards the Sun, so that it gets more heat and light from the Sun that the other. … Continue reading →

What does Jupiter weigh?

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Jupiter has a mass of about 1.9 x 1027kg – 1900 trillion Trillion kilogrammes.  That’s more than double all the other planets, asteroids, comets and dust of the entire Solar System put together.  Jupiter is BIG, yet still manages to not weigh anything at all.  How?  Because it is in orbit around the Sun, just like an astronaut orbits the Earth, and so experiences zero gravity.  That’s not to say there is no gravity around Jupiter – it has plenty gravity … Continue reading →

What does Mars weigh?

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Mars does not have a weight, but does have a mass of about 6.4 x 1023 kilograms, which is a little more than a tenth that of Earth.  When astronauts or spacecraft orbit the Earth, we describe them as being weightless, because they are in freefall.  They are not resisting gravity (the way your body does when you stand on the ground) so “Weight” becomes a totally meaningless concept when you’re in space.    Written by Allen Versfeld Comments?  Questions? … Continue reading →