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Earth’s Gravity and Orbit

What keeps the Moon going round the Earth? Why doesn’t it just carry on in a straight line? What keeps any smaller object in orbit around a much larger...

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What are Fraunhofer lines?

The Fraunhofer lines are any of the dark absorption lines in the spectrum of stars (like the Sun), which is caused by selective absorption of a star’s...

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How to get into Outer Space

Sending man-made objects into space is a very technically demanding and expensive process. To get into a close orbit around the Earth, an object must be...

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What is O B A F G K M?

When we look at the stars in the sky, a few have distinctive colours to the naked eye, like Rigel and Betelgeuse in Orion, but most of them appear just white...

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What are Circumpolar Stars?

A circumpolar star does not set, i.e. it is above the horizon all the time. What stars are circumpolar for a particular observer will depend on their latitude...

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What are Cepheid Variables?

We have seen how we can use parallax to find out how far away nearby stars are. What about stars further away from where the parallax angle is too small to be...

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