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Ask an Alien! Ask an Alien about Stars and Galaxies
Here are questions that visitors to this website have asked about Stars and Galaxies. If you want to ask a question, email it to Bob the Alien using this form.

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Question Answer
Chris (10) from South Africa asked:
I need to know an explain to the following questions:

Why do stars appear to move across the sky in the evening? Is this because the earth is rotating?

The other question was If you look at the sky between 7pm and 8pm and then again at 9pm, what will you see happening to the stars? Is the answer that they are moving across the sky ?
Hi Chris,

You are right about the reason the stars appear to move across the sky. It is because the Earth is rotating and not because the stars are moving - the stars stay where they are but because the Earth has span around a bit, they look like they have moved. It is difficult to notice the stars moving if you look constantly at the sky because they appear to move so slowly, but if you looked at the sky every few minutes, or, as in your example, once between 7pm and 8pm and again at 9pm, you will notice that they have all moved slightly. The Sun is actually a star and that moves across the sky in exactly the same way as the other stars simply because the Earth is rotating. If you see an object that looks like a star in the night sky, but doesn't appear to have moved with the other stars, you are actually looking at a planet!
Steven Powell asked:
How many stars are there in the solar system?
There is only one star in the Solar System - the Sun. It takes one full calendar year (365 and a quarter days) for Earth to spin around the Sun.
Do galaxies have planets in them or are they just stars? Galaxies are full of both stars and planets. It is believed that most stars have planets orbiting them. You actually live in a galaxy called the Milky Way, and the Sun is just one of billions of stars in your galaxy. Like the Sun, a lot (if not all) of the other stars in the Milky Way also have planets spinning around them.

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