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Name: Kristina Matarazzo, Mary, and Burbank School
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Question:
Why do stars always stay in the same place. For example, I can always find the constellations. Why do not the stars change into other constellations?



Replies:
Stars seem to stay in the same place for a long time, long compared to our lifetime. This happens because of the large distance that separates us from the stars. We can observe only changes in the angular position of stars. An object at distance D will appear to move by one degree across the sky if it moves a distance D/60. For a star at a distance of few light years from us, this displacement is also of the order of a light year. Given the average velocity of stars, this distance will be covered in a few thousand years So these two reasons contribute, large distance to stars and small relative velocity of stars, in making stars appear stationary.

Jasjeet S Bagla


Constellations are human inventions. Usually the stars that make up a constellation have no relation to each other; they are generally not part of the same cluster (an exception is the Big Dipper; many of its stars actually do belong to a single open cluster.) A very bright star that is very far away may look similar to a dimmer star that is closer; and if we see two (or more) similar-looking stars in the same part of the sky, it is not unreason- able to associate them. It is believed that the constellations were originally invented thousands of years ago as an aid for learning the stars so that they could be used for navigation by sailors.

RC Winther


They form in the minds of people looking at the stars! Most of the stars in constellations are actually very far apart from one another. All we can tell is how bright the stars look from here and where they are in 2 dimen- sions - the angular position in the sky. We cannot tell right away how far they are, and that means that stars that may look like they are forming a group together are actually in totally different places. The constellations are a useful way of getting to know the night sky, however - they make the patterns of stars very recognizable, and if you go look at them once a week or so you will soon know them very well!

A Smith


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