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Name: Niall C McCann
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Question:
Someone told me that if you see an object in the sky which does not twinkle, it is probably a planet. If this is the case, why do stars twinkle? I have always noticed this star near the horizon in the winter in Ireland, and it shifts slowly through the visible spectrum. Is this due to the Earth's atmosphere/electromagnetic fields, or by gaseous clouds between Earth and the star?



Replies:
I suspect that bright, color-changing star is Sirius, the dog star. It is the brightest star visible from the Northern Hemisphere and is famous for appearing as different colors. I believe the color changes are due to the Earth's atmosphere (refraction effect).

It is the Earth's atmosphere that makes stars twinkle because they are so distant that they appear as point sources of light that are displaced by variations in our atmosphere. Planets do not twinkle being much closer, they are not point sources.

Hawley


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