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Name: niall c mccann
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1993 - 1999


Question:
This question has probably been asked before but, here goes: Someone told me that if you see an object in the sky which doesn't twinkle, it's 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? Someone please have a go at answering as this is bugging me. :-)


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).

And yes it's true that stars twinkle and planets dont. The reason is the immense distance of stars compared to planets: there's enough "stuff" (gas and dust) out there in interstellar space that causes the twinkle. OOPS! It's 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 don't twinkle being much closer, they are not point sources.

(Thanks to RC Winther for drawing this to my attention)

john



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