Expert: James Gort - 1/18/2009

Question
QUESTION: Hi I was wondering if you can answer this question. why do all stars seem like there the same distance from earth. And does this have anything to do with the oblers paradox?

ANSWER: Hi Mike,

All the stars seem like they're at the same distance from earth because they're all so far away.  Although it takes about 8 minutes for light to travel to earth from the sun (93 million miles away), light takes over 4 years to travel to even the nearest star.  For most stars that we see, light has been travelling for hundreds or even thousands of years.  When things are all so very far away, we can't easily tell they're all at different distances from us.  To determine distances, there are a lot of "tricks" astronomers use - but that's another whole question!

The star's distances have little to do with Olber's paradox.  That paradox states that if the universe were infinite and filled with stars, in no matter which direction we'd look (even if the stars were very far away), we'd see a star, and the night sky would be very bright.  In reality, the universe is not infinite in size or age (current estimates put it at 13.7 billion years old), it is expanding, and stars don't live forever (they die and are slowly replaced with new stars).  These things combine to make the night sky dark, instead of completely filled with stars.

Hope that helps.

Prof. James Gort

---------- FOLLOW-UP ----------

QUESTION: Professor,
 Thank you for you quick and very informative response. If I read some other tings that don't quite make a lot of sense, Ill be sure to ask you! Thanks again,Mike

Answer
Hi Mike,

No problem.  I'll always try the best I can to make sense of it.  But believe me, there are some areas where no one has the answers or can make sense of it - although some try!  But I'll always let you know what's fairly well known; if not known - what's the best explanation; and if there is disagreement among the experts (and there's plenty of that!), I'll try and explain the difficulties.

Cheers,

Prof. James Gort