Expert: Steven LJ Russo - 9/26/2005

Question
-------------------------
Followup To
Question -
I sure hope you're able to answer this because I've had no success on another scientific question and answer site.

As the Earth travels around the Sun, why don't we see an ever changing panorama of stars in the night sky throughout the year?  If you take a tennis ball representing the Earth and move it around a baseball that represents the Sun, you can see that we should see totally different views of the universe at alternate seasons of the year; however, we don't.  There's only a slight shift in our view of the night sky from season to season which can be accounted for by the Earth's shift on its axis.

The only answer I can see is that the Earth must remain stationary in relation to the part of the universe we can see at night.  And this simply doesn't jive with the assumption that the Earth revolves around the sun.

Can you offer an explanation?

Many thanks in advance!
Answer -
Rich:

But we DO see different constellations throughout the year.  Although it really depends on Your Latitude.  Here in MY area (Albany NY), the only constellations that are visible all year are Big Dipper, Little Dipper, Cassiopeia, Cepheus, and Draco.  But all of the others change with the Seasons.

So as the Earth revolves around the Sun, we look into different parts of the Milky Way Galaxy.  So for example, we see Orion in the Winter, the Summer Triangle in the Summer, Leo in the Spring, etc.

Steve

Hi, Steve,

Thanks very much for your reply.  However, I have a follow-up question.  Why do we still see the constellations you mention all year long?  If you experiment with something to represent the Earth going around the Sun as in my first question, it appears that in winter the Sun should be right in between us and the entire segment of the universe that we see on summer nights.  In fact, during winter we only face that part of the universe during daylight hours.  And, likewise, on a winter's night, we should be facing the segment of the universe that would logically be on the opposite side of the Sun in summer, which we're facing only during our summer daylight hours.

In other words, how can we see ANY of the same constellations when they should be on the opposite side of the Sun in alternate seasons?  It's a little like when you're driving in your car; you can't see the same view through the windshield as from the rear view window at the same time (discounting mirrors).  If you sit in your car and look out of the side windows, you see the side view and only see a little of what's either in front or back of you by turning your head, similar to the Earth's shift on its axis during the change in seasons.  When you turn your head either way, you can only see part of the side view out of the corner of your eye; liken that to seeing some of the same constellations we can still see all year long.  

However, you're still mostly stationary.  And so it seems the Earth must be to account for all of this (except for its shift on its axis).

I didn't come up with this question myself.  Someone called in to a radio talk show a few months back and asked it.  It really threw me for a loop.  After giving it some thought and experimenting, I realized he was right.  If I could draw you a diagram, I'd be able to explain this to you much better.  

I hope you can help explain this paradox to me, as it's really bothered me and challanges what I learned in school.  By the way, I have a Bachelor of Arts in History with a minor in Business, class of 1974.

Thanks for your help!

Richard  

Answer
Rich:
You are explaining yourself perfectly and I understand your question.  I have the hard part of explaining why some constellations can be seen all year.  These are called "circumpolar Stars".  Quite frankly, I am the one who needs to draw the diagram.  Or actually, here is the BEST solution.

You need to go to your local planetarium, and have someone explain it with the use of their "star machine". I do not know where you live, or I would reccommend the planetarium to you.

Steve