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Q: astronomy ( Answered,   2 Comments )
Question  
Subject: astronomy
Category: Science > Astronomy
Asked by: dylanbrady-ga
List Price: $10.00
Posted: 09 Aug 2006 04:30 PDT
Expires: 08 Sep 2006 04:30 PDT
Question ID: 754180
i have a question that my dad asked me. 
if you consider that the earth rotates about the sun, and that 'night
time' is always on the face of the earth that points away from the
sun, why is it that the field of stars we see doesnt change from
winter to summer, as the earth moves around the sun?
Answer  
Subject: Re: astronomy
Answered By: gregaw-ga on 09 Aug 2006 11:28 PDT
 
qed100 has it right.  The stars do change with the seasons, there are
just some that we can always see.

This page has a very good explanation of this.
http://www.nrc-cnrc.gc.ca/education/skies/cs-motions_e.html
"The Earth's annual orbit around the Sun, one Earth year or 365 
days, results in dramatic changes in the stars visible from any one
point on the planet. As the position of the Earth changes with the
seasons, different constellations come into view. For example, Orion
is not visible from May through July, but the circumpolar Big Dipper
is visible year round although its position changes in the sky."

Also check out the link on the page to the Planisphere:
http://www.nrc-cnrc.gc.ca/education/skies/cs-planisphere_e.html
With it you can determine what stars you can see at a given time of
the year and night.

Here is a downloadable, pc based Planisphere.
http://nio.astronomy.cz/om/


If you require any additional information please let me know by
posting a request for clarification.

Thanks and have fun enjoying the stars!
Comments  
Subject: Re: astronomy
From: jack_of_few_trades-ga on 09 Aug 2006 05:52 PDT
 
I could be way off here, so anyone please feel free to tell me I'm a moron...

We're always in the northern hemisphere no matter which side of the
sun we're on.  There is some change in the stars throughout the year,
but for the most part we are looking up at the same part of the sky
all year.
Subject: Re: astronomy
From: qed100-ga on 09 Aug 2006 10:40 PDT
 
The stars do change. 

   Go out in your yard (assuming you have a yard) at some time in the
evening when the stars are visible, shall we say for example 11:00 pm.
Look straight up and you'll see some portion of the sky, a
neighborhood of constellations. Then wait a few weeks. A month. Go
back to the same place in your yard, at the same time of day, and look
straight up. You'll see a different part of the starry sky, a
different neighborhood of constellations. The region you saw the month
before will be off to the west a ways. If you keep doing this each
month, you'll see yet another portion of the sky directly overhead
each time, with the portions seen the previous month offset to the
west. After one full year, you'll find yourself looking at the
original system of stars once again, and it'll all start over again.

   Earth orbits about the Earth/Sun barycenter once per year. Each day
it progresses about 1/365th of the way around, and so the sky visible
directly overhead at a given time of day also changes by about 1/365th
of one revolution per day. For any two consecutive days this
difference is small and may not be obvious, and so if one isn't in the
habit of noting the change over periods of weeks or months, it could
be mistaken for no change at all. But a thorough body of experience
over time reveals the changes in the sky, and the constellations
directly overhead in the middle of winter will be on the opposite side
of the sky from those of summer.

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