Category: Science > Astronomy
Asked by: dylanbrady-ga
List Price: $10.00
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?
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 ¼ 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!
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.
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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