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#1
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Stupid question perhaps...
I guess I am missing something obvious but I don't know what.
Lets say: S = Sun St = star E = Earth OK, in winter we have ______________________S______________E_________- _______________________St So the earth is on the "left" of the sun (I know there is no left or right in space but bear with me). During the night, the star can be seen because the dark side of the earth is facing that direction. Six months pass: _- __E_______________S_______________________________ ____________________St This time the dark side of the earth is facing the opposite direction (I know, no absolutes etc). So, surely there should be a massive change in the visible stars between seasons? But is there such a difference? I thought that most stars are visible all year round. That doesn't see to fit with that I have above. Can anyone explain it in simple terms? |
#2
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Stupid question perhaps...
On Jul 21, 1:30 am, cqmman wrote:
I guess I am missing something obvious but I don't know what. Lets say: S = Sun St = star E = Earth OK, in winter we have ______________________S______________E_________- _______________________St So the earth is on the "left" of the sun (I know there is no left or right in space but bear with me). During the night, the star can be seen because the dark side of the earth is facing that direction. Six months pass: _- __E_______________S_______________________________ ____________________St This time the dark side of the earth is facing the opposite direction (I know, no absolutes etc). So, surely there should be a massive change in the visible stars between seasons? But is there such a difference? I thought that most stars are visible all year round. That doesn't see to fit with that I have above. Can anyone explain it in simple terms? There is exactly that massive change. When you look at say Scorpius (to the South) in the summer at midnight, six months later at midnight you wont see Scorpius at all it will indeed be opposite the Sun, Instead you will see Orion. The thing is that during the course of a night you can see much more than half of the sky (unless you are located at one of the poles ;-)). Just after sunset looking straight up you are looking more or less at right angles to the line between the Sun and Earth. A few hours later at midnight, straight up is now opposite the Sun, a few hours later again just before dawn, straight up is again at right angles to the Earth - Sun line but in the opposite direction to what it was just after sunset. In the winter when the twilight is short you can of course see more than in the summer. You are also limited by you latitude. At the poles you can only ever see half the sky, whereas at the equator you can see nearly all of it in one night except that part of the sky close to the Sun. If you move south of the equator for example you can't see Polaris at any time of year or night. When you are looking at Polaris in the Northern hemisphere and the stars near it you will notice that during the course of a night these stars never set, they are said to be circumpolar. They are even always in the sky during the day. To explore the sky and what you will see from your location at various times of year, I recommend you download a planetarium program. You tell the program where you are located - they usually have lists of most cities in the world or you can enter your latitude and longitude. The program will then display the sky based on the clock on your computer but you can change that to set any time and date you like usually +/- a few thousand years from the present. Here is a very good freeware program called Skycharts - probably has a lot more features than you will ever need. Select the link that says 'Complete Package' (don't worry about all the optional star catalogues and stuff listed) http://www.stargazing.net/astropc/download.html |
#3
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Stupid question perhaps...
On 20 Jul, 15:44, wrote:
The thing is that during the course of a night you can see much more than half of the sky (unless you are located at one of the poles ;-)). Just after sunset looking straight up you are looking more or less at right angles to the line between the Sun and Earth. A few hours later at midnight, straight up is now opposite the Sun, a few hours later again just before dawn, straight up is again at right angles to the Earth - Sun line but in the opposite direction to what it was just after sunset. Cool. Thanks very much for explaining it all. |
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