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Go Back   SailNet Community > General Interest Forums > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #21  
Old 02-05-2010
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Quote:
Originally Posted by wind_magic View Post
AdamLein, are you referring to the celestial sphere ?
I haven't seen an answer to this one yet, so....

The sun's geographical position is the place on the Earth directly under the sun, so this is just the set of all possible places where the sun can ever be directly overhead. This is what the tropics are.
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  #22  
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Originally Posted by wind_magic View Post
That's correct, and it was a trick question because most people would just guess noon on Midsummer's day and would not think of midnight on Midwinter's night. Very good.

That's why you can see so many southern stars at Midwinter's.
This is assuming that the line extends in both directions from the center of the Earth

And I think the amount of the southern celestial sphere visible from a given north latitude is the same every night of the year... though the sun being closest to the local nadir would probably make the sky darker. Is this what you were getting at?
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  #23  
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Originally Posted by AdamLein View Post
I haven't seen an answer to this one yet, so....

The sun's geographical position is the place on the Earth directly under the sun, so this is just the set of all possible places where the sun can ever be directly overhead. This is what the tropics are.
Ahh, now that you say what the answer is it is obvious.
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Originally Posted by AdamLein View Post
This is assuming that the line extends in both directions from the center of the Earth
If you go back and look at my original question I said "through the earth", but that was only after I posted it and immediately edited it for the very reason you say, originally it said from the center of the earth to the center of the Sun, not through the center of the earth to the center of the Sun.

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And I think the amount of the southern celestial sphere visible from a given north latitude is the same every night of the year... though the sun being closest to the local nadir would probably make the sky darker. Is this what you were getting at?
No, I'm talking about stars below the celestial equator. During the summer the celestial equator is near the horizon at night, but during the winter the celestial equator is very high in the sky, and the stars to the south of the celestial equator are what I meant by "southern stars".
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Last edited by wind_magic; 02-05-2010 at 07:54 AM. Reason: Edit
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Old 02-07-2010
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During the winter in the northern hemisphere, what is the name of the small tight cluster of stars that moves along north and west of Orion ?
I believe you are referring to the Pleiades.
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What term refers to the amount of time since a celestial body has crossed the local meridian?
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I believe you are referring to the Pleiades.
That's right, or the "Seven Sisters". Very obvious cluster near Orion in the constellation Taurus, looks a lot like a small version of the little dipper to me, visible in winter (Edit - when it isn't obscured by trillions of snowflakes falling from the sky)
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Old 02-10-2010
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What term refers to the amount of time since a celestial body has crossed the local meridian?
Time's up: it's the local hour angle.

Next question: I observe a star near the horizon. All throughout the night it moves leftward along the horizon, without changing altitude. Where am I?
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Time's up: it's the local hour angle.

Next question: I observe a star near the horizon. All throughout the night it moves leftward along the horizon, without changing altitude. Where am I?
Antarctic circle ? Is there such a thing, or is it the arctic circle in the south ?

That's mostly a guess, by the way ...
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WM: you're close...
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