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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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  #11  
Old 02-04-2010
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Originally Posted by Boasun View Post
You wouldn't by chance be referring to the Diurnal circle...Which is the path of a celestial body during its daily apparent revolution around the earth.
The sun's diurnal circle would be a subset of this set of all possible points. What would you get if you took the globe and drew the diurnal circle for every day of the year? ... for every year, ever?
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The sun's diurnal circle would be a subset of this set of all possible points. What would you get if you took the globe and drew the diurnal circle for every day of the year? ... for every year, ever?
AdamLein, are you referring to the celestial sphere ?
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My turn ..

Without a sextant, what simple method can you use to find your latitude in the northern hemisphere ?
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Old 02-04-2010
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measure the angle of Polaris above the northern horizon?
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measure the angle of Polaris above the northern horizon?
Correct.
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Here is a two point question ...

If you draw a line through the center of the earth to the center of the Sun, when will someone in Boston be nearest to that line ?
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Last edited by wind_magic; 02-04-2010 at 05:21 PM. Reason: sp
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Old 02-04-2010
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This link was useful for the first 2 questions: Journey North: Mystery Class
When viewed from a North Pole orientation:
Earth orbits the sun in a CCW direction.
Earth also rotates or spins in a CCW direction so the sun appears to rotate the earth in a CW fashion since it is relatively standing still compared to the earths rotation on its axis.
The moon is a trickier beast and appears to rotate around the earth in a CW direction which is due entirely to the earths rotation again. The moon is actually orbiting the earth in a CCW direction.

The next question: "What would you get if you took the globe and drew the diurnal circle for every day of the year? ... for every year, ever?" smells like a trick question to me since it includes every year, ever.
If I were to assume the last 1000 or 10,000 years the suns path across the sky would form a doughnut or taurus shape. There is some conjecture that the earth took on its current axis and rotation from collisions with an asteroid in the not so measurable past.
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Here is a two point question ...

If you draw a line through the center of the earth to the center of the Sun, when will someone in Boston be nearest to that line ?
I'm thinking twice a year, at local area noon on the longest day in summer and around midnight on the shortest day of the year, but I'm shooting from the hip. (longest and shortest day for the northern hemisphere)
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I'm thinking twice a year, at local area noon on the longest day in summer and around midnight on the shortest day of the year, but I'm shooting from the hip. (longest and shortest day for the northern hemisphere)
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.
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Old 02-05-2010
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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 ?
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