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winter solstice sunrise



 
 
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  #1  
Old December 1st 05, 09:22 AM posted to sci.astro.amateur
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Default winter solstice sunrise

Could anyone tell me how to calculate the position of the sunrise at
the winter sostice for a particular latitude. Thanks

  #2  
Old December 1st 05, 12:41 PM posted to sci.astro.amateur
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Default winter solstice sunrise

Teilo wrote:
Could anyone tell me how to calculate the position of the sunrise at
the winter sostice for a particular latitude. Thanks


Just use one of the popular planetarium programs readily available. If
you need further help, let me know your latitude and I will get you the
information from Chris Marriott's SkyMap Pro (an excellent program!).

Anthony.
  #3  
Old December 1st 05, 12:57 PM posted to sci.astro.amateur
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Default winter solstice sunrise

Thanks Anthony

My latitude is 52 degrees

Regards

Teilo

  #4  
Old December 1st 05, 04:01 PM posted to sci.astro.amateur
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Default winter solstice sunrise

Could anyone tell me how to calculate the position of the sunrise at
the winter sostice for a particular latitude. Thanks



Teilo, this page will calculate it for you...

http://aa.usno.navy.mil/data/docs/AltAz.html


-Florian


  #5  
Old December 1st 05, 07:41 PM posted to sci.astro.amateur
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Default winter solstice sunrise

Teilo wrote:
Could anyone tell me how to calculate the position of the sunrise at
the winter sostice for a particular latitude. Thanks


Assuming this isn't homework, use this formula:

azimuth = 90° +/- arcsin(sin(23.4°)/cos(latitude))

where +/- 23.4 degrees is the declination of the Sun at the solstices.
(It isn't that, exactly, but close enough for our purposes.) I use the
north = 0, east = 90 convention.

Thus, for instance, for your latitude of 52 degrees (north, I assume),
the formula yields

azimuth = 90° +/- arcsin(0.397/0.616)
= 90° +/- arcsin(0.645)
= 90° +/- 40°

If you're in the northern hemisphere, azimuth of the sunrise is thus 50
degrees at the summer solstice and 130 degrees at the winter solstice;
if you're in the southern hemisphere, it's vice versa. Note that at
latitudes above 66.6 degrees in either hemisphere (in the Arctic and
Antarctic circles, in other words), the argument of the arcsin function
is above 1, and the formula correctly indicates that the Sun does not
rise at all at the winter solstice.

Some calculators/computers use radians instead of degrees; if so, be
sure to take care with your units. Pi radians equal 180 degrees; or to
put it another way, one radian equals about 57.3 degrees.

This formula neglects two effects of some importance: refraction, and
the fact that in many places, sunrise is defined as the moment at which
the Sun's disc first peeks over the ideal horizon, not when its center
does. At temperate latitudes, the combined impact is to decrease the
azimuth of sunrise by a bit less than a degree in the northern
hemisphere, and to increase it by the same amount in the southern
hemisphere.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
  #6  
Old December 1st 05, 08:16 PM posted to sci.astro.amateur
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Default winter solstice sunrise

To Brian

The real astronomical relevence of the solstices is in the
asymmetrical relationship between the length of a day equidistant to
the Equinoxes.

The length of a day on Dec 21st in both hemispheres is asymmetrical
from the length of a day on June 21st,unfortunately you insist on
referencing the Sun's position off the Earth's Equator/axis allied to
the calendar system and dispense with the asymmetry provided by
variations in orbital motion.

Hemispherical or quasi-geocentric astronomy is great if you wish to
turn the great celestial motions into a personal sideshow but oh,what
an undignified thing to do.

There is an astronomical language waiting for genuine people who accept
that the great motions cannot be bottled into a convenient
calendar/celestial sphere bottle.There is also exciting avenues open
for those who detest insincerity, pretensiousness and laziness for none
of these things can have a part in astronomy and its noble
tradition,regardless of the many imposters who deign otherwise.

  #7  
Old December 1st 05, 10:25 PM posted to sci.astro.amateur
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Default winter solstice sunrise

Thanks all for your help.

John

 




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