Re: True Time is Equinoctial *LINK*
Posted By: karibkween In Response To: True Time is Equinoctial *LINK* (karibkween)
Date: Friday, 25 March 2011, at 11:08 p.m.
In Response To: True Time is Equinoctial *LINK* (karibkween)
"Some of the statements above can be made clearer when picturing the day arc (i.e. the path the Sun tracks along the celestial dome in its diurnal movement). The pictures show this for every hour on equinox day. In addition, some 'ghost' suns are also indicated below the horizon, up to 18° down. The Sun in this area still causes twilight. The pictures can be used for both Northern and Southern hemispheres. The observer is supposed to sit near the tree on the island in the middle of the ocean; the green arrows give cardinal directions.
On the northern hemisphere, north is to the left, the Sun rises in the east (far arrow), culminates in the south (right arrow) while moving to the right and setting in the west (near arrow).
On the southern hemisphere, south is to the left, the Sun rises in the east (near arrow), culminates in the north (right arrow) while moving to the left and setting in the west (far arrow).
The following special cases are depicted:
The day arc on the Equator, passing through the zenith, has almost no shadows at high noon.
The day arc on 20° latitude: the Sun culminates at 70° altitude and also its daily path at sunrise and sunset occurs at a steep 70° angle to the horizon. Twilight is still about one hour.
The day arc on 50° latitude: twilight is almost two hours now.
The day arc on 70° latitude: the Sun culminates at no more than 20° altitude and its daily path at sunrise and sunset is at a shallow 20° angle to the horizon. Twilight is more than four hours; in fact, there is barely any night.
The day arc at the Pole: if it were not for atmospheric refraction, the Sun would be on the horizon all the time." Wikipedia
See Link for pictures
Day arcs of the Sun
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