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On 9/27/2012 12:47 PM, Alan S wrote:
> I wonder is the above mentioned in just a peculiarity of late Sept. when
> Sun's declination is so small, in some instances, less than 1D South.
> Any ideas or light to be shed.

Alan

Keep in mind that what you see is not what you get.  We are told with 0d
declination the sun will rise and set due east and due west,and night
and day will be equal lengths. This is not true for three reasons.

1. If the declination was 0d at LAN in September, the declination would
be N at sunrise and S at sunset.

2.Even if declination was 0d at rise and set, that would be for the
center of the sun, not the upper limb which we use to define rise and set.

3. Due to refraction, we are seeing a limb that is not there in a
vacuum. The refraction correction would be -0d 33!8 for the center of
the sun or upper limb on the horizon. Therefore it is quite possible to
have an Hc north of 90d or 270d near the autumnal equinox.  If memory
serves there is about an 8 day lag past the equinox before light and
dark are equal.

To make matters more confusing, 0d declination does not exactly define
the equinox as I recall. Somewhere in my archives there is an
explanation and diagram posted by a list member perhaps 7 years ago.
I'll try to locate locate that.

In memory of George I'll mention that when I learned the above I was as
disillusioned as a kid finding out his "sea monkeys" were nothing but
brine shrimp. This caused George to rebuff me as he asserted younger and
foreign list members had no idea what I was talking about. To get those
not in the know up to speed:
http://en.wikipedia.org/wiki/Sea-Monkeys

Bill B

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