[TenTec] Equinox Day

[Jim Reid]

Carl, N4PY,  wrote:


> The refraction of the Earth's atmosphere increases the 
> amount of daylight by about 2 minutes at sunset and about 
> 2 minutes at sunrise for latitudes below about 40 degrees.  
> Add to that another minute for the diameter of the sun on
> each end and you have a total of 6 minutes added to daylight. 

Do programs,  such as my GeoClock,  account for that refraction,
or do they just calculate based upon the geo center of the
Sun's actual disk,  or the "apparent" disk as caused by this
refraction?  I recall this came up once before,  when the
program reported, at equinox,  that the Sun's center would
be on the horizon at both the North and South poles.  Because
of refraction,  it was said then,  that the Sun would never be
seen simultaneously at both poles (nor any part of the Sun
simultaneously,  hi).
 
> But the true equinox is the same everywhere on the earth 
> and that occurs the instant the center of the sun passes 
> through the plane of the Earth's equator.  This is  0100 GMT 
> on March 21 this year.

I guess that is the true "definition" of equinox,  but we will not
have equal hours of sun up and sun down that day here.  I'll
have to remember to look to see what the sunrise and
sunset times are here on the 21st.

Something else to do until an Orion is shipped out here!

Do you suppose my GeoClock (V8.4) knows about the refraction?
That program is the source of my trivia info about this day,  hi.

73,  Jim  KH7M