NavList:

   

Reply

On 5/6/2013 12:27 PM, Frank Reed wrote:
> The (presumably) nearest to correct rule would be dip + 34'(for mean
> refraction) - 16'(for SD) or in other words dip + 18' (and to be yet
> more accurate, +/- a few minutes of arc for non-standard temperature and
> pressure).

It is not my wish to become the next "Noonan sunset" B.S. guy, but for
the life of me I cannot fathom the above, other than dip and
non-standard temperature and pressure corrections.

Which tables or refraction formulas (or derivations thereof) did you use
to determine a point observed at 34' would have an Hc of 0?

Whatever the observed stating point, 34' (or 28!65), is it cricket to
subtract 16'--an unrefracted semi-diamter from a  observed (squished by
refraction) sun? As you pointed out more than 90 moons ago, sun squish
near the horizon is not symmetrical, with the lower limb being raised by
refraction to a greater extent than the center point or upper limb. The
vertically refracted diameter near sunset should be approximately 27',
with the majority of the lift occurring between the 6'o'clock point and
a horizontal line between the 3 o'clock and 9 o'clock points. Refracted
lower vertical SD would be closer to 13' than 16'.

I can only surmise you worked refraction backwards, from Hc to Ho using
an Ho to Hc table or formula. As discussed in star-to-star measurements,
this may come very close for higher altitudes, but IMHO does not pass
the "...seat of the pants practical and mathematically elegant" test for
a sun near the horizon.

Given your education and expertise a betting man (myself included) would
give at least 1000 to 1 odds that I'm out in left field catching pop
flies, but it strikes me that Prof. Saemundsson's Hc to Ho refraction
formula would more appropriate than working backwards from the NA,
Bennett et al tables or formulas.

Bill B

   

Reply