NavList:

   

Reply

The value in the almanac for SD of the Moon
is not only rounded too much but it is also too small.
Apparently they compute it "as seen from the center
of Earth".
The real value depends on the Moon's altitude and it
is given by approximate formula

SD=0.27277HP(1+sin(HP)sin(ALT)),

where HP is the Moon Horizontal Equatorial Parallax
(rightmost column of the Moon section of the daily page)
and ALT is the Moon altitude.
The second term is non-negligible if we talk about 0.1'
precision!

Computation with this formula shows that all
my (and Frank's) recently mentioned measurements
of IC using Moon are acceptable, that is 4SD is
within 0.4 from the true value.

It remains to explain why star and Sun tests give
consistently
smaller IC than the Moon test (at least in my measurements).
It is interesting how various authors rate the
various tests
for IC in the order of decreasing precision.

Heath (of Hezzanith): Star, Horizon, Sun.
Russian manual: Sun and Star equally good, then Horizon.
(They quote the statistics that the typical
accuracy of the Sun/star test is 0.1 to 0.2, while
the Horizon gives only 0.5.

I've never seen the Moon mentioned for IC tests,
before Frank's messages.

Today I also tried wires. Computation shows that to achieve
0.1 accuracy of the test, the wires have to be at
least 1 nautical mile away. It is really hard to see
any wire
at this distance., even with a 7x telescope.
At least at my age:-(

Alex



--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply