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On Sep 29, 2004, at 10:57 PM, Alexandre Eremenko wrote:

> Fred,
> Finally I obtained a relally good measurement for
> Vega-Arcturus distance!
>
> Sept 29, GMT 0h5m:
> Arcturus-Vega, alt(Arctur)=30d, alt(Vega)=83.
> Galileo scope, 4x40:
> SEXT DIST           ERROR
> 59d06.5'            -0.6'
> 59d06               -0.1'
> 59d08.3'            -2.4'
> 59d06.6'            -0.7'
> 59d05.8             +0.1'
> 59d05.7             +0.2'
> Kepler (inverting) scope 7x30 with cross-hairs:
> SEXT DIST           ERROR
> 59d05.8'            +0.1'
> 59d06.0'            -0.1'
> 59d05.9'             0.0'
> 59d05.8'            +0.1
> 59d05.8             +0.1

> It is interesting: I am somewhat confused because the Russian manual
> calls the Galileo scope "the night scope" and the inverting one
> "the day scope". The manual says: "attach the inverting one for Sun
> observations and the Galileo for night observations.

Alexandre,

That is indeed a good result!  It looks like your sextant is both
accurate and precise at that angle, which one would expect in a new
instrument.

One quibble, the inverting scope probably is not 7x30.  The 7 refers to
the magnification, and the 30 to the diameter of the objective lens in
millimeters.  I expect your inverting scope probably has a diameter of
about 15 mm.

The reason the Galilean scope is preferred for star _altitudes_ is that
it probably has a much larger objective than the inverting scope.  Thus
it gathers more light, making it easier to see stars at dusk, when the
horizon is still visible.  For sun shots during the day, the greater
magnification of the inverting scope makes it more accurate; there's no
need to admit more light to make the sun visible.

According to Bowditch via Bruce Stark, the inverting scope is preferred
for lunars, and presumably would be preferred also for star-to-star
shots.

Hopefully, I will acquire a good 7x scope before long and be able to do
better with stars and lunars.

Fred

   

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