Small Scope Observing/Thoughts

Sketcher wrote in message . ..

On February 7, 1998 I observed the Crab Nebula when a gibbous (9 day
20hr 54min old) moon was 5 degrees 40 minutes distant from M1. The
Crab was visible with 20x80 binoculars as well as with a 25cm
Newtonian stopped down to a 4 inch aperture. This was from a rather
clean, rural Montana sky. Of course, a full moon is brighter than
even a gibbous moon . . .

Yes, a full Moon is at least 3X brighter than a 9-day gibbous Moon --
a huge difference! On the other hand, the sky 6 degrees away from the
Moon is many times brighter than the sky 90 degrees from the Moon.
Oh yes, and there's about a 30% difference between a perigee full
Moon and an apogee full Moon.

As a rule of thumb, figure that the zenith is about as bright in the
country at a full Moon as it normally is in a typical densely populated
suburb, or a sparsely populated city. (Almost all western cities count
as sparsely populated.) If you're right near a car dealer, a prison,
or a poorly lit shopping center, the sky may be much worse, regardless
of population density.

A typical dark suburb is about one magnitude darker than that. At
that level, a 50% illuminated Moon has only a very minor additional
effect on the sky brightness, unless your target is right near the
Moon.

I certainly can see M1 in my 70mm refractor from here in Cambridge,
Massachusetts, and to me it's not even all that hard, but I'm sure
it would stymie almost all beginners.

- Tony Flanders