Limiting Magnitudes, Plans, etc.

Date: 15 February 2007 U.T.
Time: 3:00 - 3:40 U.T.
NELM: 6.6
Temperature: -9 F (-23 C)

During the lengthy cloudy spell I revised observing projects, etc. A (new) home-made, square, eyepiece field stop was fabricated that includes a means to more accurately determine angular size as a fraction of the field of view. Refinements were made on a deep-sky project geared toward an all-sky, telescopic survey. Rough plans were drawn up for systematically sketching (mapping) the entire visible portion of Earth's moon.

I'll be as surprised as anyone if I actually manage to succeed in seeing these plans through to their natural conclusions! I'm easily distracted by a bright comet, a well positioned planet, other projects, etc.

I dug up some 'new' limiting magnitude charts that should allow me to make nightly estimates on the limiting magnitudes of my binoculars. I wore red goggles inside a dimly illuminated room for half an hour or so to aid in dark adaptation prior to going outside.

Once outside I used my new charts to determine my Naked-Eye Limiting Magnitude (NELM). Next I repeated the procedure using 8x42 and 20x80 binoculars, both hand-held. I have little doubt that a solid tripod would increase the binocular limiting magnitude. Eventually I'll need to check that out . . .

The limiting magnitude of the 8x42 binoculars was about 10.0. That of the 20x80 binoculars was about 11.4. All values, including the NELM were adjusted for the zenith -- one tenth of a magnitude was added from what was seen in the 45 degree altitude star fields. With practice these values should become more reliable. I hope to eventually correlate the various measurements with one another.

Later I may add telescopic limiting magnitudes figured for a specific exit pupil size (telescopic aperture divided by magnification) to the mix.

I also want to start making better use of filters for the Moon, planets, and deep sky objects; but I think I'm going to need multiple lifetimes in order to accomplish everything!

Happy Birthday Galileo! Galileo Galilei was born on 15 February 1564 in Pisa, Italy. He's known not only for his ground-breaking telescopic observations; but also for his experimental approach that led to the discovery of the pendulum's time-keeping potential, ballistic science, and much more.