Friday, August 7, 2009

Penumbral Lunar Eclipse Imaged

At last Full Moon, August 5, (a last iteration of the "mystical" Triple-Eclipse which had serious Astrologers, particularly in India, concerned, as detailed HERE) the Moon's southern hemisphere slid through the northmost edge of Earth's refracted "outer shadow. As the most partial of lunar eclipses are, this one was virtually impossible to detect buy earthbound observers.

Or, as John Walker wrote at Fourmilab's blog "None Dare Call it Reason," or Fourmilog, "the most subtle phenomena in naked eye astronomy is a penumbral lunar eclipse: the Moon does not pass into the region of the Earth's shadow where the Sun is entirely obscured by the Earth, and consequently, although sunlight on some or all of the Moon is partly blocked by the Earth, the visual effect is very difficult to perceive, especially with the logarithmic transfer function of human vision and its inability to make absolute intensity comparisons of events.

"Fortunately, here in the 21st century, although we don't (yet) have ATOMIC SPACE CARS, we do have magnificently linear digital sensors in our cameras, so it seemed entirely plausible to me that I'd be able to capture the ever so slight shading of the Earth's fuzzy shadow on the Moon during the penumbral lunar eclipse of August 6th, 2009.

"So, I set up my Nikon D300 camera and Nikkor 500 mm catadioptric “mirror lens” (you can see them here another context) about an hour before the eclipse was to begin to allow the optics to equilibrate to the ambient temperature. Then, just before the start of the eclipse, I shot a number of photos of the Moon with various exposure times..."

The Result is excellent, though Mr. Walker almost apologizes for not having corrected for "an apparent rotation," what he has captured is the Moon's fast-moving librational wobble.

It's worth a look, and he has allowed access to a large version by clicking on the version posted to the blog.

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