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My plan was to observe and estimate the apparent magnitude of the Moon during totality of the June 2011 lunar eclipse, but the clouds rolled in at the exact moment, so I couldn't make any useful estimates. What was the apparent magnitude?

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According to NASA on this page, the penumbral magnitude was 2.6868 and the umbral magnitude was 1.6998. I was guessing that that meant magnitudes/arcsec, but the numbers don't make sense to me, whether eclipse magnitudes are listed as actual brightness or change in magnitude. Shouldn't the umbral magnitude be the larger number in either case?

http://eclipse.gsfc.nasa.gov/OH/OHfigures/OH2011-Fig03.pdf

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  • $\begingroup$ The Penumbral and Umbral magnitudes on that PDF aren't referring to brightness but rather to the fraction of the Moon's diameter immersed in the shadow. Since the umbral magnitude is greater than one, the eclipse was total. This wikipedia article en.wikipedia.org/wiki/Magnitude_of_eclipse expains what those values mean and how they are computed. $\endgroup$ – dagorym Jun 21 '11 at 22:47
  • $\begingroup$ Drat! Well, that page has the most information about the eclipse of any I found, even if not the datum that the asker wanted. $\endgroup$ – Andrew Jun 23 '11 at 2:12
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Thank you for the answers! I just received an email from Dr. Richard Keen, turns out the visual magnitude of the eclipse from observers using naked eye, reversed binoculars, and photometry averaged -0.3 and the Danjon L values ranged from 0 to 1.5.

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I was on the wrong side of the planet to see this eclipse, but I would expect it was an extremely dark eclipse, because the Moon passed very close to the centre of the umbral shadow.

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