Comments on: Night of the Great Moon https://habitablezone.com/2012/05/03/night-of-the-great-moon/ Fri, 03 Apr 2026 22:41:18 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: bowser https://habitablezone.com/2012/05/03/night-of-the-great-moon/#comment-14696 bowser Sat, 05 May 2012 18:45:09 +0000 http://habitablezone.com/?p=14614#comment-14696 I wasn't aware of any of that. Interesting, and thanks. This is not a lost day. I wasn’t aware of any of that. Interesting, and thanks. This is not a lost day.

]]> By: ER https://habitablezone.com/2012/05/03/night-of-the-great-moon/#comment-14684 ER Sat, 05 May 2012 00:05:28 +0000 http://habitablezone.com/?p=14614#comment-14684 The illuminated percentage is constantly changing, but the Nautical Almanac gives you that figure too. Although it only breaks it down to the nearest day. The percent the moon is illuminated on May 5, 6, and 7 is 99, 100, and 97, respectively. On those three days, the Almanac gives the semidiameter of the disc as 16.7 minutes of arc. No doubt it varies, but by too small an amount to be of any use for anyone to know it. Needless to say, this type of information is becoming less and less useful to modern mariners with their electronic navigation. I am concerned that it is only a matter of time before the Naval Observatory stops publication of the Almanac, leaving us old salts stranded on the shores of redundancy. Its like shutting down the lighthouses... If you're really anal about it, it is possible to calculate the exact second of full moon because the Almanac gives you both the Greewich Hour Angle of the moon AND sun for every even hour, and a method to interpolate it to the second. GHA is the angular distance of a celestial body from the Greenwich meridian. At full moon difference in GHA equals exactly 180 degrees, by definition. The illuminated percentage is constantly changing, but the Nautical Almanac gives you that figure too. Although it only breaks it down to the nearest day. The percent the moon is illuminated on May 5, 6, and 7 is 99, 100, and 97, respectively. On those three days, the Almanac gives the semidiameter of the disc as 16.7 minutes of arc. No doubt it varies, but by too small an amount to be of any use for anyone to know it.

Needless to say, this type of information is becoming less and less useful to modern mariners with their electronic navigation.
I am concerned that it is only a matter of time before the Naval Observatory stops publication of the Almanac, leaving us old salts stranded on the shores of redundancy.

Its like shutting down the lighthouses…

If you’re really anal about it, it is possible to calculate the exact second of full moon because the Almanac gives you both the Greewich Hour Angle of the moon AND sun for every even hour, and a method to interpolate it to the second. GHA is the angular distance of a celestial body from the Greenwich meridian. At full moon difference in GHA equals exactly 180 degrees, by definition.

]]> By: bowser https://habitablezone.com/2012/05/03/night-of-the-great-moon/#comment-14682 bowser Fri, 04 May 2012 22:47:12 +0000 http://habitablezone.com/?p=14614#comment-14682 So now it's a full, fuller and fullest Moon. Nothing stays the same. So now it’s a full, fuller and fullest Moon. Nothing stays the same.

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