Great question! It made me look at the ephemeris, which includes a minute-by-minute description of the moon’s illumination. I use the Carte du Ciel/Sky Chart open source software for my data, and recommend its wonderful night sky software program that is also included in their free download. At any rate, the moment of Full Moon occurs when the moon is exactly opposite the sun in the sky (and if the alignment is perfect, we get a total lunar eclipse), which was at 9:51am, daylight savings time on Halloween. Of course that moment occurred while the moon was invisible from Kansas as it hadn’t yet risen. The typical way the Full Moon is described, however, is not just for that millisecond that it is exactly 180 degrees opposite from the sun, rather it is expanded because for all practical purposes, someone cannot see shadows beginning to form on the edge of the Full moon for a while, even through a telescope, because it is very subtle. The ephemeris says that it takes approximately 19 hours past that exact point of Full Moon before it shifts from 100% illumination to 99% illumination. This means that the moon looked 100% illuminated as late as 3:48am on Sunday, Nov. 1, so they marked that day 100% illuminated even though the exact moment of Full moon was on Halloween. There! Probably way more information than you expected and if you have any more questions, feel free to ask away! Ken Lassman
I love this info-thank you! What is the difference on the moon chart between a full moon and 100% illumination? Thanks, Marsha Buhler
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Great question! It made me look at the ephemeris, which includes a minute-by-minute description of the moon’s illumination. I use the Carte du Ciel/Sky Chart open source software for my data, and recommend its wonderful night sky software program that is also included in their free download. At any rate, the moment of Full Moon occurs when the moon is exactly opposite the sun in the sky (and if the alignment is perfect, we get a total lunar eclipse), which was at 9:51am, daylight savings time on Halloween. Of course that moment occurred while the moon was invisible from Kansas as it hadn’t yet risen. The typical way the Full Moon is described, however, is not just for that millisecond that it is exactly 180 degrees opposite from the sun, rather it is expanded because for all practical purposes, someone cannot see shadows beginning to form on the edge of the Full moon for a while, even through a telescope, because it is very subtle. The ephemeris says that it takes approximately 19 hours past that exact point of Full Moon before it shifts from 100% illumination to 99% illumination. This means that the moon looked 100% illuminated as late as 3:48am on Sunday, Nov. 1, so they marked that day 100% illuminated even though the exact moment of Full moon was on Halloween. There! Probably way more information than you expected and if you have any more questions, feel free to ask away! Ken Lassman
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