Ancestors

Written by Bob Horowitz on 2025-01-14 at 19:17

The moon, rising directly behind one of the spires of St Paul's Catholic Church. Taken from our side deck.

I always assumed this alignment would occur every 28 days. But doing a little bit of poking around on the internet, it seems Earth's tilt shifts the moon's position in the sky on a 18.6 year cycle.

So don't expect another picture like this for a while.

[#]photography

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Toot

Written by Mike on 2025-01-14 at 19:53

@BobHorowitz It shifts month to month, too, as the ecliptic moves with the seasons

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Descendants

Written by Bob Horowitz on 2025-01-14 at 20:02

@sunumbral I'm not surprised.

It's hard to dig through all of the information about moon positions and find one definitive source about all of the positional changes of the moon. The last reference I read said the 18.6 year shift was due to the sun's gravity, while another one said the shift was caused by a wobble in the Earth's axis. There are better sources about sunrise positional shifts than moonrise's.

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Written by Noe Valley SF on 2025-01-14 at 21:50

@BobHorowitz @sunumbral Have you tried to plug it into PhotoPills to see when it next lines up?

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Written by Bob Horowitz on 2025-01-14 at 21:51

@NoeValleySF @sunumbral I haven't downloaded it to my phone yet, but that'll happen shortly.

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