A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2020 Aug 10, 11:54 -0700
This is an interesting problem of definitions. What do we mean by "time of moonrise today"? Suppose it's a Monday evening, and you're preparing for a night of astrophotography, and you want to make sure you get some Milky Way photos before moonrise. Should you look up the time or moonrise for today or for tomorrow? The right way to do this in the year 2020 is with a simulation app, e.g. Stellarium. Then you won't have any doubts. But suppose you're using a list-based source, like the Nautical Almanac, or a source that interrogates a list. You want to find out when the Moon will rise "tonight". But by this you mean that you want to find out when the Moon will rise before the next sunrise which by standard civil dates is actually parts of two different calendar days. So if it's Monday evening, you need to know when the Moon rises on Tuesday morning, right? But what happens when the time of moonrise is close to midnight? It can get a bit tricky!
You know you can ask a smartphone simple questions. On Android, if you do the "OK Google" thing and ask for the time of sunrise tomorrow, it happily replies with the time. If you ask for the time of moonrise, it punts (at least in my experiment just now) and sends you to some websites. On iOS, Siri obliges with the time of sunrise, no surprise, but it also answers the moonrise question. I haven't experimented enough to see how it handles the near midnight cases.