Does right ascension of the Moon vary significantly enough to calculate it for every particular location?

A very specific question I have an answer to. No it doesn’t.

Using PyEphem in PyLunar (because I am a rebel like that), let’s look at right ascension values through the course of three months for two timezones and a variety of locations.

There is a series of data you want to look at to be sure that you don’t have to make extra effort to solve this.

How I do things

My code is pretty much like this:

import datetime, pylunar

for single_date in ( + datetime.timedelta(n) for n in range(365)):
    _today = datetime.datetime.combine(single_date, datetime.time(16, 0))
    mi = pylunar.MoonInfo(location)
    ra = degree_to_hms(mi.ra())
    fra = float(ra.split()[0] + '.' + ra.split()[1]  + ra.split()[2].split('.')[0])
    print('[%s] %s' % (single_date, fra))

The only function I will leave outside of this is degree_to_hms – it is an algorithm rather easy to find, I have nothing to do with it. You can find it easily.

Within one timezone

So what is going on – I am iterating a year from today and get right ascension. Time is 4pm (16:00) every day. And location is now set to (55, 75), (37, 61) – it is Moscow, my hometown.

October 4th through December 30th, 2020.

It is apparent what is going on – every day right ascension is acquiring 1 hour and +- several minutes.

If we check how do the right ascension change for the same longitude but different latitude – it is a lazy way to emulate how does right ascension vary in different places in the same timezone. Looking at the previous picture, it’s not too hard to guess how things will enfold.

A pretty regular day – right ascension varies from 23.15 to 23.22.

Apprently, most days right ascension will be pretty much the same. But on some days there will be a drastic difference. Pulling out graphics, you will see that at some hours of some days (end of moon cycle, per se) for some locations the Moon has already started the new cycle, and for some it didn’t. So some already have 0 hours something minutes right ascension, and some are still at 23 hours.

Some are in the old cycle (right), others – in the new (left).

So within the timezone things are close, but across the world?

Further experiments lead me to believe that at the same hour, but in different locations at the same time the situation is pretty much the same. For London and for Tokyo at 3pm you will get approximately same numbers.

Right ascension for different location at midnight.

Again, they vary, but not by much.

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