Fabricate images of the moon's illuminated percent

2021 Oct.

I am switching this repo to public in case it is of use to former users 
of the very fine USNO service which has now been off line for years.
Should they ask I will return this repo to private status.

I have been fetching images from USNO for decades now. But they stop being reliable quite a while ago.

I should give then a break by generating a set once and keeping them. I have looked around and not found anything I like better and most actual photos I like less.

These images I like are synthetic, (no atmosphere or clouds) USNO got data from USGS which may be moved here build a model and raytrace images on demand, this is why you can request images from any time past present or future.

My goal here is to get a regular set of images over one lunar cycle labeled so they may be reused as stunt doubles of other months. Yes. I will lose up to the moment accuracy, wrong slant on the terminator etc, but will gain independence when USNO temporarily (or permanently) goes dark. Also get a lunar cycle labeled by percent which I can use in other projects.

A synodic month is: 29.530588 Days (avg) Multiply by 24.0 is: 708.734112 Hours Multiply by 60.0 is: 42,524.04672 Minutes Multiply by 60.0 is: 2,551,442.8032 Seconds

If I made one hundred images (whole percents only) they would only be meaningfully updated every seven hours or several (3) times a day.

This is overkill in temporal resolution for my use which is to notice if a good day for sidewalk astronomy is coming up soon. Sounds like a plan; 100 images.

Should be able to pick a date and time for a new moon and step through 100 requests 7.08734112 hours apart.

0.08734112 hours times 60.0 is: 5.2404672 minutes 0.2404672 minutes times 60 is: 14.428032 seconds

07:05:14.428032 is the time step

Using the image server at: USNO

API call looks like:

http://api.usno.navy.mil/imagery/moon.png?date=5/28/1900&time=05:13:03.123

For the sake of pointless precision I woulds like to select a month who's actual length is close to the average length of 29.530588 days.

It should not matter which month get a list of new moons for 2018 from:

http://aa.usno.navy.mil/cgi-bin/aa_phases.pl?year=2018&month=1&day=1&nump=50&format=t

make a script newmoon_date_len.awk to find the actual lengths of each month and subtract the length of our "average" month.

- 2018 Jan 17 02:17:00	0.252745
- 2018 Feb 15 21:05:00	0.0992731
- 2018 Mar 17 13:12:00	0.000662    <-- minimium in this set
- 2018 Apr 16 01:57:00	-0.120171
- 2018 May 15 11:48:00	-0.200727
- 2018 Jun 13 19:43:00	-0.235449
- 2018 Jul 13 02:48:00	-0.231977
- 2018 Aug 11 09:58:00	-0.195171
- 2018 Sep 09 18:01:00	-0.123644
- 2018 Oct 09 03:47:00	0.0214953
- 2018 Nov 07 16:02:00	0.106912

Assuming they cache, months from the recent past may be quicker than months in the future.

2018 Mar 17 13:12:00 looks good enough

make a script generate_slices.awk to generate queries against the api check that the last slice time is sane (it within tens of seconds over the month)

Generate images

    mkdir out
    n=0
    for slice in $(./generate_slices.awk); do
        echo ${n} "\t" $slice;
        curl ${slice}>$(printf "out/%03i.png" ${n});
        ((n+=1));
        sleep 3;
    done

Looks good.

100 1024x1024 images

On my page I use 320x320 so, scale a set

first preserve originals and write protect (the mogrify command will overwrite by default)

mkdir moon_320px

 320/1024  == 0.3125

mogrify -scale 0.3125 -path ./moon_320px/ out/*.png

convert -delay 10 -loop 0 out/*.png gif/lunarcycle.gif

Getting a time to sync the image sequence periodicaly is necessary. there are effemeri... lunar phase tables... or ... use pom (phase of the moon) an ancient BSD command then make a hourly cron job ... hourly because it is both easy and below the nyquist limit for 1/100th of a lunar phase. (which means at some point in an image's interval the image should be the correct one)

0 * * * * mooncurrent.sh

pom is available via your favorite package manager and according to the man page ...

 The pom utility displays the current phase of the moon.
 Useful for selecting software completion target dates and
 predicting managerial behavior.

####################################################################

New project

Consider the lunar cycle divided into - 24 as in hours in a day - 28 as in days in a month ~ 4 weeks

In this case instead of realistic images,
I want to end up with outlines or stencils

42,524.04672 Minutes / 24 = 1771.8352 = 29.530588 hours -> 29:31:50.12

42,524.04672 Minutes / 28 = 1518.715954286 = 25.31193 hours -> 25:18:42.96

really want to generate as many slices as I choose ... rewrite generate_slices.awk to accept a steps variable

    mkdir out24
    n=0
    for slice in $(./generate_slices.awk -v "steps=24"); do
        echo ${n} "\t" $slice;
        curl ${slice}>$(printf "out24/%03i.png" ${n});
        ((n+=1));
        sleep 3;
    done

    mkdir out28
    n=0
    for slice in $(./generate_slices.awk -v "steps=28"); do
        echo ${n} "\t" $slice;
        curl ${slice}>$(printf "out28/%03i.png" ${n});
        ((n+=1));
        sleep 3;
    done

all fine & good but USNO has apparently been offline for some months now ...

shop for alternatives

https://www.moonpage.com/index.html

https://www.moongiant.com

https://stardate.org/nightsky/moon

hmmm no obvious replacement.

futz with the 100 images I have as approximates ...

but ultimately with the time-line, materials and tools on hand
just went with drafting simple line cartoons.

note: for a moon a day cartoon/stencil only need the 12 drawings because each side is used and full new are plain circles.

TomConlin/synthetic_lunar_cycle

Fabricate images of the moon's illuminated percent

Generate images

New project