A bit of JavaScript to create the Gravitationism Solar and Lunar calendars.

How The Calendar Works

The year is broken up into 8 seasons, based on the position of the earth around the sun:

• Winter (the start of the year)
• Imbolc
• Spring
• Beltane
• Summer
• Lughnasadh
• Autumn
• Samhain

These range from 44-48 days, because the earth moves in an elliptical orbit, so the seasons closer to the aphelion (which occurs about 2 weeks into summer) are a bit longer.

The lunar months go from new moon to new moon. The month that includes the winter solstice is "January", named for the two faced backward/forward looking god of doorways and passages. (When January starts on the winter solstice, this is very auspicious.)

From there, they are named from 1 to 11:

• Primember
• Duember
• Triember
• Fourember
• Pentember
• Sexember
• September
• October
• November
• December
• Elfember
• Lastly, when another month is needed in order for January to contain the winter solstice, the month of Fayember is added. This "leap month" occurs about every 2-3 years.

Because the lunar months don't line up with the year and seasons, they are sort of "extra". Normal time keeping is done with the number of the Gravitationism year (with G0 corresponding roughly to CE 2024), running from one winter solstice to the next. For example, the conventional ISO date 2026-03-13 would be written in its short form as G2-2-38, or long form Friday, G2 Imbolc 38, Day 24 of Duember.

Note that season dates are zero-indexed, and the first day of the season is not given a number, so 2026-06-21 would be G2-5-0 or Sunday, G2 Summer, Day 7 of Sexember.

The included GravitationismDate class is included that will do all the relevant calculations:

import { GravitationismDate } from 'gravitationism-calendar'

// pass in a Date object, or any valid ISO date
console.log(new g.GravitationismDate('2024-06-27T12:00-0700'))
/*
GravitationismDate {
  season: {
    name: 'summer',
    date: 2024-06-20T20:52:00.000Z,
    days: 47,
    gyear: 0
  },
  seasonDate: 7,
  year: 0,
  lunarMonth: {
    name: 'Sexember',
    start: 2024-06-06T12:38:00.000Z,
    end: 2024-07-05T22:57:00.000Z
  },
  lunarDate: 21,
  isoDate: 2024-06-27T19:00:00.000Z,
  fullString: 'Thursday, G0 Summer 7, Day 21 of Sexember',
  shortString: 'G0-5-7'
}
*/

ICS feeds

The ICS feeds are generated for use in the US/Pacific time zone. For convenience, it makes the most sense to align with the solar day, but technically the season doesn't actually start until the moment of orbital alignment, so this can occur on different solar days in different time zones.

If you're in the US/Pacific time zone, and want this data in your calendar app, you can subscribe to these two calendar feeds:

• https://izs.me/solar-events.ics
• https://izs.me/months.ics

To generate the ICS feeds for your time zone if you're not in US/Pacific, run:

npm install
make clean all

and then pull them out of the ./ics folder.