Eclipses, Moon Phases and Seasons

Hermetic Systems

Windows software to calculate exact times of solar and lunar eclipses,
moon phases, equinoxes, solstices and the solar cross-quarter days
(Imbolc, Beltane, Lughnassad and Samhain)

Download of this program has been temporarily suspended

This program may be used to find the exact dates and times of partial, annular and total solar eclipses, of partial, penumbral and total lunar eclipses (see the screenshot below), of the four main phases of the Moon, and of solstices, equinoxes and solar cross-quarter days (which occur midway between an equinox and its preceding solstice). Moreover, it can do this for any range of years between 1 and 2300. Here is a typical screenshot.

Eclipses, Moon Phases and Seasons screenshot

The following screenshot shows what appears when the Start button is pressed following the calculation using the settings in the screenshot above.

Sample output of 'Eclipses, Moon Phases and Seasons' program

The text file will be found in the location specified via the Output file button (in Explorer, navigate to the target folder then enter the file name, which must have txt extension). When it is loaded into Excel (as a Text File — accept the defaults) and the column widths, etc., are adjusted, it looks like this:

Excel file with output re eclipses etc.

If you prefer event codes rather than the full names then unchecking Long event names will use the codes shown in the box.

IM-TS Imbolc
BE-TS Beltane
LU-TS Lughnasadh
SA-TS Samhain

SPR-EQ Spring equinox
SUM-SO Summer solstice
AUT-EQ Autumn equinox
WIN-SO Winter solstice

DM Dark Moon
1QM 1st quarter moon
FM Full moon
3QM 3rd quarter moon

PELE Penumbral lunar eclipse
PALE Partial lunar eclipse
TOLE Total lunar eclipse
PASE Partial solar eclipse
ANSE Annular solar eclipse
TOSE Total solar eclipse
Eclipses, Moon Phases and Seasons gives eclipse dates in both the Common Era (a.k.a. Gregorian) Calendar (CE) and the Julian Calendar (JC) — or more exactly, in the proleptic versions of these (which allow dates prior to the historical date of first use of the calendar).

For an explanation of the concept of the chronological Julian Date, and its relation to the more well-known concept of the astronomical Julian Date, see here.

Some web pages (in particular, those of Fred Espenak) give eclipse dates using a calendar-switch-over, according to which the dates of eclipses occurring after the date of the official introduction of the Gregorian Calendar (October 15, 1582) are given in the Gregorian Calendar, and dates of eclipses occurring before this date are given in the Julian Calendar — sometimes with no indication of which calendar is being used. Thus if comparing eclipse dates given by this software with dates available on other websites one must be careful as to whether the dates given on those websites are in the Gregorian Calendar or in the Julian Calendar (and don't forget about astronomical year numbering).

The Common Era calendar dates of the four Celtic festivals change slowly (by up to four days) during the years 1-2300 CE. However, during the years 2020-2050 CE:
Imbolc always occurs on the 3rd or 4th of February
Beltane always occurs on the 4th or 5th of May
Lughnasadh always occurs on the 6th or 7th of August
Samhain always occurs on the 6th or 7th of November

This program implements the same astronomical algorithms as our earlier program Equinoxes, Solstices and Cross-Quarter Days. For the solar cross-quarter days (Imbolc, etc.) the date is calculated using the 'true sun' method (not the 'mean sun'). For an explanation of the difference between 'mean sun' and 'true sun' methods, and for comments on the solar cross-quarter days and the seasons, please see the documentation for that program here.

Our later program Celtic Festival and Cross-Quarter Dates calculates the dates of Imbolc, etc., using the definitions of the solar cross-quarter dates (using 'true sun') and the true Celtic festival dates. For further details see here.