The Astronomical Season Calendar (ASC) is an astronomical calendar invented by Chase Roycroft. The ASC is a purely solar calendar, without any monthly or weekly subdivisions, designed to fix the calendar date of equinox and solstice celebrations.

Design of the Calendar[edit | edit source]

Solar days are numbered from the day of the last equinox or solstice, and four astronomical seasons are grouped into a calendar year, beginning with the Northward equinox, which marks the astronomical beginning of Spring in the Northern hemisphere and Fall in the Southern hemisphere.

Overview of the four seasons
Season Starting Event Northern hemisphere Southern hemisphere
A Northward equinox Spring Fall
B Northern solstice Summer Winter
C Southward equinox Fall Spring
D Southern solstice Winter Summer

Advantages and Disadvantages[edit | edit source]

Because the ASC is based directly on astronomical observations (or calculations), no intercalary days are necessary to keep it synchronized with the equinoctial and solstitial years. Because the year begins with the northward equinox, ASC years correspond well with the years of (tropical) astrology, the Solar Hijri calendar, the Badi calendar, and various ancient calendars. However, because of the eccentricity of earth's orbit, the length of each season will vary from one year to another, and the overall length of the year may change as well since the tropical year is not an integer number of days. Conversion to (modified) Julian day numbers is therefore recommended for determining elapsed time. ASC years will also not align with purely lunar years, or (because of axial precession) with the years of sidereal astrology.

Recommendations[edit | edit source]

The ASC can be used with a variety of epochs, but it is recommended that a year zero be included. Dates can be written with a season letter separating a (signed) four digit year and a two digit day, optionally with a fractional part. As an example: 1924B53.21 would indicate the year 1924 from the epoch, 53.21 days from midnight on the northern solstice.

Full calendar[edit | edit source]

Season A
01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93
Season B
01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93
Season C
01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93
Season D
01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93


External Links[edit | edit source]


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