The Octant Calendar is an astronomic calendar design by Walter Ziobro. I divides the seasonal year into 8 periods, called octants.

The design was first published on 24 August 2013 on the public CALNDR-L mailing list.

This calendar may be useful, when and where one wants to …

  1. divide the year into eighths, because it’s convenient or appropriate.
  2. use base eight units.
  3. divide the the year at seasonal points without choosing either the cardinal seasonal points or the midpoints between them.

It resembles the Celtic wheel of the year. The octants start on the astronomical date of all cardinal and mid points of the four seasons, like eight of the solar terms of the Chinese calendar do. This results in 43 to 48 days per octant. Latin names represent both the astronomic point and the octant that it starts.

Octants (months)
Latin Name Approximate Gregorian Start Solar Longitude Northern Celtic Chinese Term Approximate Length
Equinoctium australe Sep 23 180° Mabon Qiufen 45 d
Incrementum australe Nov 07 225° Samhain Lidong  45 d
Solsticium australe Dec 22 270° Yule Dongzhi  44 d
Decrementum australe Feb 4 315° Imbolc Lichun  45 d
Equinoctium boreale Mar 21 Ostara Chunfen  46 d
Incrementum boreale May 6 45° Beltane Lixia  46 d
Solsticium boreale Jun 21 90° Midsummer Xiazhi  48 d
Decrementum boreale Aug 8 135° Lammas Liqiu  46 d
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