Sunlit Design > The Sun API > Documentation > Solar Day of Year Timescale
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Solar Day of Year Timescale
Range
The Solar Day of Year (SDY) timescale covers just one solar year of 365 days. The SDY timescale is similar to the MJD scale but with the "Year" dropped.
Purpose
Functions that accept SDY time values provide 'least error/ best fit/long term average' values useful for every year in the next century. Click here to learn about how these values calculated. When building a sundial or doing architectural calculations, we wish to build to long term average values rather than to the solar values for one particular year. The SDY timescale provides that ability.
Function
SDY times may be calculated using the sdSDYx function.
Definition
January 1 at 00:00:00 UT is SDY 1.0.
January 2 at 00:00:00 UT is SDY 2.0.
and so on, and
December 31st at 12:59:59.9999 is SDY 365.99999999884259
February 29th is not assigned a day number in the SDY timescale. This is because sundials and architechure is done on the assumption of uniform length years.