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Gregorian Comparison
The Light Calendar stays close to the Gregorian year while correcting its natural inconsistencies.
Below is an accurate, concise comparison.
| System | Length |
|---|---|
| Gregorian | 365.2425 days (average) |
| Light Calendar | 365.2421897 days (average) |
Difference: 0.000310 days ≈ 26–27 seconds per year. This means that the Gregorian calendar drifts by one full day every ~3300 years relative to the actual solar year (the real motion of the Sun). The Light Calendar, by contrast, uses the true astronomical year length (currently ≈365.2421897 days) and therefore remains aligned with the seasons.
| System | Year begins |
|---|---|
| Gregorian | 1 January (historical convention) |
| Light Calendar | 1 New February = midpoint between Winter Solstice and March Equinox (floored to midnight UTC) |
The Light Calendar uses the natural turning point of increasing daylight.
- Irregular lengths (28–31 days)
- Historical distortions overlap astronomical meaning (e.g., Augustus wanted his month to be at least as long as Julius Caesar’s, which is why February ended up with only 28 days. The year begins on January 1 because, in 153 BC, the Roman Senate moved the start of the consular term from March 1 to January 1 in order to install a urgently needed military consul sooner.)
- 12 Light Months (New February → New January)
- Harmonised lengths: 29–31 days
- Leap adjustment in New January
In the Light Calendar, the four solar events always fall on day 16 or 17 of their corresponding Light Months. This is a direct consequence of defining the Light Year to begin at the exact midpoint between Winter Solstice and the March Equinox.
| Solar Event | Light Month Date |
|---|---|
| March Equinox | 16/17 New April |
| Summer Solstice | 16/17 New July |
| September Equinox | 16/17 New October |
| Winter Solstice | 16/17 New January |
This regularity has no equivalent in the Gregorian calendar.
- No lunar structure
- Requires a separate moon calendar
- Integrated lunar index M1–M13 (+ optional M0/14)
- A lunar cycle belongs to the year where its full moon occurs
Typical difference between the two date systems:
- At Light Year start: Light ≈ Gregorian − 2–3 days
- Around mid-year: offset grows to ~5–6 days
- Toward the next New Year: offset returns to ~2–3 days
This is expected because the Light Year aligns to the astronomical midpoint, not fixed civil dates.
The Light Calendar improves:
- coherence of seasons
- month structure
- astronomical alignment
- intuitive meaning in terms of daylight
while staying close enough to the Gregorian system for easy adoption.