Gregorian Comparison

Comparison with Gregorian Calendar

The Light Calendar stays close to the Gregorian year while correcting its natural inconsistencies.
Below is an accurate, concise comparison.

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1. Year Length

System	Length
Gregorian	365.2425 days (average)
Light Calendar	365.242189 days (average)

Difference: 0.0003 days ≈ 26 seconds per year — negligible. The Light Calendar remains fully stable relative to the seasons.

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2. Start of the Year

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.

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3. Month Structure

Gregorian

• Irregular lengths (28–31 days)
• No astronomical meaning

Light Calendar

• 12 Light Months (New February → New January)
• Harmonised lengths: 29–31 days
• Leap adjustment in New January

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4. Astronomical Fixpoints

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.

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5. Moon Integration

Gregorian

• No lunar structure
• Requires a separate moon calendar

Light Calendar

• Integrated lunar index M1–M13 (+ optional M0/14)
• A lunar cycle belongs to the year where its full moon occurs

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6. Date Offset Between Systems

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.

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7. Purpose

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.