免费月相计算器
根据日期预测当前月相和下次满月日期。
Illumination (%)
50.0 %
Illumination (%) vs Days Since New Moon
公式
## Moon Phase Estimation The synodic month (new moon to new moon) averages 29.53 days. ### Illumination Formula **Illumination = (1 - cos(2π × d / 29.53)) / 2** where d = days since last new moon. This gives 0% at new moon, 50% at first/third quarter, and 100% at full moon. Phase names: 0-1.85 days = New, 1.85-7.38 = Waxing Crescent, 7.38 = First Quarter, 7.38-14.76 = Waxing Gibbous, 14.76 = Full, etc.
计算示例
7.38 days after new moon (first quarter).
- 01Phase = 7.38 / 29.53 = 0.250 (25% of cycle)
- 02Illumination = (1 - cos(2π × 0.250)) / 2
- 03= (1 - cos(π/2)) / 2 = (1 - 0) / 2 = 50%
- 04First quarter: half the disc is lit.
常见问题
How do I find when the last new moon was?
Astronomical almanacs and many websites list new moon dates. A recent reference: 2024-01-11 was a new moon. Count days forward from any known new moon.
Why is the cycle 29.53 days, not the orbital period?
The Moon's orbital (sidereal) period is 27.32 days, but the synodic month is longer because Earth also moves around the Sun, so the Moon needs extra time to return to the same Sun-Moon-Earth alignment.
Does this account for libration?
No. This is a simple geometric illumination model. Actual illumination can vary slightly due to the Moon's orbital eccentricity and inclination.