MOON OBSERVING GUIDE
What does Moon illumination percentage mean?
The illumination value shown by Oh My Luna is the fraction of the Moon’s apparent disk that is sunlit from Earth’s viewpoint. It is not a measurement of how much light the Moon itself produces.
About 0%
Near new Moon
About 50%
Near first or last quarter
About 100%
Near full Moon
Are illumination and phase the same thing?
They are related, but not identical. Illumination is the percentage of the apparent disk that is sunlit. Phase also tells you whether that illuminated fraction is growing or shrinking, so a roughly 50% illuminated first-quarter Moon and last-quarter Moon are different phases.
Does 80% illumination mean it looks 80% as bright?
No. The percentage describes illuminated area, not perceived brightness. Altitude, atmosphere, nearby light and Earth–Moon distance also affect how bright the Moon appears.
Where can I check today's illumination?
The current Moon view shows today’s phase and illuminated fraction. The calendar lets you compare dates, while Tonight adds location-dependent rise, set and direction information.