A short run of days
Moon Illumination
Moon illumination in this table is the sunlit percent at local noon for each date in a span from 7 to 30 days. Use it to plan photographs or to watch the month change. It is not a fortune table.
These percents are estimates for learning and curiosity. They are not an observatory ephemeris, and they are not a guide for navigation.
How this is calculated
Each row uses the same elongation model as the other tools, once per day at local noon. Illumination is (1 + cos i) / 2. The bars are that percent drawn as a simple width. The series does not include moonrise times or weather.
Questions
Can I use this to plan a night photograph?
You can see whether the near side is a thin crescent or nearly full. You still need a sky forecast, a location, and moonrise data from another source. This table does not provide those.
Why is a quarter day not exactly 50 percent?
The name and the cosine do not stay locked together. A quarter day can read a little above or below 50 percent in this model, and in nature the same thing happens.
Is a higher percent “better energy”?
No. A higher percent only means more of the near side is sunlit. People sometimes tell stories about the moon and mood; that is culture, not a result from this table.
What if I enter 6 days or 40 days?
The calculator asks for 7 to 30 days and will not build a series outside that span.
Whose noon is “local noon”?
Noon on this device, in the time zone set on the computer or phone. The page does not detect New York from your IP. A New York visitor sees Eastern Time only if that is their device zone.