Monday, December 10, 2018

NASA's Dial-A-Moon


It's difficult to get a good photo of the Moon at a small crescent phase. The illuminated area of the Moon - 12% in the photo below, according to a resource from NASA - is small enough that a camera in automatic mode will need to hold its shutter open for a relatively long time, long enough so the image becomes overexposed.

Waxing crescent around 5:10 PM on Monday, December 10, 2018 from Nanticoke
NASA has an amazing resource on its Moon Phase and Libration page called "Dial-A-Moon." This page is year-specific, so the current page is for 2018 only. With Dial-A-Moon, you can specify a date and a time (in UTC time, five hours ahead of Eastern Standard Time, four hours ahead of Eastern Daylight Time) or just let the system default to the current date and time (to the nearest hour.) Here is the Dial-A-Moon visualization for December 10, 2018 at 2200 UTC (5:00 PM Eastern Standard Time):

Visualization from NASA's Dial-A-Moon

Comparing the two images above, you can see that my photograph is "overexposed" relative to the visualization. I had actually cranked the exposure all the way down, and I am very happy with some of the details I was able to capture. But in an effort to make my image more closely match the Dial-A-Moon visualization, I reduced the brightness nearly 50% using Pixlr Editor.

Top image, brightness reduced by about 50%
Now my image more closely matches the Dial-A-Moon visualization. The Moon never presents exactly the same face twice, and when the weather is not favorable, it doesn't present any face at all. Dial-A-Moon lets you see what parts of the Moon are illuminated at any given time. The current version was released on December 18, 2017, so we may be seeing a version for 2019 any day now.

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