Is the Moon or the Milky Way going to spoil or help my night shoot?
Choose a date and a place to see the moon phase, illumination, age, moonrise and moonset, then a verdict for photographing the Milky Way core that night. A 30 night strip shows the best dates at a glance.
How the tool works
Moon position comes from a standard low precision formula, and illumination comes from the angle between the sun and the moon. Moonrise and moonset are approximate. In testing against a full astronomy library they were within a few minutes, but treat them as good to about 10 minutes. Phase and age are for midnight at the end of the chosen date.
The Milky Way core is the bright centre of our galaxy, at right ascension 17h 45.7m and declination -29 degrees. That is far to the south of the UK, so at Coalville it never climbs above about 8 degrees. This page counts it as visible above 5 degrees. A night is good when there are at least 30 minutes of full darkness (sun more than 18 degrees below the horizon) with the core above 5 degrees and the moon down or under 25 percent lit. Fair allows deep twilight (sun more than 12 degrees down).
Most UK nights come out poor or fair. In summer the sky never gets fully dark, and in spring the core is only up in the hours before dawn. June to August, around midnight and the early hours, is the usual window. The further south you are, the higher the core sits, so Cornwall and Devon give a little more room than Leicestershire. Cloud and light pollution are not included.
Questions
Why is the verdict poor on most nights?
From the UK the galactic core is low in the south and the nights are short in summer. The core is above 5 degrees for only a few hours, and in the months it is highest the sky is still in twilight.
What counts as a good night here?
At least 30 minutes with the sun more than 18 degrees below the horizon, the core above 5 degrees, and the moon either below the horizon or less than 25 percent lit.
How accurate are moonrise and moonset?
They are approximate. The formula is low precision, so allow about 10 minutes either way, and more if hills hide the horizon.
More photography tools: Sunrise and Sunset Calculator · 500 Rule and Star Trail Calculator