Observing planner
Choose what you want to see and when. Every night of the month is scored by how high the target gets while the sky is dark, how long it stays high and how much the Moon gets in the way.
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How the score works
The score is our own simple guide, not a measured quantity. It multiplies three parts: how high the target gets during full darkness (astronomical twilight, or nautical twilight at high latitudes in summer), how many hours it spends more than 20 degrees up in that time, and a moonlight penalty that grows with the Moon’s lit fraction, the time it is up and its closeness to the target. Moonlight barely matters for bright planets, so their penalty is small. A score near 100 means a high target in a long, moonless night. Nights that reach only nautical twilight count for less.
Frequently asked questions
How is the score worked out?
From three things: how high the target is while the sky is dark, how long it stays up in darkness and how bright the Moon is. It is a guide to compare nights, not a measured value.
Does the planner include the weather?
No. Clouds cannot be forecast that far ahead. Check the cloud cover maps for the usual cloudiness of the season, and a weather forecast a day or two before.
What is a good score?
Higher is better. The best nights of the month are marked, and anything near the top of the scale is worth planning for.
Related guides
- How to find planets in the night skyFive planets are easy to see with the naked eye. Here is where to look, when, and how to recognise them.
- Light pollution and dark skies: the Bortle scaleFrom a city centre you can count a few dozen stars. From a truly dark site you can count a few thousand, with the Milky Way bright enough to cast a shadow. The Bortle scale puts a number on the difference.
- Twilight and dark sky: civil, nautical and astronomicalThe sky is fully dark only when the Sun is more than 18° below the horizon. Here is what happens before that.
- Binoculars for stargazing: what to buy and what to look atA pair of 7x50 or 10x50 binoculars shows the craters of the Moon, the moons of Jupiter, dozens of star clusters and the Andromeda Galaxy, for a fraction of the cost of a telescope.