Frequently asked questions

SkyGrade combines weather, astronomy and environmental data into an easy-to-understand value from 0 to 100 and answers one question: is the night worth it? Instead of interpreting raw data yourself, you get a clear rating – separately for deep-sky, planets and visual observation.

Those services show you raw data – you interpret it yourself. SkyGrade does the interpreting and condenses everything into one score, while still showing the individual factors. It is meant as a quick decision aid, not a replacement for a detailed hourly overview.

Both. Beginners get a clear yes/no answer without expert knowledge; advanced observers see all sub-ratings and the exact dark window and can understand why a night is rated the way it is.

Beyond the night rating there are dedicated sections for: Tonight (a compact overview of the night), Planets, visual observation (best targets per equipment), Moon observation, a Moon calendar (dark, moonless nights), Aurora (Kp index & chance) and sky highlights (meteor showers, eclipses) – plus a blog with background articles.

By place name, postal code, a click on the map, or directly as GPS coordinates (latitude, longitude). If a place name occurs more than once (e.g. “Neustadt”), SkyGrade asks which one you mean. GPS entry is especially handy for remote dark sites without a place name.

SkyGrade covers all of Europe (over 40 countries) – with location-accurate light pollution and the time zone valid at your location (all times in local time):

• Central & Western Europe: Germany, Austria, Switzerland, France, Belgium, Netherlands, Luxembourg, Liechtenstein, Monaco, Andorra
• Northern Europe: Denmark, Norway, Sweden, Finland, Estonia, Latvia, Lithuania, Ireland, United Kingdom
• Southern Europe: Italy, Spain, Portugal, Greece, Malta, Cyprus, San Marino, Vatican City
• Central & South-Eastern Europe: Poland, Czechia, Slovakia, Hungary, Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, North Macedonia, Albania, Kosovo, Romania, Bulgaria, Turkey

The Atlantic islands (Canary Islands, Madeira, Azores) are included too. Outside this region SkyGrade cannot (yet) provide a reliable light-pollution estimate.

It is estimated automatically from your location – based on an up-to-date sky-brightness map from 2024 (David Lorenz, night-light data from the Earth Observing Group). That is a model value with about 1 km resolution; you can override it manually at any time if you know your sky better. If a location lies outside the covered map, SkyGrade points this out and assumes a neutral default value.

Because the requirements differ: a night with turbulent air is poor for planets but often still okay for deep-sky. Deep-sky and planets refer to imaging, visual to observing at the eyepiece or with binoculars.

The weather data comes from Open-Meteo (including the DWD ICON model), the seeing from 7Timer. SkyGrade is only as good as the forecast – that is why there is a 7-night preview and an hourly trend, so you can judge the forecast uncertainty yourself.

For deep-sky SkyGrade gives two figures: the realistic deep-sky suitability at your location (including light pollution) and the conditions tonight (the same night, but imagined under a perfectly dark sky). The gap between them is exactly your location’s light-pollution disadvantage – so you can tell at once whether a mediocre rating is due to a bright city sky or to the weather. For deep-sky, light pollution is weighted most heavily because it determines which objects are reachable at all.

Via the Moon's altitude and its actual brightness: a full moon below the horizon does not interfere at all, a full moon high in the sky does so maximally. What counts is not the illuminated fraction but the real brightness – a half moon is only about one eleventh as bright as a full moon, not half. The interference is also coupled to sky darkness – under a dark rural sky the same moon brightens the sky more than in an already bright city. SkyGrade computes the moon position and phase itself from location and date, without any external request.

If the sun does not reach minus 18 degrees, the sky stays lit. SkyGrade then lowers the deep-sky score in steps, while bright targets like planets are barely affected.

Dew forms when the optics get colder than the dew point. Radiating heat to the cold sky, they often cool several degrees below air temperature – most strongly under a clear sky with little wind. Ironically, these astronomically best nights are the most dew-prone. SkyGrade shows you the three key values: low cloud cover, weak wind and a small dew-point spread together mean high dew risk. A dew shield helps, and actively a dew heater.

SkyGrade is free, needs no sign-up and uses no cookies; no user profiles are created. Only coordinates are sent to the weather services for the calculation. Details are on the privacy page.