Data sources & licenses
SkyGrade combines various weather, astronomy and environmental data to compute easy-to-understand ratings for astrophotography and visual astronomy.
The actual rating, weighting and interpretation of the data is carried out by the purpose-built SkyGrade algorithm. The services listed below provide only raw data or basic information.
Weather data
Open-Meteo
SkyGrade uses weather data from the Open-Meteo API. The Open-Meteo API provides meteorological data from various weather models, including:
- Deutscher Wetterdienst (DWD ICON)
- ECMWF
- NOAA GFS
- other regional weather models
Depending on the location and availability, the most suitable weather model is selected automatically.
Source: open-meteo.com
The weather data is used in accordance with the Open-Meteo terms of use.
Sky images
hips2fits (CDS)
The sky views in the Astrophoto Planner come from the DSS2 color and Pan-STARRS DR1 surveys, retrieved via the hips2fits service of the Centre de Données astronomiques de Strasbourg (CDS).
The images are fetched server-side and cached on skygrade.de – viewing the page creates no connection to CDS.
Source: alasky.cds.unistra.fr
Surveys (DSS2, Pan-STARRS 1)
The image data itself comes from the surveys: DSS2 was produced at the Space Telescope Science Institute (STScI) from photographic plates taken with the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. Pan-STARRS 1 originates from the Institute for Astronomy at the University of Hawaii and its partners. CDS makes these images available through the hips2fits service.
Sources: archive.stsci.edu/dss · panstarrs.stsci.edu
Aladin Lite
The optional interactive view (“Explore interactively”) uses Aladin Lite v3 by CDS, licensed under LGPL-3.0-or-later. It loads only after an explicit click; the library and sky tiles are then loaded directly from CDS.
Source: aladin.cds.unistra.fr
Map rendering
Leaflet
SkyGrade uses Leaflet to display interactive maps.
Leaflet is an open-source JavaScript library under the BSD-2-Clause license.
Source: leafletjs.com
Map data
OpenStreetMap
Map data: © OpenStreetMap contributors
License: Open Database License (ODbL)
Source: openstreetmap.org
Cloud cover map
Natural Earth
Coastlines, land areas, lakes and rivers on the cloud cover map come from Natural Earth (1:10m scale). The data is in the public domain and is stored, pre-processed, on our own server.
Source: naturalearthdata.com
GeoNames
Place names on the map come from the GeoNames database (cities above 15,000 inhabitants), licensed under CC BY 4.0.
Source: geonames.org
The cloud data itself comes from Open-Meteo (see above) and is fetched server-side. The map is drawn in your browser from that data – no connection to a map service is made.
Location search
Nominatim
Nominatim is used to search for cities and postal codes.
Source: nominatim.openstreetmap.org
Seeing forecast
7Timer!
To calculate the seeing rating, SkyGrade uses forecast data from 7Timer!. The seeing data serves as one of several factors within the SkyGrade rating.
Source: 7timer.info
Astronomical calculations
The astronomical calculations within SkyGrade are performed in-house. These include:
- Sunrise and sunset
- Civil, nautical and astronomical twilight
- Duration of astronomical night
- Moon phase
- Moon altitude
- Moonrise and moonset
- Observation window
These calculations are performed locally within SkyGrade and are not obtained via external APIs.
Light pollution
The light pollution rating is based on the Bortle class of the observation location. This can be selected manually or estimated automatically from the location.
For the automatic estimate, SkyGrade uses data from the World Atlas of Artificial Night Sky Brightness (2015). A Bortle class is approximated from the modeled sky brightness. It is a model value (about 1 km resolution) that does not take local shielding, altitude or current conditions into account and can therefore differ from the actual class – it is intended as an adjustable suggestion.
Source: Falchi, F., Cinzano, P., Duriscoe, D. et al. (2016), "The new world atlas of artificial night sky brightness", Science Advances 2, e1600377. Data: GFZ Data Services, doi:10.5880/GFZ.1.4.2016.001. License: CC BY-NC 4.0.
Space weather & aurora
GFZ Potsdam (Kp index)
The current Kp index (planetary geomagnetic activity index) and the Kp forecast (PAGER/SWIFT model) come from the GFZ Helmholtz Centre for Geosciences, Potsdam — the official producer of the Kp index.
Source: kp.gfz-potsdam.de
NOAA SWPC
Additional space-weather data for the aurora page — the Bz magnetic field and solar-wind speed, as well as X-ray solar flares (GOES) — comes from the NOAA Space Weather Prediction Center (SWPC). This data is in the public domain (a work of the U.S. government).
Source: swpc.noaa.gov
NASA DONKI
Information about coronal mass ejections (CMEs) and their estimated arrival at Earth comes from NASA's DONKI database (Space Weather Database Of Notifications, Knowledge, Information).
Source: ccmc.gsfc.nasa.gov/tools/DONKI
SDO (Solar Dynamics Observatory)
The current image of the Sun (193 Ångström) is provided by NASA's Solar Dynamics Observatory (SDO). The images are in the public domain – courtesy of NASA/SDO and the AIA, EVE and HMI science teams.
Source: sdo.gsfc.nasa.gov
Astronomy news
astronews.com
The items on the news page are compiled automatically from the RSS news service of astronews.com. SkyGrade shows only the headline and a short summary with a link to the full original article at the source.
Source: astronews.com
Moon image
NASA / LROC
The Moon photo on the “Moon observation” page is a near-side mosaic from the Lunar Reconnaissance Orbiter Camera (LROC) and is in the public domain (NASA/GSFC/Arizona State University). The current phase is rendered with a computed shadow mask.
Source: Wikimedia Commons (NASA/LROC)
SkyGrade algorithm
The SkyGrade score is an independent development. The rating is not based on the ratings or recommendations of the data sources used. Instead, SkyGrade analyzes numerous weather, astronomy and environmental data and independently computes ratings for:
- Deep-sky astrophotography
- Planetary photography
- Visual astronomy
The weighting of the individual factors is continuously refined and regularly reviewed against practical experience.
Twilight factors
The factors are based on the scientifically established relationships between solar altitude, sky brightness and observation quality. The numerical values were developed specifically for SkyGrade to represent the influence of twilight on different types of observation (deep-sky, visual observation and planets) in a realistic way. They deliberately represent not a scientific measurement model, but a transparent rating model.
Disclaimer
Despite careful processing of all available data, forecasts can naturally differ from the actual conditions. SkyGrade provides decision aids but assumes no liability for the actual observing conditions or the suitability of an observing night.
Trademark notice
All product, brand and service names mentioned are the property of their respective owners and are used solely to describe the data sources used.