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No account, no cookies, no third-party tracking. Sites, watchlist and settings are stored only in this browser. Our server delivers the app files, keeps short technical access logs with shortened IP addresses and counts page requests without IP addresses; the app sends nothing extra for this.

Privacy Legal notice (Impressum)Open-source licences

Run setup againSite, telescope and weather step by step – as on the first visit.

Device

Field of view and filters decide “fits the frame” and the moon rating.

ZWO Seestar S50 Pro

Field of view 2.45° × 1.38° · 2.30″ per pixel · Filters IR-cut, LP (dual-band)

Sensor and focal-length data from manufacturers' specifications; actual values may differ. Your setup is missing? Use “Own values”.

Minimum altitude

Below this the telescope looks through too much air, haze and city light.

30°

Red light

At the telescope: the whole interface turns red on black and keeps your eyes dark-adapted.

Weather forecast

Clear, cloudy or rain – for the nights ahead at your active site.

Off by default. When switched on, the app asks our server for the forecast of your active site, with coordinates rounded to about 10 km. Our server fetches it from the Norwegian Meteorological Institute and does not pass on your IP address. Privacy

Weather data: MET Norway, CC BY 4.0

Available offline

For the telescope without mobile signal.

Stores the app files in this browser so that it also works without a network. Installing the app on the home screen switches this on automatically. No information about you is stored in this cache.

Transfer data

Sites, horizon lines, watchlist and settings – for example from your Mac to your iPhone.

How What to Image Tonight calculates

An object counts as usable when the sun is more than 12° below the horizon and the object is above the minimum altitude and above your horizon line. Astronomically dark hours (sun below −18°) count fully, twilight hours half. The moon never excludes anything – it lowers the rating: strongly with IR-cut, with an LP filter only when it is bright and close to the object.

All times are in this device's time zone. Sun and moon come from Astronomy Engine and are checked against JPL Horizons (deviation below 0.1°).

All figures are calculated approximations for planning. The weather rating is based on an automated forecast by MET Norway. Clouds, haze, light pollution and local obstructions may be different on site. Never point a telescope or camera at the sun without a certified solar filter.

Data sources and licences

All sources are licensed for commercial use as well. If you reuse data or images, the respective licence applies.

OpenNGC – Mattia Verga, CC BY-SA 4.0NGC, IC and Messier objects. Converted, filtered and combined with names, sizes and the sources below; the resulting object database (/data/catalog.json) is licensed CC BY-SA 4.0 as well.
Wikidata – Wikidata contributors, CC0 1.0Sharpless, Barnard and LBN objects, further names.
HYG Database – David Nash / astronexus, CC BY-SA 4.0Bright and named stars (v4.1). Selected and converted; part of the object database under CC BY-SA 4.0.
JPL Small-Body Database – NASA/JPL-Caltech, public dataOrbital elements of comets and asteroids, retrieved when the app is built.
GeoNames – GeoNames, CC BY 4.0Place list for the place search (towns from 5,000 inhabitants, in Germany, Austria and Switzerland from 1,000), shortened.
MET Norway Locationforecast – Norwegian Meteorological Institute, CC BY 4.0Weather forecast, only when switched on.
Astronomy Engine – Don Cross, MITPositions of sun, moon and planets.
MapLibre GL JS – MapLibre contributors, BSD-3-ClauseMap display.

Example photos: Wikimedia Commons, only under CC0, CC BY 4.0 or CC BY-SA 4.0. Author, licence and source are shown with each image on its object page; the small preview images in the target list link there. The images were resized (previews only scaled down, not cropped); resized CC BY-SA images remain under their licence. Photos by NASA, ESA, ESO, NOIRLab or other institutions do not imply that these institutions endorse this app.

Product names and trademarks such as Seestar and ASI (ZWO), Dwarf (DwarfLab), Vespera and Stellina (Vaonis), Celestron, Sky-Watcher, William Optics, Askar, Takahashi, QHY, Player One, Canon, Nikon and Sony belong to their owners. They are used only to identify devices for which the app calculates fields of view; What to Image Tonight is not affiliated with any of these manufacturers.