About UULKA

Last updated 6 Oct 2026

UULKA answers one question as clearly as possible: is tonight good for stargazing where I am? It gives every night a score from 0 to 100, shows the best window to look, and explains in plain English what is helping or hurting: cloud, moonlight, humidity and haze.

What you get

• A score for tonight and the next seven nights, anywhere in the world.
• The best viewing window, key times (darkness, moonrise and moonset, the Milky Way core, meteor showers) and an hour-by-hour strip.
• A night planner showing when the Moon, planets, the Milky Way core and showpiece deep-sky objects are highest.
• A live Overhead dome and an interactive Sky chart of stars, constellations, planets, the Moon and satellites; an Earth globe with the day and night line and satellites by group.
• Listen, a generative soundscape made from tonight's sky; a space Feed; Radio with NASA's live Deep Space Network; and a Lab of small tools.
• A night-vision red mode that keeps your eyes dark-adapted, a light theme, and your choice of units.

Where the data comes from

• Weather forecasts: MET Norway (Locationforecast), licensed under CC BY 4.0. We convert and combine the values into a score, so the result is our processing of the data, not MET Norway's own product.
• Sun, Moon and planet positions: calculated on our own server with Astronomy Engine by Don Cross (MIT licence). No sky data is fetched from anywhere.
• City names and coordinates: GeoNames (CC BY 4.0).
• Aurora outlook: the Kp forecast from the NOAA Space Weather Prediction Center. The "possible" or "likely" wording is our own interpretation and is not an official NOAA product.
• Satellites: orbit data from CelesTrak (refreshed every two hours), propagated in your browser with satellite.js (MIT).
• Stars and constellations: the d3-celestial data files (BSD-3-Clause, Hipparcos star positions); coastlines from Natural Earth (public domain).
• NASA: Deep Space Network status (DSN Now), EPIC Earth images from the DSCOVR spacecraft and, when pictures are NASA's own, the Astronomy Picture of the Day. Space headlines come from the Spaceflight News API; each links to the publisher.
• Time zones: the tz-lookup library (CC0), offline.

See How to read the UULKA score for what each part of the score means, and our editorial policy for how we handle accuracy, corrections and advertising.

Honest limits

Forecasts are estimates. UULKA does not forecast astronomical seeing, does not know about your local horizon or street lighting, and only adjusts for light pollution if you choose a Bortle class yourself. Nights further than about three days away are less certain and are marked as such.

Who runs it

UULKA is built and maintained by Digitallo in New Zealand. It is free to use and is intended to be supported by advertising. Questions, corrections and ideas are welcome: see the contact page.

Third-party software notices

Astronomy Engine (copyright (c) 2019-2023 Don Cross), satellite.js, d3-celestial, d3-geo and other open-source components are used under their own licences; the full notices are in the THIRD_PARTY_NOTICES.md file in the UULKA source repository.