Umbra: Sky Almanac & Alerts

Most people find out about the good nights the next morning, from someone else's photographs.

Umbra is a sky almanac that runs entirely on your phone. It works out what is happening above your head tonight, how dark it will actually get where you are, and whether that adds up to a reason to put a coat on. Then it tells you, once, in the evening, and otherwise leaves you alone.

ONE NUMBER, AND IT SHOWS ITS WORK

Every night is scored out of ten for your place: what is on, how many hours of true darkness you get, what the Moon is doing to them, and whether the good hour is a civilised one. All four components sit on screen next to the score in plain language, so you can disagree with it. A meteor peak from a suburban garden reads differently from the same night at a dark site, and Umbra says so instead of quoting the headline figure.

YOUR SKY, NOT AN AVERAGE ONE

You tell Umbra where you watch from and how dark that sky is. It never asks your phone for your position, and it holds no location permission at all. Everything after that is computed for those coordinates: sunset, the three twilights, moonrise, the window of true darkness, and the faintest star you should be able to see once the Moon is taken into account.

THE YEAR AHEAD, ALREADY WORKED OUT

Meteor shower peaks with the rate you can actually expect. Solar and lunar eclipses with the times, the magnitude and the altitude from where you stand. Planet oppositions, greatest elongations, close conjunctions and the turns of the year. Each one dated for your longitude and judged for your latitude, including the honest verdict that a famous shower is worth nothing from where you live.

IS THE DRIVE WORTH IT

Add the field you sometimes drive to and Umbra puts the two skies side by side for tonight: the score, the sky limit, the hours of darkness, and what the difference is worth in meteors an hour. Some nights that is sixty extra meteors. Some nights you may as well stay in the garden, and it will tell you that too.

A LIFE LIST

Twenty seven things worth seeing once, from a total eclipse to noctilucent clouds to the core of the Milky Way. Log a night in two taps and Umbra attaches the conditions it computed, so the entry remembers what the sky was really like. Everything exports as one JSON file whenever you want it.

RED LIGHT MODE

The whole app in red, so twenty minutes of dark adaptation survive a glance at your phone. It can switch itself on after dusk.

THE ALERT RULE

You set the score at which a night is worth interrupting you. Umbra shows you the best night your sky can reach in the next six weeks, so the bar you set means something. Then it holds to it: at most one notification a day, nothing in the middle of the night, and an eclipse warning three quarters of an hour before it starts.

WHAT IT WILL NOT PRETEND TO DO

It cannot see the weather. There is no forecast in here and clouds remain your problem. It does not track satellites, whose orbits change faster than an offline app can follow. It has no internet permission, so none of that can quietly change later, and anything that needs a live feed from a server is simply not in the app.

FREE, AND COMPLETE

No account, no subscription, no adverts, no analytics, nothing to unlock. Positions come from published astronomical algorithms that ship inside the app, so the whole thing works in a field with no signal, on a plane, or in five years when nobody is maintaining a server.