✧ What can I see in the night sky tonight? A life list of ten things worth going outside for

Umbriel's free Sky Life List is a field guide to ten things you can actually see with your own eyes or a pair of binoculars: Venus as the evening and the morning star, Jupiter's four moons, Saturn's rings, the Moon beside a planet, a bright star clearing the horizon, a planet standing still, the Moon gone copper in an eclipse, a bite out of the Sun, and a comet. Each night it says which of them are up where you are, and when.

• What you'll needRoughly where you are standing: your device's location, or the place on a chart you have saved
• What you getWhich of the ten sights are above the horizon in the dark tonight from where you are, with times and directions, and a life list that engraves each one with the date and a note once you have seen it
• CostFree, no account required

"What is that bright thing next to the Moon?" is one of the most-asked questions about the sky, and the answer changes every night. The Sky Life List answers it for where you are standing.

It is built around ten sights, chosen because a person without a telescope can really see them: Venus as the evening star, Venus as the morning star, Jupiter's four moons (a steady pair of binoculars shows them as a row of dots), Saturn's rings (a small telescope), the Moon beside a planet, a bright star clearing the horizon, a planet standing still against the stars before it turns, the Moon gone copper in a lunar eclipse, a bite out of the Sun in a solar eclipse, and a comet.

Under today's card, one line says what is out tonight and when, from your own latitude and longitude: which of the ten are above the horizon while the sky is dark, at what time, and in which direction. An object has to be at least 8° up to count, because below that you are looking through trees, roofs and the thickest air.

The page is careful about what it can and cannot know. It knows where things are and whether they are up in the dark, so it always says "could be seen from here": it cannot see your cloud, your streetlights or the hill behind the house. It can say a comet is near the Sun and where it is, but not how bright it will get, because comets are famously unpredictable. For a solar eclipse it checks that the Sun is up where you are, never tells anyone to look at it, and says plainly that looking at the Sun without a proper solar filter hurts your eyes.

Every sight starts as a blank plate. When you see one, tap it, and it is engraved with the date and whatever you want to note. There are no totals and no score: a life list is a record of nights, not a scoreboard, and an empty list is a perfectly good list. The whole thing prints as one plate.

Your list stays private, on your device, and if you sign in it syncs end to end encrypted, the same way the journal does. Nothing is posted.

Everything is worked out from your own latitude and longitude. The engine gives each planet's position, and the page converts it to altitude and direction for your sky, advancing local sidereal time from a single chart at the sidereal rate rather than casting a chart for every sample. Planets are held fixed across one night, because they move well under a degree between dusk and dawn; the Moon moves about 13° a day, so it is recomputed at every sample, seen from your actual spot on the Earth's surface rather than from its centre. The dark part of the night runs from dusk to dawn as the Sun sets and rises for your location, and a sight counts as up in the dark only if it clears the stated altitude inside that window. Stations are found by searching the engine for the day a planet's speed changes sign, and the Moon beside a planet by the true angle between them, latitude included, since the Moon can sit five degrees off the ecliptic. The limits are named on the page as well as here: the comet catalogue carries orbits, not brightnesses, so the page can place a comet but not promise it will be bright; the tilt of Saturn's rings needs Saturn's pole, which this engine does not carry, so no angle is printed; and for a solar eclipse the page checks the Sun is above your horizon at the eclipse instant but does not trace the shadow's track, and says so.