Free astronomy tools for your city and your night

Every tool on this page starts from the same two facts: where you are standing and what time it is. From those, an ephemeris knows where the Sun, the Moon and the planets stand, and the rest is arithmetic done for your city rather than for the planet in general. Nothing here needs an account, and nothing you type is kept.

Which tool answers which question

• What phase is the Moon tonight, and when does it rise? The moon phase calendar gives the whole month for your city: phase, illumination, moonrise and moonset, and how large the Moon comes out on your lens.
• When can I photograph the Milky Way from here? The Milky Way nights calendar keeps only the nights where the core is up, the sky is dark and the Moon is out of the way.
• When will the sunset line up with my street? The Sun and Moon alignment planner finds the dates for any bearing or landmark, Manhattanhenge included.
• When exactly is the equinox this year? The equinox and solstice dates tool solves the four instants to the minute, with the seasons' lengths and your own longest day.
• Is Mercury retrograde right now? The planet retrograde calendar lists every period of the year, Mercury through Pluto, station to station.
• What colour is the sky over Paris at this moment? The sky colour tool paints it from the Sun's height, with the hex codes.

How they are computed

All of them run on the same ephemerides that space agencies publish, through the Orekit library, on the server, in the moment you ask. There is no table looked up, which is why a date can be given to the minute and why a city a few kilometres away gets a slightly different answer. What none of them know is the weather: they say what the sky would show if it were clear.