About TrueSky

Every claim on the site aims to carry a label citation, so we can know where ideas are coming from.

What this is

TrueSky is the real sky computed on your own device, and three thousand years of people reading it. Astronomy comes first: what is actually up there, right now, where you are. Astrology is here too, named plainly, in three systems side by side: tropical, sidereal and the real constellations, all placed on the same computed positions.

Putting the two next to each other only works if you can always tell which kind of claim you are reading. That is what the labels are for.

The five labels

COMPUTEDFrom the ephemeris.On the evening of 11 October 2026, when this site was designed, Saturn was 1.26 billion km away; the light we saw had left it 70 minutes before.

DERIVEDArithmetic on computed values. Checkable.From 400 km up, the horizon drops 19.8 degrees, so stars that never rise for you come into view.

DOCUMENTEDA historical fact, with a source.Ptolemy tied the zodiac to the equinox in the second century. The constellations have been drifting off it since.

READINGInside a tradition's own rules.Hellenistic astrologers held Saturn less harmful in a day chart than in a night one.

PLAYMade because it is pleasing. No claim.Saturn and Neptune shared a patch of sky the month this site was designed.

What stays on your device

Everything this site computes, it computes in your browser. The site is a set of files: there is no program on a server that receives what you type, and there are no accounts, no analytics and no cookies.

Your place: The home page starts from a guess based on your device's time zone setting. It never looks at your internet address, so a VPN does not move your sky. You can search for a town, type coordinates, or let your device share its location, which your browser asks you about first. The place is used only on your device, and it is forgotten when you close the page unless you tick Remember, which keeps it in this browser's storage until you untick it.
The one file fetched: The first time you use a town search box, your browser loads the town list from this site. The search itself runs on your device.
Live astronomy: The live astronomy page can look up a town and fetch a cloud forecast from Open-Meteo, only when you click for them. Those requests go from your browser to Open-Meteo and carry the name you typed or your coordinates. If you tick Remember there, the place is kept in this browser's storage, with a button to forget it.
Birth charts: The birth chart page computes the chart on your device. Saving a chart keeps it in this browser's storage. A link to a chart carries the birth details in the part after the # sign, which browsers do not send to any server, but anyone you give the link to can read them.
Light or dark: If you switch the chart page between light and dark, that choice is kept in this browser's storage.
The host: The files are served by Cloudflare Pages, which, like any web host, sees the requests your browser makes for them, including your internet address. This site adds nothing to that.

Credits

Stars: the Hipparcos main catalogue, European Space Agency (1997), from the Strasbourg astronomical data centre (CDS, catalogue I/239).
Sun, Moon and planets: astronomy-engine 2.1.19 by Don Cross, MIT License, checked against NASA JPL's DE421 ephemeris with Skyfield.
Constellation figures: the illustrations of Stellarium's modern sky culture, under the Free Art License. The constellation lines and the stars each figure is pinned to come from the same sky culture, under CC BY-SA 4.0.
Towns: GeoNames, under CC BY 4.0.
Weather on the live astronomy page: Open-Meteo, under CC BY 4.0.
Typefaces: Cormorant Garamond by the Cormorant Project Authors, IBM Plex Sans and IBM Plex Mono by IBM, all under the SIL Open Font License 1.1 (licence, licence, licence), served from this site.