Sidereo
The sky,
computed.
Every star above you is where Sidereo says it is — worked out on the device, from first principles, with no server to ask. This page runs the same arithmetic.
Move to look around · Drag to take the mount
Point
Whatever you look at, named.
Your cursor is an aperture. Inside it the sky is identified — proper names, magnitudes, distances, the figures the constellations actually make. Outside it, the sky is just the sky. That is the whole of Sidereo, in one gesture.
9,096 stars, from the Yale Bright Star Catalog — the same binary file the iPhone app loads, served here byte for byte.
Time
Scroll, and the night turns.
The sky above is not looping. Scrolling advances the clock, and everything follows from that: the stars swing west, fainter things emerge, the geometry rearranges itself. Sidereo does the same with a slider, so you can find out what tonight looks like at three in the morning without waiting for it.
The wanderers
Planets keep their own time.
Jupiter and Saturn are not painted on. Their positions come from Keplerian orbital elements solved for this instant, which is why they drift against the fixed stars as the hours pass — exactly as they do overhead.
Now you
Find Saturn.
The mount is yours — drag the sky until it is centred. Nothing here will do it for you, which is the point: this is the loop the app is built around, and it is the part that makes you learn the sky instead of reading about it.
In the hand
The same engine, pocket-sized.
These are not screenshots. Each phone runs the astronomy you have been moving through — drag one and it turns with you.
Ground truth
No server knows you were here.
Sidereo has no accounts and no backend. Sun and Moon come from Meeus' series, planets from Keplerian elements, satellites from an SGP4 propagator — all evaluated on the phone, all working in airplane mode.
- 9,096stars bundled
- 88constellations
- 0accounts
- 0analytics SDKs
Coming to the App Store for iPhone.
A handful of optional features do reach the network — weather, aurora conditions, orbital elements, Wikipedia summaries. Each one is named, with what it receives, on the privacy page.