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.
Everything in it
Five tabs, and no dead ends.
Grouped the way the app is. Everything listed here is in the build — nothing is a plan, and nothing opens a screen that says the feature is coming.
Explore
- Sky View — the sky drawn over the live camera, or on its own
- Orbital traffic — everything else switched off, satellites drawn with trails
- Sky Map — the whole visible dome at once
- Search — any planet, star, constellation, deep-sky object, satellite or comet, above the horizon or not
- Object detail — position, rise and set, and a Wikipedia summary with its photograph
- Path on selection — where it has been, dashed, and where it is going, solid
- Sky Time Machine — scrub the clock and watch the sky turn
Tonight
- Tonight score — one number for whether it is worth going out
- Sky Quality — cloud, seeing, transparency, humidity, wind, Moon, darkness and light pollution, each with its source
- Best targets — what is actually up, ranked, for your sky
- Twilight windows — dusk, true darkness, dawn
- Meteor showers — active and upcoming, with radiant and rate
Plan Pro
- Photo Planner — a target's position, times and Moon conditions for a chosen night
- Frame the Shot — live camera overlay showing where the target sits now
- Horizon Scan — record your real skyline so visibility knows about your trees
- Calculators — 500 Rule, NPF, exposure reciprocity, hyperfocal, depth of field, field of view, star trails
- My Gear — camera and lens profiles, and free
Field
- Night vision — the whole app in red, one tap from the screen you hold outside
- Compass — true-north heading, with a figure-eight calibration and a star sight to check it
- Find Object — guided pointing until the target is centred
- Timer — exposure, star trails and an intervalometer
- Ambient audio — original music, with the transport on the screen you are already on
My Sky
- Life list — everything you have found, by category, against what there is to find
- Sky Passport — titles earned for real observing, not for opening the app
- Observation sessions — start one outside, and keep what it recorded
- Missions — tonight's and this week's, generated from your own sky
- Share cards — what you saw, drawn to be worth posting
Camera & tools
- Astro Camera — night-sky presets, point and shoot
- Long exposure and frame stacking Pro — many frames combined, noise down by the square root of the count
- Golden & blue hour — the light for the foreground
- Angular separation — the distance between any two objects
- Rise and set — for anything you can search
- Metric or imperial — throughout, including km/h and mi/h
Free covers the whole sky: every star, planet, constellation and deep-sky object, plus the ISS, Tiangong and Hubble. Pro adds the astrophotography suite, long exposure and stacking, live comet and interstellar-object elements, and the rest of the naked-eye satellite catalogue — the things that are either real engineering or a feed that keeps costing something to serve.
Ground truth
No server knows you were here.
No accounts, no backend, no analytics. Sun and Moon come from Meeus' series, planets from Keplerian elements, satellites from an SGP4 propagator, comets from Kepler, Barker and the hyperbolic solver — all evaluated on the phone, all working in airplane mode.
- 9,096stars bundled
- 110Messier objects
- 88constellations
- 150+satellites tracked
Coming to the App Store for iPhone.
A handful of optional features do reach the network — cloud cover, orbital elements, Wikipedia summaries. Each one is named, with what it receives, on the privacy page.