Objects

How it is organised

Planets and moons are the bodies whose positions come from solar-system orbital elements: Mercury through Neptune, and satellites such as the Moon, Io, Europa, Titan and Triton that you can watch circling their parent in the orbit view. Dwarf planets, asteroids and comets work the same way, though a comet's period can run from decades to millennia, so you have to wind time forward hard to see one complete a lap.

Stars hold essentially fixed positions but rise and set as Earth turns and orbits. The index runs from bright anchors like Sirius and Vega through near neighbours such as Proxima Centauri to supergiants like Betelgeuse and Stephenson 2-18. Deep-sky entries are the objects beyond our own neighbourhood — the Andromeda Galaxy, the Orion Nebula, the Crab — alongside black holes such as Sagittarius A* and M87*. All 88 constellations are here too, each with its figure stars, its mythology and a note on how to find it.

Spacecraft are a special case. Probes still flying — Voyager 1 and 2, New Horizons, Parker Solar Probe — appear at their current position along a real trajectory in the orbit view. Finished missions such as Cassini, and craft still awaiting launch, are included with their planned paths.

How far to trust the numbers

The figures are representative values compiled from NASA and IAU material. Well-established quantities such as diameters and orbital periods are simply rounded; distances, which depend on method, use widely cited numbers. Uncertainty grows with distance — parallax pins nearby stars to within a few percent, while published distances to nebulae and galaxies thousands of light-years away can differ by tens of percent. A few entries, such as the radii quoted for hypergiants like UY Scuti and Stephenson 2-18, have shifted as observations improved.

The same caution applies to the simulated positions. The engine works from J2000 mean orbital elements, which matches what you see with the naked eye but is not survey-grade. Where seconds matter — eclipse contact times, for instance — check an official prediction as well. Every page carries a note to that effect at the foot.