Accuracy
How accurate is Space Radar?
Everything drawn is measured, modelled or illustrative, and says which. This page says what each word means and what we do when we are wrong.
The three words
measured A position worked out from a publisher's data of a stated age: a satellite from its orbital elements, a planet from the ephemeris. The age is part of the number, and a card says "Position propagated from elements 6 days old".
modelled Computed from physics or a fitted orbit, with the error measured where we could: a probe's orbit continued from its last published state, the habitable zone of a star, the temperature of a bare ball at some distance.
illustrative A picture built to explain: the spiral of the Milky Way, a procedural satellite shape, the colour of a planet nobody has seen.
The exoplanet rule
Nobody has seen the surface of a planet of another star. What is known is its size, its orbit, sometimes its mass, and by which method it was found. So on every exoplanet page the size, the period and the method are the Archive's (NASA Exoplanet Archive), anything we work out is marked computed, and the picture is an artist's impression: its colour, clouds and land are imagined, said on the page and printed on the share picture. "Habitable zone" is said only for the band we compute (Kopparapu et al. 2014) and always with the word computed; it says where liquid water could be possible on a rocky world's surface, never that anything lives there.
Where a number can be wrong
- A satellite's position is as old as its elements. After a week a low satellite such as the station can be minutes of travel from where the map draws it.
- Distances and sizes are sometimes changed so that a thing can be seen at all (satellites are drawn larger than life); the card or the picture says so.
- Where we could not look, the card says "could not look" or leaves the line out. A guess is never shown as a reading.
When we get it wrong
Tell us with the form for a wrong number, name or position. Getting it right matters more to this project than anything else. There is no separate corrections log yet. What exists is the project's public history: the changelog, which records changes of facts under its fixes, and every commit and issue on GitHub. A page that lists each correction, with its date, is a task for the project, not something to pretend we already have.