Observatories — how this layer is made

What you are looking at

Each dot is a place where people look at the sky. There are more than 9,000 worldwide. Colour represents which of three kinds it is, and the size of a dot represents the footprint of the site. Click on any of them to see what OpenStreetMap records, such as the institution that runs it and its website. If there's a Wikipedia article, we show a short summary and a link to the full article, in your own language where possible.

Where the data comes from

Every feature here is something a mapper added at the OpenStreetMap website, from a survey, from local knowledge or from aerial imagery. We don't model or estimate anything ourselves, and we haven't merged in any astronomical register.

What we include

Three exact tags:

`man_made=observatory` is the site or the building, and there are more than 3,000 of them.
`man_made=telescope` is a single instrument, one optical tube or one radio dish, and it is the largest class at more than 5,000.
`amenity=planetarium` is a dome that projects the sky for an audience, more than 900 of them. It is a public building rather than an instrument.

Decommissioned instruments and museum pieces are all here, because OpenStreetMap has no reliable tag separating a working telescope from a retired one. Historic observatories that are now only museums are here too. Amateur observatories in gardens appear where somebody mapped them, and so do a few satellite ground stations tagged as telescopes by mappers who read the tag loosely.

Colour

Colour represents which of the three a feature is. The division worth seeing is the instrument against the place, because a swarm of one colour is a single array and a scatter of another is many separate observatories. Planetariums sit apart from both, since they follow cities rather than dark skies.

A count of dots is not a count of observatories

A large radio array is mapped dish by dish. The Very Large Array in New Mexico is twenty-seven features, and MeerKAT in South Africa is sixty-four. The densest view of this layer anywhere on earth is the Karoo in South Africa, where several hundred features sit on one screen and together they are one observatory. A university dome with one telescope inside it may be a single feature, or two, if somebody tagged the building and the instrument separately.

Size

The size of a dot represents the footprint of the feature in square metres. About half are drawn as an outline, and among those a typical one covers about 100 m², which is one dome. The other half are recorded as a bare point with no shape, and we draw those at one nominal small size. The largest single feature is the reserve around the Australian Square Kilometre Array Pathfinder, at more than 25 square kilometres. That is a very wide range, so we set the size scale differently at far and close zoom to keep both ends readable. More than half of the features record a name, and many single dishes inside an array do not, which is why the operator row in the details panel often separates one from its neighbours.

Where the map is empty

An empty area means nobody has mapped an observatory there, and on this layer it often also means there is nothing to map. Professional astronomy is sited where the sky is dark, dry, high and stable, so the instruments gather on a few mountain ranges and deserts, including the Atacama, Hawaii, the Canaries, the Karoo and the Tibetan plateau. Mapping is still thinner across parts of Africa and central Asia than across western Europe.

Up to date, mostly

OpenStreetMap is edited continuously, and we take a new copy once every one to three months. An instrument dismantled some time ago may still be mapped until a mapper updates it.

Source and licence

Back to the map