I came across this cool tool which encodes geographic coordinates into 3 dictionary words - table.lamp.chair - for example. You can see their map here https://map.what3words.com/. It divides the world into a grid of 57 trillion 3mx3m squares and each one is assigned with one of these three-word addresses. It made me curious as to whether this sort of thing could work for communicating the locations of stars.

It would be pretty simple to assign unique three-word addresses to stars in stellar databases. What would be even more powerful is if we could encode celestial coordinates into three-word addresses, and create an interactive "what3words" space map. But would this be at all useful?

The finite surface area of the earth allows us to create the grid of 57 trillion squares. Can we work with the infinite nature of the celestial sphere to create something similar?

  • $\begingroup$ The celestial sphere is not infinite: it's absolutely identical to the sphere of the Earth. It is two dimensional. To specify any point on Earth you have a lat and a long. It's exactly the same pointing a telescope at space. Indeed, you could simply use exactly the same scheme for celestial as Earth coordinates! $\endgroup$ – Fattie Jul 18 '16 at 13:15

Possible, yes. In fact since you can just use their algorithm. Sky locations expressed a RA and Dec map directly to coordinates expressed as Longitude and Latitude. The celestial sphere is no more infinite than the terrestrial one.

Each square seems to take about 0.1 arcseconds, which is very accurate, but it does raise a problem: The stars move. Barnards star has proper motion of over 10 arcseconds per year. This is an extreme example, but all the nearby stars move, so their addresses would change. The algorithm is designed not to give nearby locations similar names. So each year Barnards star would have 10 completely different addresses. Other stars would change address due to parallax. If you don't account for precession, all stars would be being renamed all the time.

Now the purpose of the three word addresses is to give addresses to the address-less, in a way that is memorable. Is there a need for addresses of sky locations? We have a cute way of naming larger regions of the sky (the 88 constellations) and stars have names (or catalog numbers) that don't change due to their real or apparent motion. If you need to refer to a location you can use the numeric coordinates.

So: this would not be useful, either for science (since the stars would keep moving address) or for outreach (the Constellations do very well for the whole sky)


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