⚳ Asteroid of the day: the real rock the Moon is standing beside, and who it is named for

Umbriel's free Adopt-a-Rock picks one real asteroid a day: the one the Moon is closest to in the sky, from a library of 26,418 named rocks. The card gives its name, what its official naming citation says it is named for, the year it was found and where it is today. You give that name to one small thing in your own day, and over a year the rocks become a bestiary you can print.

• What you'll needOne small thing from your day; no chart and no account
• What you getToday's asteroid with its name, its official naming citation, its discovery year and its place on the ecliptic, a slot to name one small thing after it, and a printable bestiary of every rock you have met
• CostFree, no account required

More than twenty-six thousand asteroids have names, and each name was given for a reason: a scientist, a poet, a town, a cat, a festival, a friend of the discoverer. Almost nobody ever meets them. Adopt-a-Rock introduces you to one a day.

The rock is chosen by the sky, not by a list. Each day it is the named asteroid the Moon is standing closest to at noon Universal Time, found among all 26,418 in Umbriel's library. The card gives its name and number, the year it was discovered, where it sits on the ecliptic today, and what it is named for, taken word for word from the official naming citation held by NASA's Jet Propulsion Laboratory. Where the citation is long, it is cut at a sentence and marked. Where there is no citation, the card says exactly that. Nothing is invented: there is no backstory machine anywhere in the room.

Then the fun part: you name one small thing in your day after it. The kettle. The 8:40 bus. The plant that refuses to die. That is all. The rock and its small thing go into your bestiary, a page for every rock you have met, printable as an engraved plate.

You never meet the same rock twice. Once a rock has had its day it is out of the running for good, and the library is so large that the pool near the Moon never runs dry.

Only today's rock can be adopted, because this is meeting the rock the Moon is with, not keeping a diary. A day you did not stop by is simply no rock in the bestiary. There is no count, no streak and nothing to catch up on; a bestiary of two rocks is as finished as one of 365.

Your bestiary stays private, on your device, and if you sign in it syncs end to end encrypted, the same way the journal does. Nothing is posted.

Finding the named asteroid nearest the Moon needs the position of every one of the 26,418 in the library, which is about 19 MB of orbital elements and not something to send a phone for one card. So the search is done once, ahead of time, by a build tool running the same engine: for each day it computes the Moon at noon Universal Time and every asteroid's position, and records the nearest rock that has not already had a day. Those daily rows are what the card reads. An offline check recomputes rows with the engine to confirm the table is the engine's. The rule that a rock is never used twice is applied across the whole table, and with a library this size the pool near the Moon has never been close to running out; if it ever did, the build would say so and take the nearest unused rock rather than repeat one. The naming citation is JPL's stored text, word for word, cut at a sentence end and marked where it is long. The rock's name is copied into your bestiary when you adopt it, so a rebuilt table can never change a rock you have already met.