WAVING, VERB: a greeting performed with the hand, directed at another local who can see it. The final clause is under review. The local space agency, NASA, has invited the entire species to wave at Voyager 1, a probe launched in 1977 that now stands one light-day from Terra. A message sent to it departs on one calendar day and arrives on the next, which the locals consider prompt.

The mechanics deserve recording. Participants film themselves waving, transmit the footage to computer networks, and other locals watch it. The probe carries cameras, but they face outward, toward places it has not yet arrived. It has no receiver for goodwill; the wave travels in the opposite direction from the probe entirely. "Voyager will never know we did this," Marlene Okafor, Deputy Coordinator for Public Signal Events, told our embed. "That's what makes it real." A bystander added, unprompted and relieved, "My grandson shot mine in portrait so the probe wouldn't see it sideways."

Our observation took place at a scheduled group wave in a public square. At minute nine, the gathering produced its fourth apology, this one from a woman whose audio equipment had failed; no grievance was recorded. By minute twenty we had tallied sixty-one discrete waves, twelve self-corrections of hair, and one man who rehearsed his wave twice into a pocket mirror beforehand, citing nerves. One child waved directly at the probe, skyward, an error no adult corrected, perhaps because the child aimed at the only participant facing them.

For scale: the probe crossed fifteen billion kilometres on less power than a refrigerator bulb, carrying a golden disc of the species' music for listeners that may never exist. The wave requires one hand, lasts 1.2 seconds on average, and was performed by several locals in formalwear. When the emcee called for a second take because the first "didn't feel big enough," the crowd complied, toward the same sky, harder.

The custom leaves one question it cannot answer about itself: who is the wave for, if the recipient is blind and the witnesses filmed it? WAVING, VERB (field revision): a greeting performed at a departing object, for the benefit of the departing object's audience. Sixty-one waves went out. Zero came back. Attendance was recorded as perfect.