A joyful society of birds has gathered in our neighborhood for their rites of spring, and the trees around the feeders are full of travelers, some just arrived, some just about to depart.

The cool weather has kept the winter guest juncos around even as April slips away, but it hasn’t deterred the redwing blackbirds from getting started on their accommodations for the summer. The male redwings arrived from the south more than a month ago, and the females are just now beginning to show up, complaining, I’m sure, about how little has been done by their slacker mates to find a nest site and secure a territory.

For all their full-throated singing at this time of year, inspired by the imperatives of the mating game, all of them have a lot of work ahead: building nests, incubating eggs, feeding ravenous nestlings, and fending off threats from hawks, and raccoons, and even snakes. All of them, that is, except the cowbirds.

Wojtek Rychlik’s multiple-exposure photograph of the analemma made in 2004 at his home in Cascade Colorado.

This year the 13th of April falls on a Friday, and under the special rules of superstition Friday somehow compounds the unlucky properties of the number 13 to make it a date of watchfulness and caution. So we watch where we step: not under a ladder, not in the path of a black cat, not on a crack for the sake of mother’s back. But if you dare, stop for a moment this Friday the 13th, say at noon, and lift your face to the sun to bask in a special solar alignment.

On every day of the year except two, April 13 and August 31, the sun occupies a unique position in the sky at noon. But at noon on April 13 and noon on August 31, the sun will be at the same point in the dome of the sky. It is a phenomenon that almost no one celebrates.

When most of us think of the movement of the sun through the sky, we think of its daily trip from the eastern horizon to the western horizon. That’s because we experience the sun in the continuum of time, which on this spinning planet of ours we measure in days — one spin. But if, like the spinning figure skater, we want to keep our bearings in our dizzying day-to-day relationship to the sun, we should do as the spinning skater does: keep our focus on just one point in the revolution and not on the whole turn.