Solsticio hoy, or rather mañana. Tomorrow, June 21, the spinning planet we live on will hurtle through the point in its orbit at which its north pole leans most toward the Sun. Therefore the Sun will appear farthest north in everyone’s sky. For people living north of the equator, the Sun is in the sky longest, and in the middle of the day its rays slant down most steeply through the atmosphere.
The moment of the sol-stitium, “Sun-standing,” before it begins to retreat southward, is 15:01 by Universal Time. This, if clocks were still on standard time, would be 3 PM in Britain, 10 AM in the Eastern zone of North America; it’s an hour earlier in summer clock-twisted time.
Here is one of the eight illustrations in the “Sun, Earth, and Seasons” section of Astronomical Calendar 2023.
For those of us living at far eastern longitudes, the solstice occurs on 22 June.
My references say 0757 or 0758 PDT, i.e. 1457 or 1458 UTC, a difference of just 3 or 4 minutes from Guy’s 1501 UTC. According to the Nautical Almanac, the Sun’s declination will be North 23 degrees 26.3 arcminutes from June 21 0300 UTC until June 22 0300 UTC, so the Sun will really be standing still in declination as measured by a sextant. By linear interpolation this would put the moment of solstice at 1500 UTC, plus or minus less than 30 minutes. The moment of an equinox, on the other hand, can be observed with better than one-minute accuracy.
One thing that I love about celestial navigation is that it is all about useful approximation and having a realistic understanding of the accuracy of your measurements. If you’re close enough to right and you’re paying attention, you’ll probably get where you want to go without hitting any charted hazards.
The differences between such figures may be caused by the depth of the calculations. My subroutine for finding the position of the sun has more 40 lines, based on the supplement to the Astronomical Almanac, later Meeus. Others may be using a different set of terms. I used to “correct” my figures by checking them against the Ast almanac; now it’s arriving too late. It’s a more comfortable policy to trust the results of my own programs, because they can appear in many different places – timetable of events, sections on the bodies, charts…
Actually in clock-twisted America the solstice is an hour later at 10:58am EDT according to the US Naval Observatory.