The summer solstice looms – Sunday, June 21 – but on that day I shall be embarking for an adventure in northwestern Spain, so I must post this in advance.
First, there are interesting sights before the solstice, and the evening of Friday June 19 is the time to start looking.
The Moon comes climbing from the sunset, and on Saturday June 20 it will pass south of Venus and, a bit more than 12 hours later, Jupiter. These events are closer together in time than those of May 21 and 24, the planets having moved closer to each other; they are also closer approaches, especially the Moon-Venus one. However, Jupiter is now only 51 degrees from the Sun, as against 73 in May, so the Moon when passing it is slimmer. The appulse (closest approach) to Venus is at about 8 Universal Time, so the nearest American sunset to it is the one of Friday June 19. The passage by Jupiter, about a degree closer, is at about 21 UT.
Jack Gambino may again tell us about his success in using the Moon as guidepost to spotting Venus and Jupiter in the daytime sky.
(Asteroid Juno is, at magnitude 10.7, far below naked-eye brightness, fainter than it was at its opposition in January and fainter than thousands of stars not shown; I decided to let it stay in the picture only because it happens to be not far from the goddess Juno’s husband Jupiter.)
Now, the solstice. It comes this year on June 21 at about 17 hours UT, which by clocks on summer Daylight Shifting Time is 6 PM in Britain, 1 PM in eastern and 10 AM in western Usamerica.
What the solstice means is that the Earth’s north pole is most tipped toward the Sun.
As seen from Earth, the Sun reaches its northernmost point in its yearly journey around the sky.
Part of the chart for the Sun in Astronomical Calendar 2015. This is the part of the starry sky now obscured for us by the glare of the Sun. The plot is in the ecliptic framework, so that the Sun’s course appears straight, whereas if plotted in equatorial coordinates it would be humped to the north. The smaller circles for the Sun are at true scale, the month-beginning ones are at twice size.
The solstice point is at longitude or right ascension (they coincide here) 90 degrees. And so, according to the old astrological system, the Sun passes at this moment from the third “sign,” Gemini, into the fourth, Cancer.
But in reality, because of the precessional twist of the Earth’s attitude over about two thousand years, the Sun appears a whole constellation further back: it is passing from Taurus into Gemini. The moment when it does this is June 22, 2 UT.
Roughly the same happens at the other places around the sky where the Sun progresses from constellation to constellation – the “roughly” being because the astronomical constellations have irregular shapes, not constant 30-degree widths like the astrological signs. But this is the most interesting of these pairs of events. It is the first at which the difference has begun to be slightly more than one constellation. Briefly, from June 21 17 UT (solstice) to June 22 2 UT (constellation boundary), the Sun is still in Taurus when astrology says it should be in Cancer.
This began to be so in 1990, when the Taurus-Gemin boundary crossing moment overtook the solstice.
I shan’t be back till July 4 (my birthday), so shall probably be late with the news I would then like to bring you about July 5.