Today is May Day, and is known in the Celtic tradition as Beltane, marking the traditional half-way point between the spring equinox and the summer solstice. These mid-points of the seasons are called “cross-quarter days”, as they are exactly between the “quarter days”, marking the beginning of each season.

Today features an event that can’t been seen, but one that has been of interest to astronomers since the earliest observers. Early this morning, the planet Mercury passes between the Earth and the Sun, known as its “inferior conjunction”. The alignment isn’t exact, with Mercury to the upper left of the Sun. Mercury reappears late in the month, but still to close too the Sun.

As the twilight fades by 9:15 PM or so, the waxing Gibbous Moon is escorted across the southern skies by the bright, steely-blue star Spica, located just to its lower right. Spica is diminished by the lunar glare this evening, but regains its composure as the Moon moves away through the rest of the month.