We will close out May with a few special events for stargazers. On the evening of Thursday the 22nd Mars will pass between us and Praesepe, the Beehive Cluster, a group of stars in the constellation of Cancer. The planet will appear to pass close to several members of the cluster. Of course, the star cluster, at a distance of about 577 light years, is several million times farther away than Mars, so this is just an alignment from our perspective. The Beehive is a loose accumulation of stars that spans an angle in the sky a few times larger than our Moon. In reality, these stars comprise a galactic or “open” cluster, like the familiar Pleiades, or Seven Sisters that has now entered the daytime sky. These stars were born as a group, bound by gravitation.

The action will be in progress as twilight ends and Mars is about thirty degrees above the horizon, or third the way up the sky, in the west. It will be found bracketed by the bright pair of stars Pollux and Castor to its right and Saturn and the bright star Regulus to its upper left. It is fortunate for us that the bright Moon will not rise until a little before the group sets at about midnight.

The Moon will be a few days after full when our Mars alignment takes place and will be special in its own right. That full Moon, the Flower Moon, on Monday evening, will be the smallest full Moon of the year. The Moon’s orbit is fairly elliptical and this full phase occurs when it is near apogee, the point farthest from the Earth in its orbit. From largest to smallest this variation is only about 10% so is not really noticeable. It is important for solar eclipses, though, since if a solar eclipse occurs near apogee the Moon will appear too small to cover the Sun. That results in an “annular” eclipse, where we still see an annulus, or ring, of the Sun surrounding the Moon.

The night after the Mars passage the Moon passes close to Jupiter, about four Moon-widths away at closest. The pair will be seen to rise together about midnight on the evening of Friday, the 23rd. Mars still stands fairly high in the sky, about half way up in the west, at dark. Saturn is a bit higher, about two-thirds up the sky at twilight. Mercury is very low in the WNW, not quite a fist-width at arm’s length above the horizon in bright evening twilight. Venus is even lower, in the dawn sky and would be difficult to see just before sunrise.