A number of constellations can be seen in the May night sky, with Gemini and Canis Minor setting soon after sunset in the south-west, before paving the way for Leo to hold pride of position. Also rising to prominence in the south-east is Virgo, easily identifiable by its brightest star Spica, which together with Regulus in Leo and Arcturus in Bootes forms the familiar asterism of stars known as the Spring Triangle. As the stars continue their east to west movement across the night sky, in the early hours of the morning the constellations of Libra and Scorpius subsequently come into spectacular view.
Only one meteor shower, the Eta Aquarids, occurs during May, and although up to 40 meteors per hour can be seen from southerly latitudes, that number falls to around 10 meteors per hour from mid-northern latitudes. The Eta Aquarids peak occurs on the 5th, and 6th of the month, with this year’s peak occurring during a New Moon, which will improve the prospects of observing at least a few meteors in the northern hemisphere.
New Moon: May 6th
First Quarter: May 13th
Full Moon: May 21st
Last Quarter: May 29th
One of the 13-14 transits of Mercury across the Sun’s disc to occur during this century can be observed on the 9th of May, weather permitting of course. The path of the transit will start at around 11:00 UT, and depending on your location will last for about 7.5 hours. At first sight, the planet might resemble a small sunspot, but it will be perfectly circular, not have a penumbra, and it will be moving at rapid pace. Moreover, for much of the transit, the planet will cross the Sun’s disc too far from the usual sunspot zone for the planet to be mistaken for a sunspot.
This is the first transit of Mercury to occur since 2006, with the next one not expected until November 11th in 2019. Take note, though, since you will be observing the Sun directly, and so it is vitally important to protect your eyesight with approved filters.
Venus is now approaching a position of superior conjunction with the Sun, and throughout the month will be on our star’s far side, meaning that it will be lost in its glare and therefore not visible during May.
During May, you can find Mars low in Scorpius at about 5 degrees to the northward of Antares, from where you can follow its westward motion as it passes between Beta and Delta Scorpii on its way toward Libra. On the 29th/30th May, Mars will have reached its closest approach to Earth for 11 years, at which point it will shine at magnitude -2.1, which will be equal to that of Jupiter for a few days.
Jupiter is not as bright as it was a month ago, but it still shines brightly at magnitude -2.3 in the south. During the month, its magnitude will decrease to -2.1, and its disc will decrease slightly from 41 seconds of arc, to 37 seconds of arc. The planet also ceases its westward motion on the 9th of the month, so look for the King of the planets below the hindquarters of Leo for the rest of May. Note that Jupiter sets at around 4 AM at the start of the month, but sets progressively earlier as the month wears on.
As May begins, Saturn rises about 30 minutes or so after Mars, with its brightness increasing slightly from +0.2 to 0.0 magnitudes. During the whole of May, Saturn will lie in the constellation Ophiuchus where it will form a triangle with the planet Mars and the star Antares in Scorpius, with the distance between Saturn and Mars increasing from about 8 degrees at the start of May to about 15 degrees by the end of the month. However, the distance between Saturn and Antares will remain fairly constant throughout the whole of May.