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Our May chart shows Bootes with the conspicuous star Arcturus (star 10) high in the S as the Summer Triangle of Vega, Deneb and Altair climbs in the E and Leo descends in the W. The two brightest objects below and to the right of Arcturus are Saturn and Spica in Virgo, with the planet now close to the star Porrima and edging to within 0.3°, less than a Moon's breadth, by the month's end.
Saturn still outshines Spica, but it dims from mag 0.5 to 0.7 in May as it recedes slightly and the ring-tilt decreases to 7°. Look for the Moon below Saturn and alongside Spica on the 14th when a telescope shows the planet's disc and rings to be 19 and 42 arcsec wide respectively.
The other naked-eye planets are about to participate in their most compact grouping for years, though the event will go largely unobserved from Britain. For a day or two around the 11th, Mercury, Venus, Mars and Jupiter lie some 25° E of the Sun and so close together that they could fit into the same field of view in binoculars. From equatorial latitudes, where they are visible low in the dark E sky before dawn, the view should be breathtaking. Seen from Britain, though, all four worlds rise less than 45 minutes before the Sun, and twilight will swamp the spectacle.
It might be worth looking very low in the E a few minutes before sunrise on the 11th when the brilliant Venus, mag -3.9, lies 0.7° below-right of Jupiter (mag -2.1). Mercury, 1.5° below-right of Venus, and Mars, almost 6° to the left, will be too dim at mag 0.3 and 1.3 respectively. By the 29th, Jupiter rises almost 80 minutes before the Sun and stands 6° beneath the slender and earthlit waning Moon.
Eta Aquarids meteors, debris from Halley's Comet, peak in numbers on Friday but don't expect to spot more than a dozen of these swift meteors as they emanate from low down in the E after 03:00 BST. At least they have no moonlight to compete with.
May diary
1st 00h Moon 7° N of Venus.
3rd 08h New moon.
6th Peak of Eta Aquarids meteor shower.
7th 20h Mercury farthest W of Sun (27°).
10th 22h First quarter.
11th 10h Venus 0.6° S of Jupiter.
14th 16h Moon 8° S of Saturn.
17th 12h Full moon.
24th 20h Last quarter.
29th 16h Moon 6° N of Jupiter.
* Times are BST.
