Our celestial neighbourhood in May
PICK OF THE MONTH: Saturn
Best time to see: 31 May, 03:00 UT
Altitude: 16˚ (low)
Location: Capricornus
Direction: Southeast
Features: Rings, subtle banding on the planet, moons
Recommended equipment: 75mm, or larger
Saturn is a morning planet this month with a low altitude before sunrise. Shining at mag. +0.9 at the month’s start, it brightens marginally by May’s close to reach mag. +0.8. On the morning of 22 May a 57%-lit waning gibbous Moon sits 5.8˚ south of Saturn. By the month’s end, Saturn only attains an altitude of 14˚ before the morning dawn twilight begins to reduce its visibility, but it should be possible to follow it through to an altitude of around 16˚.
Saturn doesn’t handle poor seeing well. The view of the delicate rings, which encircle the planet’s globe, is smeared and smudged if the atmosphere is unstable. A good test for how stable the view is comes in the form of the dark Cassini Division, an apparent gap between the outer A ring and the B ring. Under good seeing the Cassini Division stands out well, and it’s possible to follow it most of the way around the Earth-facing section of the rings. This is easier when they are at maximum tilt towards Earth, which they aren’t at present. In the middle of May, Saturn’s tilt approaches a minimum for the year at around 12.2˚, the north pole being the one tilted towards Earth.
Although views of Saturn from the UK have have suffered from low altitude in recent years the planet will get higher, reaching a peak altitude around 21˚ from central UK under dark skies later this year.
Mercury
Best time to see: 1 May, 30 minutes after sunset
Altitude: 12˚
Location: Taurus
Direction: West-northwest
Following last month’s evening appearance, Mercury remains well placed at the start of May. Shining at mag. +0.7 on the evening of 1 May, it lies 1.9˚ from the Pleiades and sets over 2 hours after the Sun. By the end of May’s first week, Mercury will appear at mag. +1.8, still lingering an impressive 2 hours after sunset before setting.
The planet then dims, reaching mag. +4.0 on 15 May and setting 55 minutes after sunset. It’ll be lost from view earlier than this, about 10 May. Inferior conjunction occurs on the 21st and it returns as a poorly positioned morning object after this date.
Venus
Best time to see: 31 May, 30 minutes before sunrise
Altitude: 6˚ (low)
Location: Pisces
Direction: East
Venus shines at mag. –4.0 at May’s start, visible in the morning sky, rising 1 hour before the Sun. At this time, Venus will appear close to the dimmer but still bright Jupiter. Shining at mag. –2.0, Jupiter will lie 22 arcminutes from Venus on 1 May, visible above a flat eastern horizon from around 50 minutes before local sunrise. The planets separate after 1 May as Venus drifts to the east. On the morning of the 27th, look out for a 10%-lit waning crescent Moon, 1.1˚ southeast of Venus. Again, a flat eastern horizon will be needed to spot this pairing.
Mars
Best time to see: 31 May, 03:00 UT
Altitude: 10˚ (low)
Location: Pisces
Direction: East
Mars is currently in the morning sky. On 1 May, it shines at mag. +0.9 and rises 90 minutes before the Sun. By the time the end of the month arrives, it will have brightened to mag. +0.7 and rises two hours before the Sun. It has a close encounter with mag. –2.1 Jupiter on 28, 29 and 30 May, the planets appearing 37 arcminutes apart on the 29th. A few mornings earlier, on 25 May, look out for a low arrangement of Mars, Jupiter and a 25%-lit waning crescent Moon. By 31 May, through a telescope, Mars will have grown in size to about 6 arcseconds across and shows an 87%-lit gibbous phase.
Jupiter
Best time to see: 31 May, 03:00 UT
Altitude: 10˚ (low)
Location: Pisces
Direction: East
Jupiter is a morning planet, lying 22 arcminutes from mag. –4.0 Venus on 1 May. It will be mag. –2.0 on this date and will be an impressive sight from a flat eastern horizon. View from 40 minutes before sunrise.
Venus departs the scene over the following mornings, but Jupiter isn’t left alone, being joined by Mars towards the month’s end. On the 25th, mag. –2.1 Jupiter, mag. +0.7 Mars and a 25%-lit waning crescent Moon may be seen low above the eastern horizon from around 1 hour before sunrise. Jupiter appears closest to Mars on 29 May, the pair separated by 37 arcminutes.
Not visible this month
Uranus, Neptune
The planets in May
The phase and relative sizes of the planets this month. Each planet is shown with south at the top, to show its orientation through a telescope
Jupiter’s moons: May
Using a small scope you can spot Jupiter’s biggest moons. Their positions change dramatically over the month, as shown on the diagram. The line by each date represents 01:00 BST (00:00 UT).
