Our celestial neighbourhood in April
PICK OF THE MONTH: Mercury
Best time to see: 29 April, 30 minutes after sunset
Altitude: 13˚
Location: Taurus Direction: West-northwest Features: Phase, surface markings through larger instruments
Recommended equipment: 75mm, or larger
Mercury reaches superior conjunction on 2 April when it appears to line up with the Sun on the far side of its orbit. Consequently, Mercury won’t be visible at the start of April. Its re-emergence into the evening sky is pretty spectacular, the planet appearing bright and distancing itself from the Sun rapidly. On 8 April, Mercury shines at mag. –1.6 and sets 35 minutes after sunset. By 12 April, just four days later, the planet will be setting a full 60 minutes after the Sun, having dimmed a bit to mag. –1.3 by that date.
This pattern continues over the following days, Mercury reaching greatest eastern elongation on 29 April when it will be separated from the Sun by a respectable 20.6˚. On 29 April, Mercury shines at mag. +0.4 and sets 135 minutes after the Sun. On 29 April, Mercury sits 1.3˚ south of the Pleiades open cluster. The Solar System’s innermost planet, Mercury, never appears to wander very far from the Sun in the sky. As a consequence, it appears in the evening or morning twilight rather than against a truly dark sky. If you have a good flat west-northwest to northwest horizon, this will give the best view of Mercury with the Pleiades. As the pair lose altitude the sky will appear darker, but this is countered by the thicker layer of atmosphere we have to look through close to the horizon, causing both objects to appear dimmer.
Venus
Best time to see: 30 April, 30 minutes before sunrise Altitude: 5˚ (low)
Location: Pisces Direction: East Venus is a morning planet but doesn’t rise to a good altitude. At April’s start, mag. –4.2
Venus rises 80 minutes before the Sun; by the month’s end, now at mag. –4.0, it rises an hour before sunrise. Appearing near mag. +1.1 Mars and mag. +0.9 Saturn at the month’s start, Venus appears close to mag. –2.0 Jupiter at the end of the month. If you have a flat east-southeast horizon, on 27 April, it might be possible to catch Venus and Jupiter separated by 3.4˚ with a waning crescent Moon located 4.3˚ below Venus.
On 30 April, Jupiter and Venus appear separated by 41 arcminutes, a figure that drops to 22 arcminutes on 1 May.
Mars
Best time to see: 30 April, 04:00 UT Altitude: 6˚ (low)
Location: Aquarius Direction: East-southeast Mag. +1.0 Mars and +0.9 Saturn converge at the start of April to lie just 19 arcminutes apart on the 5th. Unfortunately, despite rising some 80 minutes before the Sun on this date, their altitude pre-sunrise remains low as seen from the UK.
Fortunately, mag. –4.2 Venus will be on hand to guide the way, Venus appearing 7.3˚ to the left of the fainter pairing as seen from the UK on 5 April.
Jupiter
Best time to see: 30 April, 30 minutes before sunrise Altitude: 5˚ (low)
Location: Pisces Direction: East Jupiter is poorly positioned in the morning sky at April’s start, rising 20 minutes before the Sun on the 1st. By the month’s end, its position improves and the mag. –1.9 planet appears above the eastern horizon, an hour before sunrise.
Saturn
Best time to see: 30 April, 04:00 UT Altitude: 9˚ (low)
Location: Capricornus Direction: Southeast Saturn is a poorly positioned morning planet. On 4 and 5
April, Mars appears close to Saturn, a flat southeast horizon being needed to see this meeting. On the 5th, both planets appear separated by 19 arcminutes, Saturn shining at mag. +0.9 and Mars at +1.0, so well matched. Bright Venus appears 7.3˚ left of the pair as seen from the UK. A waning crescent Moon sits near to Saturn on the mornings of the 24th and 25th. By the month’s end, Saturn remains at mag. +0.9 and despite rising two hours before the Sun, remains low in the dawn twilight.
Uranus
Best time to see: 1 April, 20:40 UT Altitude: 8˚ (low) Location: Aries Direction: West Uranus slips from view, becoming harder to make out against dark skies at a meaningful altitude. Given a flat west-northwest horizon, a slender 6%-lit waxing crescent Moon appears to sit 1.3˚ from Uranus on the 3rd, the altitude of the pair is low as darkness falls, around 6˚.
Neptune
Neptune is a morning planet, but not observable this month.
More ONLINE
Print out observing forms for recording planetary events
The planets in April
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: April
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).
