Orion marches into the W evening twilight this month as Leo reaches the meridian and the Plough stands overhead. Meanwhile, the glorious ringed world Saturn reaches opposition on the 4th and is the sole planet on view during darkness. The others are gathering in the Sun's glare although, as it ends its best evening show of the year, Mercury may still be glimpsed through binoculars low in the W where it shines at mag 1.1 and stands 6° high one hour after sunset tonight.
Saturn, now mag 0.3 and brighter than for 3 years, stands at its closest (1,289m km) at opposition. From low in the E at nightfall, it passes due S 90 minutes after our star map times. The planet stands above-right of Virgo's leading star Spica, and creeps 2° W during April towards the double star Porrima whose components are so close together at present that we need a good telescope and perfect conditions to separate them. However, any telescope at all shows Saturn's rings which span 44 arcsec and have their N face tipped at 9°, falling to 8° by month's end. The rotation-flattened disc is 19 arcsec wide.
The Moon lies to the right of Saturn on the evening of the 16th and below Spica on the following night. Earlier in the month, beginning on the 4th, we enjoy further views of the earthlit crescent Moon in the lower W sky at nightfall. In particular, look for it between the Hyades and the Pleiades in Taurus on the 7th when, with optical aid and provided the sky has darkened enough, we might glimpse the instantaneous disappearance of the 4th mag star 37 Tauri behind the Moon; the occultation occurs at 20:14 as viewed from London and at 20:03 from Edinburgh.
Venus, brilliant at mag -4.0, hugs the ESE to E horizon just before dawn. It stands 5° below the Moon on Thursday and 8° below on April 30 when Mercury, Jupiter and Mars are still hidden in the twilight below and to Venus's left.
April diary
3rd 16h New moon
4th 01h Saturn at opposition
6th 16h Jupiter in conjunction with Sun
7th 20h Moon occults 37 Tauri
9th 21h Mercury in inferior conjunction
11th 13h First quarter
17th 09h Moon 8° S of Saturn; 23h Moon 2.5° S of Spica
18th 04h Full moon
25th 04h Last quarter.
* Times are BST.