The April night sky

Graphic: Finbarr Sheehy

The sky at nightfall at present has Jupiter resplendent in the SE as Orion stands a little lower in the SW, lurching over towards the W where it has all-but-set by our chart times. Those charts plot the Plough overhead, pulled out of shape by the map-projection used, while Jupiter has already crossed the meridian and is on its way to setting in the W before dawn.

Jupiter reached opposition, directly opposite the Sun in the sky, on 8 March and, though it is now receding, it dims only slightly from mag –2.4 to –2.3 during April. Its cloud-belted disc, 42 arcsec wide at mid-month, could hardly be better placed for telescopic study in the evening. Tracking WNW in S Leo, it is close to the Moon on the 17th-18th and itself passes only 7 arcmin NNW of the star Chi Leonis (mag 4.6) on 8 April.

The region of sky to the E of Jupiter, roughly northwards from the “V” of “VIRGO” on our chart, is the so-called Realm of Galaxies. It includes the Virgo cluster of more than 1,000 galaxies that lies some 50 million light years away. More than a dozen of these feature in Messier’s catalogue and are bright enough for amateur-owned telescopes.

Mercury appears in our evening twilight in the WNW over the next few days to shine brightly 6° to the right of the very slender earthlit Moon on the 8th. The Moon, still impressively earthlit, climbs to approach Aldebaran on the evening of the 10th for Britain. Between the 8th and the 26th, Mercury dims from mag –0.9 to 1.8 and stands 8° or higher 40 minutes after sunset during its best evening show of the year.

Mars rises in the SE one hour after our chart times. Already the brightest object low in the S before dawn, it more than doubles in brightness from mag –0.5 to –1.5 as it edges 1.5° E from Scorpius to Ophiuchus, and then back again. Due at opposition on 22 May, it approaches from 118 million to 87 million km during April and swells from 12 to 16 arcsec in diameter. Catch Mars below the Moon on the morning of 25 April.

To the SSE of Mars is Scorpius’ leader Antares while to its left is Saturn, bright and improving from mag 0.4 to 0.2 as it crawls W in Ophiuchus. Saturn is 18 arcsec wide at mid-month, its rings being 40 arcsec across with their N face tipped 26° earthwards.