March

Ancient craters and more youthful formations alike tell a tale of lunar geological history, writes Mark Armstrong.

An evening Jupiter is the dominant planet, though brilliant Venus is an improving evening ‘star’. There’s a chance to spot a very young Moon, while we explore early spring’s diverse deep sky.

Observe a young Moon

When : 19 March.

What’s special : We all love to see a thin crescent Moon set against a crystal clear early evening or morning twilit sky. This month, however, there is a special observational feat to go for at around sunset by attempting to view the Moon’s gossamer thin crescent in the hours after the instant of New Moon, which occurs at 01:23 GMT/UT.

How to observe : The spring months of March and April are best to spot a very young Moon, when the angle the ecliptic makes with the local horizon, a crucial factor, at mid-northern latitudes is at its steepest.

The Sun sets at 18:11 in London and the Moon, not quite 17 hours old and illuminated by just 0.56 per cent, lies around 7 degrees above (azimuth 286°) the Sun (sunset is at 18:24 in Edinburgh). Eagle-eyed observers peering hard across a perfectly clear and transparent western horizon may have a shot at seeing the Moon without any optical aid. The record for the earliest observation of the Moon at a lunation is held by Stephan James O’Meara at Mount Wilson Observatory, California, when he spotted a 15.6-hour-old crescent on 24 May 1990.

The rest of us mere mortals will probably have to settle for a view through a pair of binoculars or a small telescope, especially if transparency is compromised by atmospheric conditions. Before you sweep along the horizon you need to be absolutely sure the Sun has set or is hidden by a rigid structure until it sets. Even a glimpse of the Sun through an optical instrument can permanently damage your eyesight.

Venus returns

When : Soon after sunset.

What’s special : Venus, the brightest planet in the Solar System and a dazzling jewel to behold, enriches in no small way the planetary scene when it is on show as a morning or evening ‘star’. This month Venus makes its very welcome return to the night sky as the latter, emerging from superior conjunction on the far side of the Sun in early January. It is now on the long road to greatest eastern elongation from the Sun, on 15 August.

How to observe : Venus makes steady rather than spectacular strides in accessibility. If you have an uninterrupted view of a clear western horizon, the planet’s brilliance (holding at magnitude –3.9 throughout the month) makes it an easy and unmistakable sight.

At the start of March, Venus can be seen around five degrees high at the end of civil twilight (when the Sun lies six degrees below the horizon), timed at 18:14 and 18:25 for London and Edinburgh, respectively. A fast waning Saturn (in conjunction with the Sun on the 25th) lies within a degree of Venus soon after sunset on the 8th; a pair of binoculars should show the conjunction in good conditions, but be sure the Sun has set before observing. Easier to see should be the slim crescent of a young Moon above Venus on the early evening of the 20th.

Venus’ situation is much improved by the end of the month. The brilliant planet now lies some 11 degrees high (hold your clenched fist sideways at arms length and the distance across your knuckles is about 10 degrees) for the same degrees of twilight, at 20:05 and 20:27 BST in London and Edinburgh, respectively. A small telescope reveals Venus’ 94 per cent-illuminated gibbous disc.

Jupiter remains dominant

When : evening sky all-month

What’s special : Jupiter is by far the most observer friendly planet, with its brightness and large apparent diameter enabling rewarding and scientifically valuable views of its turbulent cloud-tops. Even a small- to moderate-aperture telescope will reveal Jupiter’s main dark belts and zones and follow the perpetual orbital motion of its four large Galilean moons.

Throughout March Jupiter is well placed in Gemini and, although now two months or so past opposition, still offers about a four-hour observing window at the end of the month.

How to observe : Jupiter burns brightly throughout March, despite fading from magnitude –2.48 to –2.27. It reaches its second stationary point in Gemini on the 11th, appearing anchored in mid-constellation west of the twins Castor and Pollux, some 3.8 degrees north-west of Wasat (delta Gem). At mid-month Jupiter lies due south (culminates) shortly after nightfall (from London at 19:30 GMT), at a very advantageous altitude in excess of 60 degrees. It lies in excess of 30 degrees until just after midnight.

At mid-evening on 17 March there is a good Galilean moon event when Io precedes its shadow in transit and is joined by a relatively rare transit of Callisto, Jupiter’s second largest moon after Ganymede.

Bright star Regulus hidden by the Moon

When : 29 March around sunset

How to observe : Regulus, the magnitude +1.36 leader of the mighty spring constellation of Leo, is occulted on 29 March by an 89 per cent-illuminated waxing gibbous Moon that is rising in the eastern sky. Regulus is one of a number of bright stars, including Aldebaran, in Taurus, and Spica, in Virgo, lying close to the ecliptic (the Sun’s apparent path across the sky to which the planets and, to a lesser extent, the Moon keep to), that are often in the Moon’s direct path.

Such occultations are truly spectacular to observe through binoculars or a telescope of any aperture, especially when the star winks out at the Moon’s dark limb, as is the case here. The only fly in the ointment is that Regulus is engulfed by the Moon about 15 to 20 minutes before the Sun sets, though a telescope at least should still give a good view.

From London, Regulus moves behind the dark limb at 19:14 BST (daylight saving time started at 01:00), with the pair at a healthy altitude of 32 degrees in the east-southeast. In Edinburgh, the occultation is timed for 19:18 BST. Regulus reappears in twilit skies at the bright lunar limb at 20:15 and 20:21 from Edinburgh and London, respectively, with the Sun five and eight degrees down, respectively.

CRATERS down the eons

Ancient craters and more youthful formations alike tell a tale of lunar geological history, writes Mark Armstrong.