Stargazing in May: Making the most of the moon
The moon has fascinated astronomers, poets, playwrights and many others besides, writes Nigel Henbest
The first weekend of the month is splendidly kicked off by a full moon in our skies, with the kindly face of the “man in the moon” illuminating our late-night coronation festivities.
Although the full moon seems amazingly bright in our night sky, it’s actually a very dull object – as dark as an asphalt road surface. The moon reflects only one-tenth of the sunlight falling on its surface: the Earth’s reflectance is three times higher; while Saturn’s icy moon Enceladus reflects almost 100 per cent of the incoming light. If our companion were as shiny as Enceladus, we’d be dazzled with a moon ten times brighter.
In western tradition, the moon is the beautiful and chaste Diana, goddess of hunting. But in many parts of the world, the moon is a male deity: in Hindu mythology, it was the god Soma, who rides through the sky in a chariot pulled by white horses.
And not everyone sees the pattern in the moon’s disc as a round shining face, with the dark eyes and lop-sided mouth of the “man in the moon. The most common interpretation is the “hare in the moon” – look out for its upright ears at moonrise. Across ancient Europe, people made out the shape of a man carrying a bundle of twigs; while the Chinese saw a three-legged toad silhouetted against the glowing disc.
When astronomers turned the telescope on the moon in the early seventeenth century, they found it was a world rather like the Earth, but very rough and mountainous. The early English astronomer Sir Thomas Lower wrote in 1610 that the full moon "appears like a tarte my cooke made me the last week. Here a vaine of bright stuffe, and there of darke, and so confusedlie al over."
If you’re planning to point your own telescope – or binoculars – towards our neighbour world, it’s natural to think that full moon is the best time to observe it. But hold off! Sunlight is then illuminating the moon’s surface evenly, and there’s little contrast. A few days later the Sun is lighting up the moon obliquely, and dark shadows accentuate the relief. Or wait until later in May, when the moon reappears in the evening sky as a thin crescent, and its shape grows ever broader as it moves towards full moon again in early June.
The moon’s changing phases are also the subject of folklore around the world. According to the Unuit people of Greenland, the Moon is a god – Anningan – who is forever chasing the female Sun around the sky. Anningen is so ardent that he forgets to eat; and grows thinner and thinner. Eventually, he has to come down to Earth to hunt; and the Moon disappears from the sky for three days. When he returns to the heavens, we can see him grow fatter and fatter again.
The truth is of course more prosaic. The moon doesn’t have its own light, and the only part visible is the region illuminated by the Sun. As the moon travels round the Earth, we first see just a sliver of its surface lit up; then more and more, until the moon is opposite to the Sun and we can view the whole hemisphere facing us in the Sun’s glare. Then, we see the illuminated portion shrink, until the moon is so close to the Sun that’s not visible at all.
Before the introduction of artificial lights, the moon was essential for all nocturnal activities. People divided up the year by the coming and going of our natural night-time lantern in the sky: the word “month” actually means “moonth.”
And the moon and its phases figure prominently in past literature. William Shakespeare has Juliet saying to Romeo: “O, swear not by the Moon, the fickle Moon, th’ inconstant Moon, that monthly changes in her circle orb, Lest that thy love prove likewise variable.’
Whatever the phase, we always see the same features on the Moon, because one side permanently faces the Earth. The other side was unknown until the Luna 3 spacecraft sent back images in 1959. Since then, many more robotic missions – and astronauts – have viewed the far side in close up.
But going back a century, when the hidden side of the Moon was a mystery, the English poet Edmund Gosse penned a few lines – not quite in Shakespeare’s league – to express astronomers’ frustration. "Oh Moon, lovely Moon, with thy beautiful face, Careering throughout the boundaries of space, Whenever I see thee I think in my mind, Shall I ever, oh ever, behold thy behind."
What’s Up
Greeting us as the sky begins to darken, Venus is effulgent in the west. This month, the Evening Star remains above the horizon until after midnight. When the moon is out of the way, around the middle of May, choose a location well away from artificial lighting, and see if you spot shadows cast by Venus’s brilliant light.
The crescent moon makes a striking pair with Venus on 22 and 23 May. On 24 May, the moon lies close by Mars, although the “red planet” is currently so far from us that it appears as no more than a brightish star, similar to the twins of Gemini – Castor and Pollux – nearby in the sky.
Overhead, you’ll find the familiar shape of the Plough – the most prominent members of the constellation of Ursa Major, the Great Bear: to the ancient Greeks, the four stars forming a rectangle depicted the ursine body, with three stars marking her tail. Across the Atlantic, these seven stars are seen as the Big Dipper, while schoolkids often nickname it ‘the Saucepan.’
Below the Plough crouches the cat-shaped constellation of Leo (the Lion). Follow the curve of the Great Bear’s tail (the ‘handle’ of the Plough) and you’ll find Arcturus, the leading light in Boötes (the Herdsman), and – further on – the brightest star in Virgo (the Virgin), Spica.
Stay up until the early hours to spot Saturn (rising around 3 am) and giant planet Jupiter, coming up above the horizon about 4 am in the dawn twilight. On the morning of 7 May, you may see some shooting stars of the Eta Aquarid meteor shower, but this year the show is spoilt by bright moonlight.
Diary
5 May, 6.34 pm: Full Moon
7 May, before dawn: Maximum of Eta Aquarid meteor shower; Moon near Antares
12 May, 3.8 pm: Last Quarter Moon
19 May, 4.53 pm: New Moon
22 May: Moon near Venus
23 May: Moon near Venus, Castor and Pollux
24 May: Moon near Mars
26 May: Moon near Regulus
27 May, 4.22 pm: First Quarter Moon
29 May: Mercury at greatest elongation west
31 May: Moon near Spica; Venus near Castor and Pollux
Nigel Henbest’s latest book, ‘Stargazing 2023’ (Philip’s £6.99) is your monthly guide to everything that’s happening in the night sky this year
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