THIS MONTH’S PLANETS

This observing period offers the opportunity to see an ice giant with the unaided eye

Uranus is a truly fascinating world – a slow-moving, faraway ‘ice giant’ planet much larger and colder than our own lush, green Earth. Because it’s so faint, many amateur astronomers and skywatchers have never actually seen it themselves, but this month you will be able to find it very easily in the sky because it will be snuggled up close to one of the brightest planets visible in the sky: Jupiter.

At the start of our observing period you’ll find the planetary pair low in the west after sunset, just below the well-known and beautiful Pleiades star cluster, also called the ‘Seven Sisters’. They’ll set two hours after the Sun. You won’t be able to see Uranus very clearly with your eye – even if you are blessed with very dark skies above you – you’ll need binoculars or a small telescope to pick it out of the sky.

The pair will be closest together after sunset on 20 April, when they will be less than half a degree apart – or the width of the full Moon – which is so close together that both will fit in the same binocular field of view. But they’ll look very different: Jupiter will look like a very bright blue-white ‘star’, while Uranus will look like a much fainter, green-hued ‘star’ to its upper right.

As you look at the planetary pair, consider just how far away Uranus is. It is so far from the Sun that it takes 84 Earth years to orbit once around the star, and when we see it we are looking at it as it was two-and-ahalf hours earlier…

After the 20th the pair will move apart and this very rare close encounter of the planetary kind will be over, but it will still be interesting seeing the two very distant, very different worlds so close together. By 1 May Uranus will be two degrees away from Jupiter, down to its lower right. But you won’t have long to look for this faraway world, as by then it will be setting barely an hour after the Sun, and Uranus will be so faint it may well be lost in the twilight glow even earlier than that. Soon after this Uranus will be so close to the Sun that it just won’t be visible, and we’ll lose it from our skies for a while.

Constellation: Pisces Magnitude: +1.4 AM/PM: AM At the start of our observing period Mercury will be a morning object, but it will be rising at the same time as the Sun so won’t be visible. By 15 May its visibility won’t have improved much – its magnitude will have increased, but it will still be rising just 15 minutes before the Sun, washed out of the sky by its glare.

Constellation: Aries Magnitude: -3.9 AM/PM: AM This month Venus will be very hard to see because it will always be close to the Sun in the sky and drowned out by it, even with a magnitude of almost -4.0. At the start of our observing period Venus will be rising at the same time as the Sun, and as the days pass it will move ever closer to it until it is lost in the Sun’s glare.

Constellation: Pisces Magnitude: +1.1 AM/PM: AM At the start of our observing period Mars will be a morning object close to Saturn, but it will be rising just half an hour before the Sun, making it very hard to see in the bright morning twilight. As the days pass Mars will appear to pull away from Saturn and its visibility will improve, but only slightly.

Constellation: Aries Magnitude: -2.0 AM/PM: PM Jupiter is already low in the west at sunset and drops quickly towards the horizon as the sky darkens. At the start of our observing period you’ll spot it in the evening twilight low in the west, just beneath the Pleiades star cluster. It will set two hours after the Sun. However, as the days pass Jupiter’s visibility will deteriorate.

Constellation: Aquarius Magnitude: +1.2 AM/PM: AM This month Saturn will be a morning object, hard to see as it will rise only a short time before the Sun and will be so low in the sky that any trees, buildings or hills will block it from view. At the start of our observing period it will rise just 30 minutes before sunrise, and even by mid-May it will only be rising an hour before the Sun.

Constellation: Pisces Magnitude: +7.9 AM/PM: AM This month Neptune will be a morning object, but at the start of our observing period will rise just 15 minutes before the Sun and won’t be visible. However, its visibility will improve as the days pass, and by 15 May it will be rising more than an hour before sunrise, so will be worth looking for with a telescope.