URANUS AND NEPTUNE
They’re two of the most difficult planets to observe, so here’s how to maximise your chances of viewing them
Uranus and Neptune are the hardest planets in the Solar System to see. This is because they are very far away. As the seventh and eighth farthest planets from the Sun, even at their closest points to Earth they are still 2.7 and 4.2 billion kilometres (1.7 and 2.6 billion miles) distant respectively. As a result they are fairly faint and are very small – just a few arcseconds across in the sky. But just because they are hard to see doesn’t mean it’s impossible… you just need to know where to look and with what instruments.
Uranus is the easiest of these two ice giants to spot. At magnitude +5.7 it is theoretically visible to the naked eye, but in practice – with all the light pollution and atmospheric haze around – very few people will see Uranus with just their eyes. Even in binoculars it will just look like a vaguely turquoise star-like point in the night sky. To see the disc of the planet Uranus, observers will need an eight-inch telescope at least, meaning it may be out of range of less wellequipped beginners.
Uranus is a pretty dull planet to look at because there are no swirling bands of storm clouds like there are on Jupiter and its rings are so dark and faint that they will be invisible to amateur astronomers, unlike Saturn’s beautiful rings. You may be able to identify some faint banding in Uranus’ atmosphere, and filters will help you.
Uranus does have moons, but only a handful are visible from your back garden. The easiest are Titania – the biggest of its moons – and Oberon. It will be possible to spot these through a 12-inch telescope. Ariel and Umbriel are closer to Uranus, which makes them much more difficult to see and image, so you’ll need an even larger telescope to do so, which not many people have. If you can see Uranus’ turquoise disc through the telescope and at least two of its moons, congratulate yourself on a job well done.
Observing Neptune is more difficult. At magnitude +7.8 it can only just be seen in binoculars, but is more likely to be visible in a medium-sized telescope, although you probably will not be able to see it as anything more than a small, blue, round object just 2.4 arcseconds across. For comparison, remember that the full Moon is 1,800 arcseconds in diameter. Using a high magnification of 300x will help resolve Neptune’s disc, but don’t expect too much
– if you can see it as anything other than a star-like point, you’ve done a good job.
The planet’s largest moon is Triton, but at magnitude +14 you will need at least a 12-inch telescope, clear skies and lots of luck. It’s often easier to capture Triton in images taken with your equipment instead.