March Night Sky

The recent dearth of bright planets in the evening sky is coming to an end as Jupiter reaches opposition on 8 March. It is then at its closest, biggest (44″), and brightest (-2.5), though with Jupiter the more important thing is how well placed it is in the sky; if you can see it at all you always get a good size disc.

You won’t need a star map to find it. Jupiter is the brightest object (apart from the moon)  in the evening sky at the moment, and it rises steadily in the east as the evening progresses, before it culminates due south around midnight, some 40 degrees above the horizon. It shines with a very steady light, quite unlike the twinkling of even a bright star on many nights, and its sheer constancy make it easy to see why the ancients identified Jupiter as a king amongst the planetary gods, even though they cannot have known that it is the largest and most powerful planet in our solar system. Try looking at it with the naked eye for a while, and imagining how they saw it, and what they made of it.

A pair of binoculars will show a very obvious disc, and also some or all of the 4 biggest moons, discovered by Galileo. A telescope will show much more. The moons offer much interest. All 4 are usually in view, but sometimes one or more of them will be behind Jupiter’s disc, or in shadow. Sometimes they are in transit in front of Jupiter (and therefore hard to spot) , or you may see their shadow on Jupiter’s disc. You can look up the times of particular events like this if you want to watch them, but it is also quite fun just to see what they are doing on a particular night. And their orbital periods are so short that you will see obvious changes in their relative positions in the space of just a couple of hours of observing.

And then there is Jupiter’s disc. Any telescope will show the main cloud bands. The amount of detail you see will depend on the size and quality of your telescope, and the seeing  – the steadiness of the column of air you are looking through. There are good and bad “seeing” nights, and they don’t always correspond to the clarity of the sky. But it also varies quite a lot over time. Patient observing over 20 minutes or so, not staring, but giving the eye you normally put to the telescope regular rests, will sometimes give you brief glimpses of great clarity, when suddenly lots of detail pops into view – and then disappears again!

Because Jupiter is so bright, your eyes will lose any dark adaptation when you observe it through a telescope, so I tend to do this at the beginning and/or  end of any observing session.

Finally, we need to make the most of our views of Jupiter over the next few months. Jupiter is now heading below our celestial equator in its 12 year journey around the sun, so for the next 6 years it will be less well placed for those of us in the northern hemisphere to enjoy it.