February Night Sky

Jupiter comes to opposition on 6 February, on the Cancer/Leo border. At magnitude -2.6 it is unmistakable, and with a disc 45″ wide there is plenty to see. But one of the good things about Jupiter (and, indeed, all the outer planets), is that its distance is so much greater than the variations brought by the Earth’s orbital movements, that if you can see it at all, it will always be of comparable size and brightness. (The varying inclination of Saturn’s rings make that planet a partial exception). Mars, on the other hand, varies from 26″ to 3″ (less than Uranus), and yet even when Mars is so poorly placed for viewing as now, for example, when it is close to the sun in the SW in the evening, and just 4″ wide, many astronomical articles make rather a meal of telling you how to find it. A waste of time, in my view!

The observability downside of the outer planets is that their long orbital periods mean they stay in one place in the sky for a long time. Jupiter is the fastest moving of them, but even then with an orbital period of 12 years, it moves on average through one ecliptic constellation per year. Jupiter is well above the celestial equator this year, but  it is now on a southward trend over the remainder of this decade. Another reason to look at it now!

Any kind of optical aid, including binoculars if held steadily, will show some of Jupiter’s 4 Galilean moons. A telescope will show them strung out, typically on both sides of the disc. Their orbital motion is very rapid, so however they appear when you first observe them, if you look again even a hour or so later you are likely to see changes. And from time to time they pass in front of Jupiter, and/or cast a visible shadow on the planet, or even pass in front of each other. You will need a larger telescope to see these events. Journals such as Astronomy Now give you details as to when they occur.

And then there is the disc itself. Any telescope will reveal the two main cloud bands above and below the equator. A larger telescope may reveal much more, but how much depends on the quality of the “seeing” (the steadiness of the atmosphere), as well as the quality of the instrument. And it will tend to come and go. The best thing to do is to make sure you have a comfortable position at the eyepiece so you can watch for several minutes at a time; on a good night you should get glimpses of greater detail. But don’t expect them to compete with the detailed images  skilled amateurs can produce today! The difference is that you are seeing it for yourself.