National Astronomy Week marks fine show by Jupiter

Early 2014 is a great time to be an amateur astronomer in the UK. Just a few weeks after the BBC’s Stargazing Live TV programmes in early January, we had the annual two-day AstroFest jamboree in February. Now March will open with National Astronomy Week, a celebration that is held every few years to mark a special event.

A true-colour image of Jupiter from the Cassini spacecraft, on its way to Saturn, shows moon Europa’s shadow cast on the planet’s cloud tops. Credit: NASA

This year, the event runs from 1 – 8 March, and the focus is on Jupiter, the largest of the planets, which is high in the evening sky this spring and giving northern hemisphere observers their best views of it for many years.

Astronomical societies across the UK are joining in to celebrate National Astronomy Week with observing sessions, observatory open nights and meetings. You can see what events are taking place in your area by visiting the NAW website.

From the UK, Jupiter is in Gemini at its most northerly point on the ecliptic, that path through the constellations of the Zodiac through which the planets, Sun and Moon appear to travel. This means that it rises higher above the horizon and, weather permitting, you will get better views through a telescope than when it is low in the sky and shining through more of the murky atmosphere.

Even without a telescope, you cannot fail to spot Jupiter. It shines brilliantly at about magnitude -2, with only the Moon and Venus ever brighter in the night sky. If you don’t have any optical aid other than your eyes, you will find it interesting to follow Jupiter’s changing position in the sky as the weeks go by. The planet takes roughly 12 years to make one orbit of the Sun, so on average crosses one of the constellations in the Zodiac every year.
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A small pair of binoculars will show that Jupiter is a little disc, not a star. Hold them steady, perhaps by leaning against a wall, and you will see up to four starlike points to either side of the brilliant glare of the planet, like a string of beads. These are the four large Galilean moons of Jupiter — Io, Europa, Ganymede and Callisto — named after Galileo who spotted them through his first telescope in 1610.

If you check back as the hours go by, you will see that the pattern made by the moons changes quite quickly as they orbit. They move from one side of Jupiter to the other, and if you see fewer than four, it means one or more will be hidden behind or in front of the planet.

Jupiter is so big that even a small telescope will be enough to reveal some detail. First you might notice that it is not spherical, but is squashed, with the distance between the poles (133,708km) considerably less than its diameter at the equator (142,924km).

You should also be able to see that this gas ball of a planet is striped, with a number of bands and belts of different shades. Large telescopes will show some detail in these bands, driven by the planet’s fast winds. One famous feature that you can see in an amateur telescope is a storm that has been raging for hundreds of years that is called the Great Red Spot.

Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.