King of the planets rising

There’s lots to admire about the planet Jupiter, which rises in the evening in late January into February.

It’s the largest body in the solar system, besides the sun of course. About 1,321 Earths could fit within its sphere.

A celestial body this size creates huge gravitational field in space. Its effects reach all the way to our planet from 778 million kilometres away, which can be a good thing. Asteroids and comets headed for the Earth can be deflected out of harm’s way.

On the other hand, this immense gravitational slingshot can fling objects toward us. It all depends from what part of the solar system the comet or asteroid originates. 

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Mars at top left, Jupiter below with nicely arrayed line of moons (bottom up) Callisto, Ganymede, Europe and Io. The star to the far left is HIP54057. I shot this in 2015 through my old Meade refractor. (JOHN MCPHEE)

Besides the grandeur of the planet itself, Jupiter’s array of moons is unparalleled in our system. At last count, 67 bodies were known to orbit the planet.

The four largest  - Callisto, Io, Europa and Ganymede - are known as the Galilean moons, after the Italian astronomer who first documented them using his rudimentary telescope.

Over 400 years later, they remain a favourite target of astronomical observers. In typical backyard telescopes and good quality binoculars, they appear as specks of light lined up on one or both sides of the planet. Sometimes  the moons and/or their shadows can be seen slowly crossing Jupiter's disc, known as transits.  You’ll need a telescope that has a lens or mirror at least 90 millimetres in diameter to observe these events. 

Usually only one moon or one shadow can be seen at a time but occasionally two are visible. Much rarer, usually only once or twice a decade, is a triple transit. Check out Sky and Telescope's calendar of Jovian moon events here. 

Jupiter is the only planet that's prominent in the evening this month. But early birds can catch the sight of all five naked eye planets. From east to west, Mercury, Venus, Saturn, Mars and Jupiter will span the sky at dawn. Mercury will be the toughest to spot low in the east because it's relatively dim and closest to the sun. But this plenitude of planets hasn't happened for a decade so get up early and enjoy the show.