ASTRONOMY 101: JUPITER

What’s that really, really bright star slightly south west of overhead (or zenith) at the moment that you can see from all over the Northern Hemisphere at dusk?  Well actually, it’s not a star it’s the solar system gargantuan gas giant planet Jupiter, which is making its presence felt in no uncertain terms at the moment.  Jupiter is nearly large enough to be regarded as a failed star.  It has a similar composition to the Sun that is mainly hydrogen and helium and emits large quantities of radiation.

It’s easy to tell it’s not a star as planets don’t twinkle.  Planets are very close to the Earth in astronomical terms and hence unlike stars aren’t point sources of light, but show proper discs.  If you look at Jupiter with binoculars you'll probably see on either side of it some of its entourage of moons. With a telescope you should be able to make out a couple of dark belts crossing its disc.

These are the planet’s spectacular cloud bands composed mainly of methane and ammonia, impurities in the planet’s immense atmosphere.  Look closely and you’ll see a gigantic red spot, a huge storm that has raged for over four hundred years!

Jupiter as is appears through my Celestron 102SLT refracting telescope. Even at modest magnifications cloud bands in the planet's atmosphere can be clearly seen and sometimes the Great Red Spot too. Also visible even with binoculars are the planet's entourage of Galilean Moons, named after their discoverer Galileo Galilei in 1609.

For the past few years Jupiter has been rather low in the sky, but over the winter  in the northern hemisphere we've been treated to some great views on clear nights, but the planet is starting to set earlier now and the hours of darkness are decreasing, so it's your last chance to get some stunning views of this gargantuan planet.  Jupiter is the third brightest object in the night sky after the Moon and Venus.

Last year a brief bright flash was seen and videoed on Jupiter. This was probably the impact of an asteroid or comet, similar to the impact of Comet Shoemaker-Levy 9 in 1994 which created giant bruises in Jupiter's atmosphere which lasted for months.

But this time, no scars or disturbances were seen. Many astronomers now regard the planet as the solar system’s gigantic hoover, protecting the innermost planets from killer asteroid and comets, and allowing time for life on Earth to evolve.  Sometimes however, these huge rocks from space get through and impact the Earth, such as the one that killed off the dinosaurs!

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