The moons of Jupiter
January 3, 2012
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Last night, Jane opened our front door and, ignoring the blast of freezing-cold air which blew through the hallway, she pointed up at the night sky. She was pointing to a bright, silvery-white object close to the Moon. If you imagine the Moon as the centre of a clock-face, this object was at about 7 o’clock. Jane focussed a pair of binoculars on this object and then handed them to me. It took me a while to discover that I got a better view without my spectacles on but, when I eventually could see what she had seen, I witnessed a sight which had caused an astronomical revolution in January 1610. The planet Jupiter was visible as a small disc and, in a straight line across the disc were three or four smaller objects. These were the Galilean moons of Jupiter.
When Galileo first observed them, he thought they were distant stars, but he then saw that, while Jupiter appeared to remain still, these smaller objects periodically disappeared and reappeared. He deduced that they were orbiting around Jupiter. This smashed the Aristotelian theory of the solar system, which held that all heavenly bodies orbited around the Earth.
The binoculars had cost Jane about GBP 60. That seems a very reasonable price in order to re-live cosmological and theological havoc.
She also has an app for her iPad (I think it is called ‘Star Walk’) which displays a star map for whichever section of the sky the iPad’s camera can see, with labels for the more prominent objects. This is very useful, particularly when trying to observe the planets.
The phrase “light pollution” has now entered our household vocabulary.