Moons of Jupiter. Click for larger. Credit: findtarget.com

It is said that on a January night in the year 1610 Galileo turned his telescope towards Jupiter and he saw “three fixed stars, totally invisible by their smallness”.  Thoroughly intrigued subsequent observations on different nights showed the “fixed stars” indeed moved, sometimes even disappearing.  He discovered a fourth moon a week after the initial observation.

How could this be?  Well of course he came to the conclusion they were orbiting Jupiter.  He published his observations in pretty short order, in March 1610 in a paper titled Sidereus Nuncius or Starry Messenger.  The observations were confirmed in 1611 at the observatory of Christopher Clavius.

Galileo may have received a hero’s welcome in Rome and had fame in much of Europe the thought of him turning the comfort of Aristotelian Cosmology on it’s ear did nothing for his standing with the church and it wasn’t too many years later his troubles began.

Instead of plowing ahead with his troubles let’s get back to his telescope.  The telescope was invented in 1608 by Dutch spectacle makers, supposedly the inventor was Hans Lipperhey but nobody can prove it.  In early 1609 you could buy one in Paris and by August of that year they made their way to Italy.  Galileo couldn’t get his hands on one but being the resourceful fellow and after he overcame some technical problems, he put his knowledge about lens making to work and he just made his own.

So what does this have to do with anything?  What Galileo could see with that 20 power telescope you can see with a pair of binoculars and I would like to suggest you take a look at Jupiter over the coming nights and look at Io, Europa, Ganymede and Callisto and note how they move.  Jupiter is super easy to find, just look south (almost due south at 8 pm your local time) it’s the brightest thing out there.  Oh sure if you make a sketch you can even figure out which moon is which quite easily on a number of sites, one of my favorites is at  Western Washington University – simple and clean.

Also while you are at it, okay, a little later in the night or early morning look for comet Hartley 2, it’s a great time because there is no moon.   Basically wait until you can see Orion, then look along a line from Orion’s belt and draw a line from Gemini, the comet will be in that area.  Here’s a little chart to help you.