Fun with The Galilean moons

[John]

As Jupiter's 4 Galilean moons are spread out nicely and the seeing was half decent I thought I'd try a little game that I've been meaning to try for a while.

The key to this is not looking up the position of the moons before observing of course !

Using 200x magnification for a nice crisp image with my 12" dob, I examined the 4 moons carefully and tried to put them in order of their apparent size as seen through the eyepiece. The moons that appeared to be largest and smallest were reasonably easy to determine but for a while the remaining two seemed more or less equal. After I while longer I felt that one just slightly edged the other possibly so I assigned them a ranking and then retired inside for a coffee and quick look at the Sky & Telescope applet to see which moon was which, position wise. 

As my knowledge of the Galilean moons is not encyclopedic I had to look up their actual diameters in Nortons Star Atlas to see how close I'd got to the right size order.

Well what do you know - I got it right !!!

I'm sure other observers have done this before many times and there is nothing really scientific about it but stuff like this does add some fun to observing and makes you look just that bit harder 

[YKSE]

Nice game, John. Should be worth trying in the coming days too, when the viewing objects are quite limited except double work.

[cotterless45]

Neat, it's lovely to see the different alignment of moons. I remember the 4 all at different heights at one side. They looked like a swarm of bees !

Over the course of a long session I keep going back to Jupiter as it changes so very quickly.

Nick.

[mjpfc]

For heavens sake watch yourselves!

Its like doing the lottery with the same numbers each week, you cannot stop in case they come up.

I panic if I inadvertaintly turn the page of a mag with the Jovian moons ephemeris on in case I catch a glimpse of

tonight's positions ........My life is in ruins and my therapist is on his 3rd foreign holiday in 3 months.

and as for Messier, as soon as time travel is invented I vote we go back and strangle the man at birth.

Apart from that I'm fine, as long as I can stop counting the stars inside the square of Pegasus before I even start.......   

[YKSE]

Tried it with EPs for 200x to 400x, still got IO and Calisto wrong

A positive side effect though: I think I remember the names, relative sizes and postions now.