Some natural phenomena need few words to explain why they're fascinating. Eclipses, transits, and phases in astronomy tend to fall into that category. Here's a stunning sequence of images captured by the Hubble Space Telescope's Wide Field Camera 3 showing the triple conjunction and transit of the large Jovian moons Europa, Callisto, and Io over some 42 minutes in January 2015.
Jupiter of course has a lot of moons, 67 confirmed ones in fact. Some of these smaller ones were in on the act too, they're just too small to notice easily. Here's a guide to the position of 2 others - Thebe and Amalthea.
So in fact this was a quintuple conjunction event!
And finally, in animated form.