Eppure Egli Ruota

Shortly after remaining alive -- or immediately before that -- Galileo Galilei allegedly muttered "Eppur si muove", in a legendary reference to a certain rocky planet that moves around a solar-type star in the habitable zone of our own solar system!.. Legend says he would say such a thing in presence of some irrefutable evidence that the given earthy planet would, in fact, show the aforementioned movement...
Well, I now say "Eppure Egli Ruota" inspired by this...
I took a picture of Jupiter; not a normal picture, though!.. In between the telescope and the sensor there was a weird light-wasting gadget capable of spreading wavelengths of light along one direction of the focal plane.. Science guys refer to it as a "Spectroscope"!..
The thing is it has enough resolution in picking out different wavelengths to actually reveal the Doppler effect on "stuff" moving at sufficiently fast speeds and in adequate directions. Here is what you get when pointing the slit spectrograph to Jupiter:

The horizontal "line" has a thickness identical to the diameter of the planet. The vertical dark lines are particular colors that our atmosphere absorbs. The oblique darks lines are absorption lines from the solar light itself, being reflected by the moving (turning) "surface" of Jupiter!
The inclination of the lines is intrinsically related to the speed at which the planet is turning. Calculating it only roughly, gives me a value between 8 km/s and 10 km/s that is a bit below Wikipedia's mentioned speed of 12.6 km/s. I did not have a special care in aligning the slit with Jupiter' equator, so this is well expected!
So, this Ziggy-zaggy picture is, actually, one other way of "seeing" Jupiter from Earth.. Here, Jupiter is not round-looking, it seems quite still.. Yet, "he" turns!