Jupiter on July 13, 2019
Io’s Shadow on Jupiter
The good news was that one of the bright moons of Jupiter was going to cast its shadow
onto Jupiter’s disk (eclipse) and that such events are easy to observe in even small amateur
telescopes. The bad news was that the Jovian-Io eclipse would be in progress at sunset
and the bright gibbous-phased Moon was only a couple of degrees east of Jupiter. By the
time it was truly dark the eclipse would be over.
The sky was still bright at sunset, with only the large moon noticeable in the southern sky. I
knew approximately where Jupiter was, and it did not take me long to find it with binoculars.
I already had my travel scope, an 85mm refractor, setup on the deck waiting for the event.
Once found with the binoculars, I soon had Jupiter in the telescope. Even in the semi-blue
sky the four Galilean moons of Jupiter could be seen in the telescope. The evening air was
stable, so good detail could be made out on Jupiter, even in the small scope. I had to switch
to a higher power (124x) to locate the shadow of the moon Io on the planet’s disk (a black dot
in the drawing), but it was surprisingly easy. The sky had still not completely darkened by the
time the moon shadow had left Jupiter, but dark enough for me to enjoy the eclipse and make
a quick (40 minute) rough-draft drawing, placing the shadow-time at 21:00 EDT (Io’s shadow
moved reasonably fast) – and I still got to bed on time!!