Caption: Jupiter and Galilean moons as they appear on the sky.

Features:

1. The Jovian band structure is clearly visible, but NOT the Great Red Spot.

2. From left to right, the Galilean moons are Ganymede (or Callisto), Io, Europa Callisto (or Ganymede).

3. Io must stay within about 3 Jupiter diameters of Jupiter, and so the Galilean moons identified as NOT Io are too far from Jupiter to be Io.

4. Europa must stay within about 4.5 Jupiter diameters of Jupiter, and so the Galilean moons identified as NOT Europa or Io are too far from Jupiter to be Europa.

5. The Galilean moons are nearly on a line. This is because they all orbit in same orbital plane to within 0.5° (see Wikipedia: Moons of Jupiter: List) which plane is almost the same as Jupiter's equatorial plane---with which the Jovian band structure is aligned and which has orbital inclination of 1.305° from the ecliptic plane.

6. As a result of the near alignments, one just observes the Galilean moons projected on the sky oscillating back and forth around Jupiter approximately on a line.

   For each Galilean moon, the amplitude of the oscillation is approximately the mean orbital radius.