*MISSABLE* You need to complete the solar system puzzle in 15 moves or less. The idea is to line up all 8 of the planets in their location on the left side of the sun. The set-up for the puzzle is like this:
Planets are numbered from their final locations on the left, 1 through 8, with 1 being the farthest to the left, and 8 being the farthest to right (closest to sun).
Switch 1 (top): Moves planets 1,4,8.
Switch 2: Moves planets 3,7.
Switch 3: Moves planets 1,6.
Switch 4 (bottom): Moves planets 2,5,7.
Hit the switches in this order for a total of 15 moves: Switch 1 x 7 times, Switch 2 x 1 time, Switch 3 x 2 times, and Switch 4 x 5 times.
*GLITCH WARNING* For some reason, this achievement just does not unlock when completing the requirements some times. If it doesn't unlock for you on the first attempt, try completing closing the entire game, relaunching it, and changing the difficulty and running back through the episode to this point to give it another go. Even this may not work. Two other possible solutions (or orders) you can try that will line the planets up in 15 moves are:
Alternative 1: Switch 2 x 1 time, Switch 3 x 2 times, Switch 1 x 7 times, Switch 4 x 5 times.
Alternative 2: Switch 1 x 3 times, Switch 3 x 6 times, Switch 4 x 5 times, Switch 2 x 1 time.