Moon City Observatory is one of the locations in Putt-Putt Goes to the Moon.
The observatory can found to the left of the location where Rover and Putt-Putt work together to retrieve the steering wheel. However, it is not necessary to go here in any version of the game.
In the observatory is a telescope, which Putt-Putt can use to find constellations. The constellation that Putt-Putt sees in the telescope when the latter is clicked will automatically connect the stars together and Putt-Putt will say which constellation it is and describe it.
There is also a solar system diagram behind Putt-Putt in the observatory. Clicking on the planets, the sun, or the moon will cause the speaker on the ceiling to give a description of whatever was clicked on.