In Act 3, sc. 1, the players are practicing, in the woods, for their play which they hope to perform at the wedding of Theseus and Hippolyta. In the play, Pyramus and Thisbe are supposed to meet in the moonlight according to Quince. He then wonders how they will bring moonlight into a chamber (room) since they won't be outdoors. Snout asks if there will be moonlight on the night of their performance. Bottom suggests that they look into an almanac to see the weather forecast and the presence of a moon that night. Quince checks the almanac and says that yes, indeeed, there will be moonlight the evening of the wedding, so Bottom suggest opening a casement window and let the moonlight in that way (ll. 46-57). The players are buffoons and their worries and suggestions are ridiculous. This part of the scene where the players also discuss the need for two prologues so as not to frighten the ladies with the player playing the lion and the need for someone to play a wall. These ludicrous concerns highlight the silliness of the scene and the players and create comedy.
For scholars who attempt to make sense of the copius moonlight references in this play, the almanac exchange is one of the more confusing moments in the play. The mechanicals worry about incorporating a moon into their performance since, according to their sources, Pyramus and Thisbe meet by moonlight. Bottom is instructed to consult an almanac to 'find out moonshine'. He does so and is overjoyed to learn that the moon will shine on the night of Duke Theseus' wedding.
In fact, this is balderdash. The opening lines tell us that the wedding takes place on the night of the first visible new moon. Such a crescent would be low on the horizon and visible for a very short time right about sunset. The OED lists the first instance of 'moonshine' as meaning 'nonsense' some years after the composition of MND. But the exchange here makes perfect comedic sense if Shakespeare is playing on that meaning of the word. Bottom is instructed to go to an almanac to discover moonshine (nonsense) and he does just that.
Luckily, the mechanicals decide to circumvent the problem of physical moonlight by having one of their number impersonate the moon.