Instructions
Play the game until the Second Week of Spring arrives. At this time, you are introduced to Cinnamon, a girl who is obsessed with constellations.
Leave your house and walk towards the bridge that leads towards the Church District. Speak to Cinnamon to learn about constellations. Now that she has told you about them, you're able to find them by looking at the sky.
Climb up the Mountain Path, located left of Cornucopia Trees, to get to the observatory on any night when the weather is clear.
Press the "1" button to look up at the sky. Depending on the in-game time and what season it currently is, you may find a constellation. Once a constellation is found, its outline is traced in the sky.
Talk to the eligible girls in town after viewing a constellation to see if finding it has had an effect on any of them. If you speak to the correct person, you get a special event and, occasionally, a reward.