Astral Observatory

From Zelda Wiki.org

The Astral Observatory is a small building out side of the walls of Clock Town in Majora's Mask. The only way to get here is through a hidden passage in East Clock Town. It is home to a giant telescope, which is able to view the entire landscape of Termina. The passage to the observatory is guarded by one of the 6 children of the Bombers Gang. If you want to get past him, you must tell him the secret password he asks for (the password varies). The password is acquired by blowing up the balloon in North Clock Town, talking to Jim, finding every member of the Bombers hidden throughout town, and repeating this process as Hylian Link.

Once the player enters the observatory, he or she must go through a small sewer, defeat a Skulltula, destroy another balloon, then go up the ladder leading to the observatory itself. At the entrance the player will meet the famous dancing scarecrow. If you go upstairs, the player will find the astronomer named Professor Shikashi with the huge telescope overlooking Termina Field. The Moon's Tear can be found here, which is required to start the Deku Flower Trading Quest.

Regarding the Moon's Tear, when you check the Moon's Tear inside the glass case next to the telescopem Professor Shikashi will comment on how he finds the stones falling from the Moon's eyes, and how they have been falling recently. This might be a hint that the Moon is upset for some reason, and is crying because of it. This might be because it has been pulled from it's orbit, the fact it will crash into Clock Town, the curse Majora has put on it, or perhaps another reason entirely.