Astral Observatory

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, who must be told a 5-digit password in order for Link to gain entry. The password is acquired by popping the balloon in North Clock Town, talking to Jim, finding every member of the Bombers hidden throughout town, telling the password to the Bomber guarding the passageway. Once Link regains his Hylian form and returns to the first day, he can play the game again to reenter the underground tunnels.

Once Link enters the tunnels, he 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 he meets the famous dancing scarecrow. Upstairs, Link 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, upon checking the Moon's Tear inside the glass case next to the telescope, 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.