Planetary calendar room

The Planetary calendar room was a large machine with in Wan Shi Tong's library, in the middle of the Si Wong Desert. By manipulating various levers, one was able to see what the sun, moon and stars would be like on a certain date.

History
When Team Avatar encountered Professor Zei at the Misty Palms Oasis' cantina, they ventured with him into the desert in search for Wan Shi Tong's library. Inside, Sokka discovered a small burned piece of parchment which read, "The Darkest Day in Fire Nation History" and had a date on top of it. After he discovered that the whole wing dedicated to the Fire Nation was burned down, thus preventing him from finding out when happened on "the darkest day in Fire Nation history", a knowledge seeker arrived and led Sokka and the others to the planetary room. The fox creature entered through as small opening to the right of the large golden room and opened it from the inside. When the foursome entered, the fox showed them how the planetary room worked by pushing a lever. Zei exclaimed that the room was a "true marvel, a mechanical wonder". Katara suggested that Sokka entered the date that he found on the parchment on the dials in the middle of the room. When he did so, the planetary heavens moved and showed that the darkest day in Fire Nation history was actually a solar eclipse, thus leading Sokka to discover that Firebenders lose their Firebending during a solar eclipse.

At the moment Sokka suggested a first draft of the invasion plan, Wan Shi Tong appeared, claiming that the visitors of his library had betrayed his trust by using the knowledge of the library to hurt other people. As a result of this, the Knowledge Spirit started to sink his library in order to trap everyone inside. While Katara and the professor headed for the exit, Sokka and Aang returned to the planetarium in order to find the date of the next solar eclipse. After finding out that it was only a few months away, they too left the room and the library.

The planetary calendar room was eventually lost to the sands with the rest of the library when Wan Shi Tong sunk it beneath the desert.

Design
This impressive machine was built by Wan Shi Tong and his seekers using phosphorescent crystals, jade, brass, and other fine materials. Though it may seem like advanced technology, the planetary calendar works on gears and cogs like a watch. The ceiling is domed, like that of a planetarium, with "stars" projected from a crystal. The room uses its crystal-made stars, along with several rotating planets, to act as a kind of almanac showing both recorded history and projected future planetary alignments.

In principle, the machine resembles the real-world Antikythera Mechanism, an ancient Greek clockwork device used for calculating positions of celestial bodies. Though significantly smaller in size, the core mechanisms involved are similar; with a series of intracate gears involved and actuated via a crank after the desired date is inserted by adjusting ring-shaped dials of varying scales.