People in the World of Avatar have limited knowledge about astronomy and the universe around them. This extends to knowledge of eclipses and solstices, which are featured extensively in history and events. This knowledge is vital, as astronomical occurrences can directly affect bending power.
A comet is a small celestial body that orbits the Sun. When close enough to the Sun at the edge of Earth's atmosphere, comets exhibit a visible coma or a tail. The coming of a comet can be also predicted as it is periodic.
- Main article: Sozin's Comet
Sozin's Comet passes close to the Earth every one hundred years. Firebenders are able to draw power from it as they normally do the Sun, greatly enhancing their abilities. Fire Lord Ozai claimed it enhanced firebending by to the equivalent of one hundred Suns. Sozin used the power of the comet to eliminate the airbenders in an unsuccessful attempt to kill the Avatar; he was the first person to draw power from the comet to commit genocide and thus, it was renamed in his honor.
An eclipse is an astronomical event that occurs when one celestial object moves into the shadow of another. People know the cause of these phenomena and can predict them through a planetary calendar room.
Waterbending draws its power from the moon. Though the Moon Spirit's mortal form is known to influence the bending art, the effects of astronomical events are not clearly defined. During a lunar eclipse, the moon is merely hidden from view in the shadow of the Earth, with no interfering body in between, unlike a solar eclipse, where the sun is actually obscured by the satellite.
- Main article: Day of Black Sun
A solar eclipse, such as the one that took place on the Day of Black Sun, refers to a day when the sun is entirely blocked out by the moon, rendering firebenders powerless. A solar eclipse affects firebending by blocking the sun's heat and light, both of which firebenders use to control their bending.
The invasion of the Fire Nation took place on the Day of Black Sun. The invaders forced their way up the main route to the Capital City, and with the eclipse fast approaching, the firebenders were in full retreat. The invaders put on their eclipse glasses for observing the eclipse safely, without unnecessarily damaging their eyes. Meanwhile, the Avatar and his friends encountered War Minister Qin in the caverns and, with him totally defenseless, he told them of the Fire Lord's whereabouts.
- Main article: Meteor
A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface.
- Main article: Outer space
Outer space is the term for the massive amount of empty space on the plane of existence surrounding the entire world. It comprises the entire universe. Avatars can travel to outer space when controlling the Avatar State.
A solstice is an astronomical event that occurs twice a year when the tilt of the Earth's axis is most oriented toward or away from the sun, causing the star to reach its northernmost or southernmost extreme in the sky during the day. Solstices, as other astronomical phenomena, can be predicted. During the solstice, the Spirit World and the natural world are at their closest, while during the equinox they are at their farthest.
- Main article: Summer solstice
The summer solstice is a natural phenomenon that occurs when the sun is at the closest angular distance to the equator. The winter solstice and the summer solstice are the only times when the Spirit World and the natural world come close together enough to interact freely with each other for extended periods of time. This event was experienced when Aang meditated in order to communicate with Avatar Roku about the latter's past events experienced when alive, such as his friendship, friendly rivalry and ensuing conflict with his friend and the eventual Fire Lord Sozin.
When Zuko and Aang journeyed to the ancient Sun Warrior civilization, they came across a chamber whose entrance was controlled by a celestial calendar. Zuko determined that the door would only open during a solstice.
- Main article: Winter solstice
The winter solstice is a natural phenomenon that occurs when the sun is at its greatest angular distance from the equator. It is also the shortest day of the year. As the solstice approaches, the natural world and the Spirit World grow closer together until the line between the two is blurred. During the solstices, spirits can exert incredible power in the natural world. This is also the ideal time for people with the ability to enter the Spirit World. Spirits can appear in the real world for a short time on the solstice, like Avatar Roku.
- Main article: Eclipse glasses
Eclipse glasses are a gadget invented by the mechanist. When the invasion force marched to the Fire Nation Capital on the Day of Black Sun, they could observe the eclipse safely as a means of keeping track of their time. They used these glasses to protect their eyes, as staring directly into an eclipse can damage the retina.
A lunar calendar is one that is based on cycles of the moon phase.
- Main article: Star chart
The star chart is a map of the stars and constellations. The equivalent of Earth's North Star, Polaris, is centered on the chart, allowing those who use it to find the true direction of north when in the Northern Hemisphere.
- Main article: Sunstone
- Main article: Zuko's telescope
Located in center of the courtyard at the Sun Warrior city, the celestial calendar is a large orange gem that refracts slivers of light onto a calendar on the ground. This gem is part of a celestial locking system that protects a sacred room. The room can only be opened on specific days, like the summer solstice. The Fire Sages also had such a calendar in the sanctuary of their temple on Crescent Island. As such, Aang was able to go to the temple on the winter solstice to speak to Avatar Roku.
- Main article: Crescent Island
Crescent Island is a volcanic island on the outskirts of the Fire Nation archipelago. The Fire Temple, the only structure on the island, was built there so that it aligned with the solstices and equinoxes as a calendar itself and housed the Fire Sages.
Planetary calendar room
- Main article: Planetary calendar room
The planetary calendar room is located in Wan Shi Tong's Library, in the Si Wong Desert. Aang and Sokka used the room to research information about the eclipse to plan the invasion of the Fire Nation.
- In the series, even in the midst of winter, the polar regions experience a normal day and night, while in the real world, the pole's extreme geographic location on the planet would yield either an extremely long period of daylight or an extremely long period of nighttime, depending on the season. If the Earth's axis operates similarly in the World of Avatar as it does in the real world, the North Pole should have been covered in three months of nightfall.