- This article is about the event. For the episodes, see "The Day of Black Sun, Part 1: The Invasion" and "The Day of Black Sun, Part 2: The Eclipse". For the battle, see Invasion of the Fire Nation.
The Day of Black Sun is a recurring celestial event during which the sun is entirely blocked out by the moon, rendering all firebenders powerless. The event is only known to have occurred twice during recorded history.
The first recorded Day of Black Sun was considered to be "the darkest day in Fire Nation history". The date upon which this phenomenon occurred was the nineteenth day of the seventh month, as indicated on a paper Sokka found in Wan Shi Tong's Library.
On the Day of Black Sun that occurred on the first day of the eight month in 100 AG, the Fire Nation Capital was invaded, with the objective of quickly defeating the Fire Lord and ending the Hundred Year War. However, the Fire Nation became aware of the imminent attack when Azula, Mai, and Ty Lee had infiltrated Ba Sing Se and were informed about the plans by Earth King Kuei, believing them to be allies of the Earth Kingdom. Due to this mistake, the Fire Nation was able to anticipate and prepare for the assault. The invasion force managed to reach the Fire Nation Royal Palace but were unable to escape after the eclipse ended, leading to the detainment of the adult participants while the younger members fled on Appa.
While the Day of Black Sun had been a loss for the forces storming the capital, other battles against the Fire Nation were successful, as King Bumi found the eclipse to be "the right moment to strike" and single-handedly liberated the city of Omashu, thus beginning the eventual liberation of occupied regions in the Earth Kingdom. This was also the day Iroh broke out of prison and escaped to the Earth Kingdom, paving the way for the eventual liberation of Ba Sing Se by the Order of the White Lotus.
Avatar: The Last Airbender
Book Three: Fire (火)
- In the real world, total eclipses have a similar duration time as portrayed in the series. However, the fact that people in the Fire Nation and Earth Kingdom could both see a total eclipse at the same time is fictional. The area on Earth where the moon completely eclipses the sun is roughly a few miles in diameter, a relatively small area compared to the area where the sun is only partially eclipsed, which can be as large as a continent. The eclipse's span can only be plausible if the planet in which the Avatar universe is located is considerably smaller than Earth, if the moon is closer to Earth or if the moon is larger in proportion to Earth, making its large coverage during an eclipse justifiable.
- Solar eclipses have no known effect on waterbending, even though the moon is out in front of the sun. However, during a solar eclipse, the moon is in the new moon phase, explaining why waterbenders would not experience the enhancing effects that the full moon provides.
- A solar eclipse is the only natural event known to leave firebenders powerless.
- The total eclipse lasts for only eight minutes.