The 2026 Mid-Autumn Festival in Chicago is so early due to the astronomical alignment of the moon's phases and the Gregorian calendar.

The Mid-Autumn Festival, also known as the Moon Festival, is traditionally celebrated on the 15th day of the 8th lunar month. This year, the festival falls on September 9, which is earlier than the typical date. The reason for this early date is rooted in the lunar calendar, which is based on the phases of the moon. The lunar year is approximately 11 days shorter than the solar year, which is why the dates of the lunar holidays can vary each year. In 2026, the 15th day of the 8th lunar month falls on September 9, which is earlier than the usual date.

The Gregorian calendar, which is the calendar system used by most of the world today, is a solar calendar that is adjusted for leap years to keep it aligned with the astronomical year. The leap year adjustment helps to synchronize the calendar with the solar year, but it does not affect the lunar calendar. Therefore, the early date of the Mid-Autumn Festival in 2026 is solely due to the lunar calendar's alignment with the moon's phases.

According to the Chinese Lunar Calendar, the Mid-Autumn Festival is celebrated when the moon is at its fullest and brightest. This year, the full moon is expected to occur on September 9, which is earlier than the typical date of the festival. The early date is not uncommon, as the festival can occur as early as August 15 or as late as September 15, depending on the lunar calendar's alignment with the Gregorian calendar.

In conclusion, the 2026 Mid-Autumn Festival in Chicago is early due to the alignment of the moon's phases with the 15th day of the 8th lunar month, which falls on September 9. This early date is a result of the lunar calendar's relationship with the moon's phases, not influenced by the Gregorian calendar's leap year adjustments.