Earth actually takes 365.2422 days to complete one trip around the sun, and as a result our calendar falls behind by about a quarter day each year. So we tag on a full day every fourth year, making it 366 days. This helps keep our calendar in sync with Earth’s movements and seasons.

But that creates another issue. Leap years are about 11 minutes longer than Earth’s real orbital period. To fix this, we skip the extra day in years that are divisible by 100 but not divisible by 400. So there were no leap years in 1700, 1800, and 1900, and we won’t have one in 2100, 2200, or 2300.

The ethereal effect is caused by sunlight reflecting off dust particles