Question

What event, which occurs twice a year when the sun crosses Earth's equator, recently
marked the start of autumn in the Northern Hemisphere?

Answer 1

Answer:

the autumnal equinox (when day and night are of equal length)

Explanation:

The first event occurs around the 22nd or 23rd in the month of September. What usually happens is that regions around the Northern Hemisphere (which includes all of North America and Europe) experience an equal length of day and night.

While the second event occurs around March 20th or 21st mainly observable in countries found in the Southern Hemisphere.