The two days of the year when neither hemisphere is tilted towards the sun are the spring equinox and the autumnal equinox.

* Spring Equinox: Around March 20th or 21st in the Northern Hemisphere (around September 22nd or 23rd in the Southern Hemisphere)

* Autumnal Equinox: Around September 22nd or 23rd in the Northern Hemisphere (around March 20th or 21st in the Southern Hemisphere)

On these days, the sun's rays shine directly on the equator, and both hemispheres receive equal amounts of sunlight. This means day and night are approximately equal in length everywhere on Earth.