The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Earth is tilted 23.5 degrees on its axis of rotation, and how the North Pole is oriented toward or away from the sun determines two of these astronomical dates.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

For most of the year, the Earth’s axis is tilted either toward or away from the sun. That means the sun’s warmth and light fall unequally on the northern and southern halves of the planet.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Northern Hemisphere’s spring — or vernal — equinox can land between March 19 and 21, depending on the year. Its fall – or autumnal — equinox can land between Sept. 21 and 24.

The Earth is tilted 23.5 degrees on its axis of rotation, and how the North Pole is oriented toward or away from the sun determines two of these astronomical dates.