when is the first day of spring

The first day of spring varies depending on the hemisphere:

1. Northern Hemisphere: In the Northern Hemisphere, the first day of spring is around March 20th or 21st.

2. Southern Hemisphere: In the Southern Hemisphere, the first day of spring is around September 22nd or 23rd.

These dates are determined by the vernal equinox for the Northern Hemisphere and the autumnal equinox for the Southern Hemisphere. The equinox is the point in Earth's orbit around the sun when day and night are of approximately equal length.

During the vernal equinox in the Northern Hemisphere, the tilt of the Earth's axis is such that the Sun appears directly above the equator, marking the start of spring. In the Southern Hemisphere, during the autumnal equinox, the tilt of the Earth's axis is such that the Sun appears directly above the equator, marking the start of spring in the Southern Hemisphere.