The March equinox – aka the vernal equinox – marks the sun’s crossing above Earth’s equator, moving from south to north. Earth’s tilt on its axis is what causes this northward shift of the sun’s path across our sky at this time of year. Earth’s tilt is now bringing spring and summer to the Northern Hemisphere. At the same time, the March equinox marks the beginning of autumn – and a shift toward winter – in the Southern Hemisphere.