The spring comes when the sun's warming rays line up perpendicular to earth's axial tilt. At the time of equinox at earth's equator, the sun appears almost directly.
Explanation:
When the earth travels around the sun its orbit, the north to south position of the sun changes over some year due to the changing orientation of the earth's tilted rotation axes. The dates of zero tilt of the earth's equator correspond to the spring equinox and autumn equinox.
The tilt of the earth is that earth will lean towards the sun (summer) or lean away from the sun (winter) for 6 months. At this time spring and autumn will occur. The earth's movement around the sun causes the seasons.
Hence, the earth is tilted during the spring and fall equinoxes because the spring comes when the sun's warming rays are perpendicular to earth's axial tilt.
