When Does Summer Start 2024 California. Summer begins with the solstice on thursday, june 20, 2024, marking the astronomical first day of summer in the northern hemisphere. Summer starts at the moment when the sun is farthest north:

Here’s when the holiday falls in 2024 and why its celebrated. Astronomical summer ends at the fall equinox, when the sun is directly over the equator, and night and day are of roughly equal length.