Many people anxiously await the first day of summer and look forward to activities that are tailor-made for warm weather. The first day of summer is known as the summer solstice, which marks the official start of astronomical summer. The solstice features more hours of daylight than any day of the year, according to Space.com. The next summer solstice in the Northern Hemisphere occurs on June 20, 2024 (the Southern Hemisphere celebrates the solstice on December 21, 2024).