Orange Beach, Ala. — (OBA) — The first official day of summer isn’t always June 21. In fact, the start of summer can shift slightly each year. This change happens because Earth’s orbit and tilt don’t perfectly match the calendar. In 2025, summer begins on Friday, June 20 at 9:42pm CDT.

Here on the Alabama Gulf Coast, that evening marks the exact moment of the summer solstice. It’s when the Northern Hemisphere tilts most directly toward the Sun. Today we’ll see the longest daylight of the year, at approximately 14.5 hours.

Even though June 21 is more familiar as the start of summer, this year’s solstice is one day earlier on June 20.

The reason for the shift is how Earth’s seasonal cycle interacts with our calendar. A tropical year—the full seasonal cycle—is about 365.2422 days long. But our calendar only has 365 days.

That small difference adds up, so we add an extra day every four years. These leap years keep the seasons mostly on track with the calendar. But even leap years need fine-tuning.

Years divisible by 100 are not leap years, unless they’re also divisible by 400. These extra rules help us stay synced with Earth’s orbit. Still, tiny shifts keep happening.

Over thousands of years, the solstice slowly moves on the calendar. The next time summer begins on June 22 will be in the year 2203. Until then, enjoy the early start.