Which event marks the longest daylight period of the year?

• A. Summer Solstice
• B. Winter Solstice
• C. Equinox
• D. Solstice Day

Answer: (A)

Longest daylight happens when the Sun follows its highest path in the sky, which occurs at the summer solstice. At this moment the Sun is at its most northerly position due to Earth's tilt, so the horizon is extended with daylight for the maximum number of hours. In the northern hemisphere this happens around June 20–22, and after this point the days begin to shorten toward the winter solstice, the shortest day. Equinoxes are when day and night are nearly equal in length, not the longest. The term “Solstice Day” isn’t a standard astronomical label.