The June solstice of 2018 happened this morning at 6:07 a.m. ET.
To people who live in Earth’s northern hemisphere, Thursday marks the longest day of the year. It also signals the end of spring, the arrival of summer, and a gradual retreat toward the fall season, which is marked by an equinox.
For those in the southern hemisphere, it’s exactly the opposite: The June solstice marks the start of winter, when days have reached their shortest and darkest, though daylight will last longer and grow stronger as the September equinox approaches.
Two things drive this all-important seasonal clock: Earth’s tilted axis and the planet’s orbit around the sun.