Earliest summer solstice in 228 years happens Thursday

The summer solstice happens Thursday at 4:51 p.m. ET. It's happening a day earlier than usual because the Gregorian calendar needs a course correction.

Astronomical summer starts a little earlier this year, with the summer solstice Thursday. It's the earliest start of the season in the past 228 years. 

With the scorching temperatures across the U.S., it's already felt like summer for weeks. If you ask a meteorologist, it's been summer since June 1. However, the start of astronomical summer begins with the summer solstice.

This year, the summer solstice happens June 20 at 4:51 p.m. ET, when the Sun is directly above the Tropic of Cancer. It's also known as the longest day of the year because it has the most daylight. 

While the summer solstice can fall between June 20 and 22, it last occurred on June 20, 1796, when George Washington was president. 

Why is the summer solstice early this year?

These dates can vary yearly since it takes the Earth 365 days and 6 hours to make one complete orbit of the Sun. That is why the Gregorian calendar adds a leap year every four years with 366 days. During leap years, solstices and equinoxes happen earlier than the previous year, moving up the summer solstice by about 45 minutes every four years. 

The summer solstice will happen about 40-50 minutes earlier until the next century.

Solstices would happen indefinitely earlier every four years except for another quirky rule of the Gregorian calendar to keep it in sync with Earth's orbit of the Sun.

Any year divided by four is a leap year except years evenly divided by 100 (century years), which are only leap years when divisible by 400. This means 2100 will not be a leap year, according to Timeanddate.com. Skipping these leap years helps keep the calendar on time with Earth's dance around the Sun. 

Many cultures celebrate the summer solstice with festivals and bonfires. For some who practice yoga, it can involve the tradition of performing 108 sun salutations on summer and winter solstices to welcome the new season. 

As a bonus, this year's summer solstice happens before a full Moon. June's Strawberry full Moon rises at 9:08 p.m. ET. It will also be the lowest full Moon of the year, making it appear extra full.