AUSTIN (KXAN) — Today is the day. The summer solstice has arrived for the northern hemisphere, while the southern hemisphere gets to experience the winter solstice. For us northerners, Tuesday marks the shortest night of the year and the longest day. It also marks the first official day of summer.

Astronomy of the solstice

Why does today happen the way it does? The Earth orbits the sun, but it doesn’t do so perfectly. At some point in the distant past, something struck the Earth and knocked it off its axis. Due to this, the Earth’s orbit is tilted 23.5 degrees.

Because of this tilt, one side of the planet is always getting more sun than the other half (either the Northern or Southern hemisphere). On the solstice, the Earth reaches a point in its orbit where one of these halves is directly facing the sun and the other half is pointed completely away.

Because of the sun’s tilt, on the summer solstice the sun will reach its highest point in the sky at noon. According to the National Weather Service, this is most obvious in the Tropic of Capricorn. This tropic is 23.5-degrees south of the equator and runs through Australia, Chile and northern South Africa.

History of the solstice

The word solstice comes from two Latin words. Sol, which means sun, and sistere, which means to stand still. Historians believe humans have been observing the solstice since the stone age.

According to History.com, different cultures have celebrated different things around this time:

• Ancient Egyptians marked the solstice with the rising of the Nile River.
• Northern Europe celebrated Midsummer, a pagan holiday celebrated with bonfires, feasts and dancing.
• Christians celebrate the solstice as the birth of St. John the Baptist.

For many ancient cultures, the solstice served as the start of the new year. The ancient Greeks would celebrate this new year with a countdown to the Olympics. They would also celebrate the god of agriculture, Cronus. The ancient Romans would use this time to celebrate the goddess of the hearth, Vesta.

Is today the hottest day of the year?

Short answer, no. According to the National Weather Service, the hottest day of the year lags behind the summer solstice. This usually occurs three weeks later in the United States. This lag is because it takes longer for the ground and water to heat up than it does the air.

Average high temperatures continue to climb well past the solstice. In Austin, August is typically our hottest month.