Longest Day of the Year - Happy Solstice!

Tuesday, June 20, the Northern Hemisphere will have the most amount of sunlight in a day all year - the Summer Solstice! In astronomical terms, summer begins today at 11:24 PM. Our summer constellations will take the prominent positions in the South after sunset.

Our star, captured by the Solar Dynamics Observatory in April 2016.

So why is June 20th the longest day of the year?

We have solstices and equinoxes (and seasons) because of the Earth's tilt and orbit around the Sun. While the Earth orbits the Sun, one hemisphere is tilted toward the Sun while the other is tilted away. The hemisphere that is tilted toward the Sun gets more direct sunlight than the opposite hemisphere, and so is in summer. In the Southern Hemisphere, June 20 is the shortest day of the year, because it is tilted away from the Sun - they are in winter. 

This image shows the Sun's path through the sky on the Summer Solstice (upper), Equinoxes (middle), and Winter Solstice. Our days are long in the summer because the Sun takes longer to get from sunup to sundown. Image Credit

The June Solstice is the day that we are most tilted toward the Sun in the Northern Hemisphere, so the Sun takes the longest time to go from sunup to sundown. It rises the farthest north of east, and sets the farthest north of west that it will all year.  In Peoria, we have 15 hours of sunlight on the Solstice.

Even though today is the longest day of the year, we can expect the months ahead to be hotter than June. July and August are usually our hottest months for the same reason that 3 or 4 PM is often the hottest time of the day (not noon when the Sun is highest). The Earth takes a while to warm up after the cold winter. As the season progress and we have more long days and short nights, the heat builds. This phenomenon is called the "lag of the seasons".

I hope you can get out and enjoy the sunlight today, and the stars tonight. You can always learn what's happening in the sky and get the latest news from space at the Dome Planetarium at the Peoria Riverfront Museum. Follow us on Facebook and Twitter for daily updates!  

Learn about asteroids and meteorites on Asteroid Day! Activities are free with admission.