Midsummer

During my ongoing literature review I often discover interesting facts about things I’ve never thought about. Sometimes I can connect these facts with my own observations: The result is mostly a completely new idea why things are as they are. Maybe these ideas are new to you, too. Therefore I’ll share my new science based knowledge with you!

This week: This time, it’s midsummer! But what is so special about this day?

Due to a fortunate coincident, this week’s „Finding of the Week“ is published on the longest day in the northern hemisphere of our Pale Blue Dot[1]. In this case, I like to step a little bit away from the usual computer game topics and celebrate this special day in a more analytical way.

June 21st is also known as „midsummer“ or „St. John’s Day“ and this day is especially celebrated in Northern Europe or to be more specific in Scandinavia and the Baltics[2]. But also other nations are celebrating this day with some special events like bonfires. However, June 21st is not only a special day to celebrate for most cultures, it is also the longest day for the northern hemisphere of our Earth, because it is the day of the summer solstice. On summer solstice the northern half of our Earth has the longest exposure to the sunlight during the whole year.

The reason behind this yearly event lies in the combination of two rotation axes. On the one hand, our Earth is completing an orbit around the Sun every 365,25 days. The 0,25 day is the reason why every 4th year is leap year: we need to synchronize our calendars with the orbital period of our home planet.
On the other hand, the Earth is also rotating around a rotation axis going through its poles. This rotation has a period of 24 hours relative to the Sun and is resulting in a „day“ on our Earth.

Unfortunately, these two rotation axes are not completely explaining the occurrence of the summer solstice. The missing information lies in the tilt of the rotation axis of the Earth relative to the orbital plane around the Sun. The rotation axis is not perpendicular to the orbital plane and is instead tilted by about 23,5°. This axial tilt is the reason behind the summer solstice. It is also the reason for the seasons, the winter solstice, the midnight sun and the polar night. During one orbit around the Sun, the axial tilt is changing the sunlight exposure of certain parts of the planet. At the very special day of the summer solstice, the northern part of the planet is directly pointing towards the Sun. At the same time, the southern part of the planet is directly pointing away from the sun. During the days around the solstices, some parts of the planet experience sunlight exposure throughout the whole day (midnight sun) and other parts of the planets are not seeing the Sun for several days (polar night).[3]

The amount of sunlight per day is also affecting our climate and is creating the seasons. During summer time, the Sun has more time to shine on the „summer“ side of the globe thus heating it up. During winter time, the Sun has not enough time to heat up the environment of this part of the globe and the temperatures are decreasing again.

Interestingly, the great heat is mostly experienced after the summer solstice-when this part of the Earth is slowly drifting away from pointing directly to the Sun-and not around this event. The reason behind this comes from the fact, that it takes some time to heat up the environment. This is also why the coldest months of the year are mostly after the winter solstice: the environment needs some time to cool down.

With this special knowledge in mind, it is now even more impressive to watch the very late Sun set at this special day. It has become more than just a beautiful view, it is the result of something big.

Setting sun

Happy midsummer!