Happy Summer Solstice, Dahlgren!
June 21, 2017
Today is the Summer Solstice, which marks the first day of summer in the Northern Hemisphere. It's also the longest day of the year for anyone north of the Equator. Here are some fascinating facts about this annual phenomenon.
- Because the Earth orbits the sun on a tilted axis, the Northern Hemisphere gets more sun exposure between March and September. The peak sunlight is between June 21 and June 22, hence the Summer Solstice.
- On Tuesday, June 21, most people in America will get 1.5 extra hours of sunlight. This time gets longer the further north you are (for example, Iceland gets about 20 hours of daylight during the Summer Solstice!)
- Just because the Summer Solstice gives us more sunlight doesn't mean that it's the latest sunset or the earliest sunrise of the year.
- Every year, the Earth's rotation slows slightly due to tidal friction. This means that every year, the days get very, very slightly longer. 4.5 billion years ago it took just 6 hours for the Earth to complete a rotation, while today, of course, it takes 24 hours.
- Despite the slowing of Earth's rotation, it doesn't mean that each year marks the new longest day in history. This is because there are other factors affecting the rotation besides just tidal friction (including melting glacial ice, geologic activity at the planet's core, earthquakes and more).