The Science Behind the Summer Solstice

Today – Thursday, June 21 – is the summer solstice in the northern hemisphere. But what causes this change in seasons? And what exactly is a solstice? It’s all about Earth’s tilt!

Many people believe that Earth is closer to the Sun in the summer and that is why it is hotter. And, likewise, they think Earth is farthest from the Sun in the winter.

Although this idea makes sense, it is incorrect. There is a different reason for Earth’s seasons.

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Earth’s axis is an imaginary pole going right through the center of Earth from “top” to “bottom.” Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth’s surface gets some of each.

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Earth has seasons because its axis doesn’t stand up straight. Today, the north pole is tipped toward the Sun, and the south pole is tipped away from the Sun. The northern summer solstice is an instant in time when the north pole of the Earth points more directly toward the Sun than at any other time of the year. It marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

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To mark the beginning of summer, here are four ways to enjoy the many wonders of space throughout the season: 

1. Spot the International Space Station

As the third brightest object in the sky, the International Space Station is easy to see if you know when to look up. Sign up to get alerts when the station is overhead: https://spotthestation.nasa.gov/.
Visible to the naked eye, it looks like a fast-moving plane only much higher and traveling thousands of miles an hour faster!

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2.  Treat your ears to space-related podcasts

From our “Gravity Assist” podcast that takes you on a journey through the solar system (including the Sun!) to our “NASA in Silicon Valley” podcast that provides an in-depth look at people who push the boundaries of innovation, we have podcast offerings that will suit everyone’s taste. For a full list of our podcasts, visit https://www.nasa.gov/podcasts.

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3. Explore space by downloading NASA apps

Our apps for smartphones, tablets and digital media players showcase a huge collection of space-related content, including images, videos on-demand, NASA Television, mission information, feature stories, satellite tracking and much more. For a full list of our apps available for download, visit https://www.nasa.gov/connect/apps.html

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4. Watch launches to space

This summer, we have multiple opportunities for you to take in the sights of spacecraft launches that will deliver supplies and equipment to astronauts living aboard the International Space Station, explore our solar system and much more. Be sure to mark your calendar for upcoming launches and landings!

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com