Happy solstice! It's the shortest day of the year in the Northern Hemisphere, and the longest day of the year in the Southern Hemisphere.

Earth tilts on its north-south axis with respect to the plane of its orbit by 23.4 degrees. Over the course of one year, each hemisphere gets a turn in more direct sunlight, which causes our seasons.

When either the North or South Pole is pointed most directly toward the Sun, it's called a solstice. Today at 11:28 a.m. EST (16:28 UTC), it's the South Pole's turn. From a northerner's perspective, the Sun is as far south as it will be for an entire year. That's why our days have been getting shorter—the Sun doesn't stay above the horizon as long.

If you're the type of person that needs pictures to visualize this, fear not: We have an army of Earth-observing satellites at our disposal to help.

Himawari-8 is a Japanese weather satellite. It's in geostationary orbit, where satellites match the rotational speed of Earth, allowing them to hover over the same spot. Here are two pictures of Earth by Himawari-8. The image on the left was taken on northern solstice (June 20), and the image on the right was taken December 19, two days before southern solstice. Can you visualize the Sun's position in each image?