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Sun 101
DCL
By Dillon Fernando

Happy Summer Solstice! Other than Facebook telling you that today is "officially" the first day of summer, why should you care about the summer solstice?

Here are the five things you need to know about the summer solstice:

(Note: The 2016 summer solstice overlaps with the appearance of June's full moon, known as the Strawberry Moon. The last time this happened was in 1967 and it will not happen again until 2062.)

  1. The summer solstice is the longest day of the year

The solstice is the one day of the year with the most amount daylight. Why? The sun rises slightly north of east and sets slightly north of the west. This means that the sun is in the sky for a longer period of time, therefore equaling more hours of daylight.

Some areas of mainland United States during the summer solstice could receive between 15-16 hours of daylight. The amount of daylight received during the solstice differs with respect to latitude. The more North you are; the more daylight you will receive.

The Northern hemisphere can expect to also see 1 to 1.5 more hours of twilight. If you live at the North Pole, you should see the sun throughout the night. If you live at the South pole, you will see no sun.

  1. The day marks the first day of summer

It's the first day of summer, yay!

For 2016, the June solstice occurs all over the planet at the same time. At 6:34 EDT, the Sun "hovers" directly overhead the Tropic of Cancer (the northern most circle of latitude), officially marking the summer solstice.

Depending on the year, the first day of summer either occurs on June 20, 21, or 22 in the Northern hemisphere. The variation is partially due to inconsistencies in our calendar only accounting for 365 days out of the 365.25 days it normally takes to orbit the Sun (same concept as leap year). However, the variation could also be attributed to time zone differences, the wobble in Earth's axis, and the gravitational influence of other celestial bodies.

Surprisingly, the summer heat is not caused by the Earth being closer to the sun. In the Northern hemisphere, the sun is the farthest away from the Earth during the summer and closest to the Earth during the winter. Summers are hot because the sun shines more directly on a hemisphere. However, as a result of these differences in solar distance, summers in the Northern Hemisphere receive 7% less sunlight than the Southern Hemisphere.

  1. Throughout history, several cultures and religions have embraced celebrating the solstice

On the solstice, the sun appears at its highest point in the sky. The name solstice comes from the Latin words sol (sun) and sistere (to stand still) because the sun visibly doesn't appear to change its position. This solar behavior inspired several celebrations from India to Finland to the United States.

Stonehenge is thought to be a prehistoric landmark that has served as a place of worship for thousands of years. Specifically, the mysterious stone structure was possibly used to celebrate the Summer Solstice, and several descend upon Stonehenge to this day to observe the sunrise. From some angles, the sun appears to balance itself atop the flat stone--a natural altar for the sun.

For the Galileo, the summer solstice was a slightly darker day. On the summer solstice of 1633, the Inquisition forced the scientist to recant his theory that the Earth revolves around the sun.

  1. A solstice occurs when the tilt of the Earth's axis is maximally pointed towards the Sun

While you might not physically feel it, the Earth actually rotates on a tilted axis.

Imagine a pole running through the north and south poles of the Earth--this is the axis the Earth spins on. Earth's axis titled 23.5 degrees relative to the plane of the Earth's orbit around the Sun. Scientists believe our tilted axis happened when our planet was hit by some other large celestial body billions of years ago. The rotation of the Earth on its axis causes daytime when the Earth faces the sun and nighttime when it faces away from the sun. When the figurative "point" of the axis directly points towards the Sun. This is called the solstice.

Because there is both a northern and southern point of the axis, the Northern hemisphere has its summer solstice in June and the Southern hemisphere has its summer solstice in December.

  1. A solstice is different from an equinox

Many people assume that the terms "equinox" and "solstice" are interchangeable. However, the equinox occurs when there are approximately equal hours of daytime and nighttime. The majority of the Sun's rays will shine right on the equator during the equinox. As the Earth continues in in its orbit, the Sun's rays will then shine more heavily on the northern or southern hemisphere of the planet depending on the time of the year. For example, in March equinox marks when the Sun transitions to shine more on the Northern hemisphere than on the Southern hemisphere. The reverse occurs during the September equinox.

If this has piqued your interest and you want to learn more about the Sun, be sure to watch tomorrow evening as we celebrate the Sun with a night of programming including the finale of Space's Deepest Secrets - When the Sun Attacks! Still need more Sun? Explore our online video right now!

 

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