Summer Solstice

Equinoxes and solstices are astronomical markers that divide a year. The Earth’s axis is tilted to the plane of its orbit around the Sun, as it moves around the Sun twice in that orbital period the tilt of the Earth is zero relatively comparing to the Sun, in which the Earth’s axis is neither points towards or away from the sun, these events are called equinoxes. There is a point as the Earth moves around the Sun, first one pole and then the other are tilted toward the Sun, these are called solstices.

There are no fixed dates and it slightly varies every year and may occur a day earlier or later depending on the time zone, because equinoxes and solstices are dependent to the position of the Sun. Within a year, equinoxes occur between March 19 and 21, and between September 22 and 24. While for solstices occur between June 20 and 22, and between December 20 and 23.

Speaking of astronomical markers, today’s date marks a significant event, the summer solstice of the Northern Hemisphere and winter solstice for the Southern Hemisphere.

It is the 21st of June

Solstices are the days of the year in which the Sun rises to its highest point in the sky in either the Northern or Southern Hemisphere. The summer solstice occurs when the Sun rises to what appears to be its highest point in the hemisphere of the observer, and the winter solstice when it reach its highest point in the opposite hemisphere. It changes so gradual that shift is difficult to observe for about 7 to10 days, thus the origin and meaning of the word solstice, which have the notion of “solar standstill.”

On June 21st, the North Pole is tilted toward the Sun by its greatest amount, of 23.5 degrees from the perpendicular to the orbital plane. The sun sill appear farthest north observing from earth, then the angle of tilt reverses until six months later, in which the sun will reach its southern extreme. This brings the day of longest daylight and shortest night in the Northern and shortest daylight and longest night in the Southern Hemisphere.

Significance of Summer Solstice

The summer solstice in June signals the official beginning of summer in the Northern Hemisphere. This region gets more exposure to direct sunlight while raises temperature leading to activation of certain reproductive activities from both plants and animals. For human society, the sign of changes of the season is a useful indicator to begin or end certain communal agricultural activities like harvesting and mating of livestock. And most traditions and celebrations surrounding summer solstice leans towards fertility and marriage.

For more than 5,000 years, ancient human civilizations have been drawn to record the north to south movement of the Sun, evident by the large intricate monuments like Stonehenge in England, Chankillo in Peru and Karnak in Egypt. Human beings ability to utilize the Sun and the Moon, and other celestial bodies to organize a clock, calendar and other means to measure time contribute to the survival and progress of human civilization.

As always enjoy your summer break!

References

1. The Editors of Encyclopedia Britannica. (2013). Encyclopedia Britannica. [Website]. Retrieved from https://www.britannica.com

2. Royal Museums Greenwich. (n.d.). Equinoxes and Solstices [Blog Post] Retrieved from https://www.rmg.co.uk/discover/explore/equinoxes-and-solstices

3. Resnick, B. & Plumer, B. (2018, June 21). The summer solstice is here: 6things to know about the longest day of the year. [Blog Post]. Retrieved from https://www.vox.com/science-and-health/2018/6/19/17479094/summer-solstice-2018-june-21

4. Scheneider, S. (2018, June 21). What is the Summer Solstice? An Astronomers Explains. [Blog post] Retrieved from https://www.space.com/40926-summer-solstice-2018-explained-by-astronomer.html