Solar prominence imaged Dec. 6, 2010, with Jupiter and Earth images superimposed to demonstrate the size. Image courtesy of NASA Goddard Space Flight Center, Solar Dynamics Observatory

EYES TO THE SKY: Summer Solstice, June 20, 2020

Outdoors, we experience the majesty of the Sun’s trajectory from sunrise at its extreme northeast reach, climbing to what seems to be the top of the sky at midday and then arcing to set at its extreme northwest position on the horizon.

June 15 – 28, 2020

Mount Washington — Every day is Sun day during the month of June, when the Sun is up for over 15 hours and darkness prevails for less than nine hours. The longest days of the year occur as Earth reaches the point in its orbit when the North Pole is tilted closest to the Sun, known as the summer solstice. This year, astronomers calculate that the solstice occurs Saturday, June 20, at 5:44 p.m. According to my pencil-on-paper figuring from Starry Night* data, which is offered to a 10th of a second, day length at our location on Friday the 19th is three seconds shorter than on the solstice and the 20th comes in at one second longer than on Sunday the 21st.

The chart below provides a picture, in numbers rounded to the minute, of markers in the progress of the day of the solstice. It is a useful guide until the end of June, given that day-to-day variations are in seconds.

Image courtesy Old Farmer’s Almanac

Stephen Schneider, professor of astronomy, University of Massachusetts Amherst, adds to our understanding with this observation: “The sun’s angle relative to Earth’s equator changes so gradually close to the solstices that, without instruments, the shift is difficult to perceive for about 10 days. This is the origin of the word solstice, which means “solar standstill.”

The North Pole is tilted toward the sun. There are 24 hours of daylight north of the Arctic Circle. There are 0 hours of daylight (24 hours of night) south of the Antarctic Circle. At the equator, the days are always 12 hours. Image courtesy University of Arizona Atmospheric Sciences

The drawings from the University of Arizona** vividly depict the arc of the Sun rising and setting on the summer solstice at various latitudes. Great Barrington’s latitude is 42 11.6′ N; longitude 73 21.3′W. Great Barrington falls between the arcs that describe Minneapolis and Tucson. Outdoors, we experience the majesty of the Sun’s trajectory from sunrise at its extreme northeast reach, climbing to what seems to be the top of the sky at midday and then arcing to set at its extreme northwest position on the horizon.

The detail below is a guide to viewing solstice-time sunrises and sunsets.

If you look east from position X in the picture, you won’t see the sun because you won’t be looking back along the ray of light coming from the sun. You must turn to the north. The sun rises in the northeast on the summer solstice and sets in the northwest. Image courtesy University of Arizona Atmospheric Sciences

Resources

*https://www.starrynight.com/ProPlus7/index.html
**http://www.atmo.arizona.edu/students/courselinks/fall07/nats101s31/lecture_notes/sunpaths.html

https://en.wikipedia.org/wiki/Solar_Dynamics_Observatory
https://en.wikipedia.org/wiki/Solar_prominence
https://commons.wikimedia.org/wiki/File:Sun_earth_jupiter_whole_600.jpg

How big the Sun https://space-facts.com/how-big-is-the-sun-million-earths/

https://www.space.com/40926-summer-solstice-2018-explained-by-astronomer.html

https://www.almanac.com/astronomy/sun-rise-and-set/zipcode/01230/2020-06-20
https://www.almanac.com/content/first-day-summer-summer-solstice