June 13 – 26, 2016
Mt. Washington — The numbers look good and the effect celebratory. The earliest sunrises of the year in our locale, 5:17 a.m. EDT (4:17 a.m. EST), began on June 8 and continue through the 21st. Summer Solstice, when the northern hemisphere is at full tilt towards the sun, occurs on June 20 at 6:34 p.m., while the Strawberry Moon reaches full phase earlier that day at 7:02 a.m.
Solstice, from the Latin sol + stit, translates to “sun stands still” or “stopped.” Earth seems to pause when it is at maximum axial tilt towards the sun, bringing about the longest days of the year during the period from the 18th through the 24th in our locale, 15 hours and 16 minutes from sunrise until sunset. On the 24th, the latest sunsets of the year begin and continue through July 1, while sunrise occurs almost a minute later every day.
All times represent small, incremental changes from one day to the next around the solstice. Since ancient times people have measured the sun’s changing relationship to Earth. We experience sustained maximum sunlight during the six-week period that spans from May 30 through July 13, when days are 15 hours or longer between sunrise and sunset and nights between 8 hours and 44 minutes, and 9 hours between sunset and sunrise. After the 13th, days shorten at a quickened pace.
Many months ago, I came across the intriguing figure eight image shown here. Known as an “analemma,” it is a record of the position of the sun in the sky photographed at the same time every day for a year. I was amazed and curious and thought it would be a fitting illustration for a solstice edition of “Eyes to the Sky.” I filed it away until last week, when I began to research how to understand and explain the mind-boggling figure eight, the peak of which shows the summer solstice and the base the winter solstice.
If we start with our observations of the dramatic changes of the position of the sun from week to week along the horizon at sunrise and sunset, and its changing arc in the sky from solstices to equinoxes, we begin to understand the effect of Earth’s axial tilt on the sun’s position. But that is linear, not a rolling, intersecting curve. I couldn’t find “analemma” in the indexes of my astronomy textbooks, and articles on the Internet did not unlock the mystery. I’d studied with astronomer Bob Berman, who teaches in our region and leads astronomy excursions around the world. I sent a query to him and received a step-by-step explanation. When I conveyed my appreciation to him, he sensed that I was still pondering the mystery of the analemma and not in full possession of an astronomical understanding of it. I will leave the beauty and mystery with you, thanks to Skyman Bob:
Explaining it truly requires a chalkboard at least. I think it’s impossible to convey using only words, which is why I’ve never chosen it as a topic in all my 40 years of writing articles for Discover, Astronomy, and all the rest. Even when I taught college astronomy courses I ignored it because people have too much trouble relating that “figure eight” to Earth’s orbital eccentricity, axial tilt, Kepler’s second law, and how all those things end up producing this tangible sky pattern when time exposures of the Sun’s daily position at local noon are viewed.
Resources:
https://earthsky.org/todays-image/todays-image-analemma-2013
https://www.space.com/31567-sun-analemma-figure-eight-sky-photo.html
