The figure-8 shaped curve is called an analemma. It’s a photo of the sun, taken every day at the same time, in this case 7:30 a.m. local time in Hong Kong. Matthew Chin created this analemma in 2014. He also add the Chinese solar terms, which comprise a calendar of 24 periods and climate, set up to govern agriculture in ancient China and referred to in China even now. Matthew wrote:
Due to cloudy or rainy days, the image may be taken before / after the solar term day and are marked +/- nd(ays).
That year’s two equinoxes on March 21 (0° longitude) and September 23 (180° longitude) correspond to the mid-points but not the cross-over point, on the curve.
While summer solstice on June 21 (90° longitude) and winter solstice on December 22 (270° longitude) are located at the top-left and bottom-right on the curve respectively.
The solar term days are listed as below (based on Hong Kong Time) for year 2014 by Hong Kong Observatory.
Thank you, Matthew!
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.