Under dry skies and against a chromatic sunset, more than two dozen turned out late Saturday afternoon December 21 to engage with retired Lawrence Hall of Science educator and planetarium director Alan Gould about the mysteries of the Winter Solstice.
The puzzle wasn’t why the Solstice happens. Gould wasted no time toppling the straw man that it had to do with the sun-earth distance. No: at the Winter Solstice in the Northern Hemisphere, the earth is actually closer to the sun than the rest of the year. The reason for the seasons is the earth’s tilt. Its north/south axis is 23.5 degrees off vertical relative to the plane of the earth’s orbit. The earth’s axis always points (approximately) at the North Star. This means that in the northern winter, the earth presents its bottom half to the sun, so that it’s summer below the equator; and in the northern summer, the sun favors the earth above the belt, while the lower half gets the sun on shortened time.
No, the mystery is how come the latest sunrise and the earliest sunset don’t both happen on the Solstice, which is the shortest day. Instead, the latest sunrise occurs Jan. 3-8, for six days in a row, while the earliest sunsets happen for a week in early December (December 4-10). The 4:53 pm sunset that happens on Solstice also occurred December 2. Why? Well, Gould explained, “it’s complicated.” It had something to do with the earth’s deviation from its circular orbit, which also throws off the timing of solar noon relative to average solar noon. In fact, it makes all earthly clocks’ timekeeping partly fictitious. Another factor is the sun’s analemma, the lopsided figure eight that it traces in the sky as the year progresses. Gould posted key points of the explanation, along with other Solstice material, on his planetarium website, here. There’s at least one website that goes into it more deeply.
Gould also mentioned some of the numerous Winter Solstice celebrations — overt or masked — held around the world: Saturnalia (Ancient Rome), Juul (Scandinavia), Shab-e Yalda (Persia), Inti Raymi (Peru, Ancient Incas), Dongji (Korea), Dong Zhi (China), Toji (Japan), Kwanzaa (African-American), Soyal (Hopi), Shalako (Zuni), Newgrange (Ireland) and of course, Hanukkah and Christmas.
The site of Gould’s talk, as he pointed out, is embedded with stonework that blends the astronomical and the celebratory. Peaked stones point to the location of sunset and sunrise at the solstices and the equinoxes. Four horizontal stones commemorate the virtues of the United Farm Workers movement that Cesar Chavez and Dolores Huerta launched: Hope, Tolerance, Determination, and Courage.