(Roughly) Daily

“Oh dark, dark, dark, amid the blaze of noon, irrevocably dark, total eclipse without all hope of day”*…

Today is the occasion of an annular eclipse, which will pass through eight U.S. states before crossing the Gulf of Mexico and to transit Mexico, Guatemala, Belize, Honduras, Nicaragua, Costa Rica, Panama, Colombia, and Brazil. While some people in the Western Hemisphere will witness a “ring of fire” during the eclipse, many more will experience the phenomenon of crescent sunlight. Rebecca Boyle has advice on how we might approach it…

… This Saturday, for some people in the Western Hemisphere, the Sun will disappear for a few minutes and appear to leave a flaming hole in the sky. Instead of a ball of fire, the Sun will transform into a ring of fire, a strange and wondrous sight. This is an annular solar eclipse, and it happens because the Moon is right smack in front of the Sun.

A solar eclipse only happens during new Moon phases, when we otherwise wouldn’t be able to see our nearest celestial companion. Though we get a new Moon every month, we do not get solar eclipses as often because of our satellite’s oddball path around the planet. Sometimes the Moon casts a shadow just above Earth, and sometimes just below. This weekend, the Moon’s shadow will fall onto Earth, just right for people in parts of the Western Hemisphere to see it.

The annular eclipse is a preview of a more incredible, rarer event next April, when a total solar eclipse will cross the continental United States. There is no experience on Earth like a total eclipse; make plans to see it, if you can. But this weekend’s “ring of fire” eclipse is an event you should try to see first (safely, with eclipse glasses), if you can get yourself into the western U.S. or parts of Central and South America. Here’s a map showing the eclipse path; if you can’t travel to see it in person, you can watch the eclipse online.

Eclipses happen because the Sun and Moon appear to be roughly the same diameter. The Sun is actually about 400 times larger than the Moon, but it is also about 400 times more distant, so they seem like the same size in our sky.

The Moon’s shadow forms two concentric cones, composed of an inner shadow called the umbra, where the sun is completely obscured, and an outer, broader cone called a penumbra, where sunlight still shines but it is partially blocked. The umbra can be seen in a narrow geographic ribbon across the Americas, and it’s where you will see a full eclipse; under the penumbra, which covers much of the western U.S., Central and South America, you will see a partial eclipse.

Like the gears of a clock, a combination of precise positions and movements initiate an eclipse of the Sun. As Earth spins, day breaks. The Sun and Moon appear to trace a path across the sky. The Sun is not moving (at least not perceptibly); Earth’s rotation makes the star’s position change. The Moon is moving around us while the Earth rotates, so it seems to move too, but it appears to go slower than our star. The partial solar eclipse begins as the Sun catches up to the Moon’s position in our sky. On Saturday morning around 8:06 a.m. Pacific time, people in Eugene, Oregon, will be the first to see the Moon appear to take a bite out of the Sun. The bite will get progressively bigger until the full annular eclipse begins at 9:16 a.m. Pacific time.

The annular eclipse only lasts about four minutes (depending on your precise location under the Moon’s shadow) but the partial eclipse, which will be visible over a much wider geographic area, lasts about an hour and 15 minutes before and afterward. During this phase, shadows cast by objects on Earth will change in unusual ways. One lovely place to be during a partial solar eclipse is underneath a tree, if you can find an evergreen or a deciduous tree that has not dropped its leaves yet. Look at the ground. In the dappled light, you will see crescents everywhere: the crescent Sun.

Sunlight is the heavens reaching down to touch us right where we stand; I think about this when I step into the light. But crescent sunlight is the Moon joining this experience. Its darkness, rather than its light, reaches out to touch us, too…

An informative and lyrical guide to today’s eclipse: “During an Annular Eclipse, Look to the Shadows,” from @rboyle31 in @atlasobscura.

* John Milton, Samson Agonistes


As we don’t look directly, we might recall that on this date in 1609, Galileo (who has claim to the titles Father of observational astronomy, modern-era classical physics, the scientific method, and modern science) put the telescope to use in his astronomical work. Upon hearing (at age 40) that a Dutch optician had invented a glass that made distant objects appear larger, Galileo crafted his telescope. He continued to improve his device, ultimately achieving 30X magnification, and recorded his observations of the Moon, the moons of Jupiter, the Phases of Venus, Sunspots, The Milky Way, and more. He published his initial telescopic astronomical observations in March 1610 in a brief treatise entitled Sidereus Nuncius (Starry Messenger).

Telescopes were also a profitable sideline for Galileo, who sold them to merchants who found them useful both at sea and as items of trade.

Galileo’s “cannocchiali” telescopes at the Museo Galileo, Florence (source)

Written by (Roughly) Daily

October 14, 2023 at 1:00 am

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