Light 01: Stars

Welcome to the 2023 Advent Calendar, which this year is just a list of things that light up all pretty. Previous entries are here. If you enjoy this and want to encourage me to bang more things out on a keyboard, consider supporting my Patreon, or sending something off of my Christmas list. If you'd rather support my spoiled pets, their Ratmas list is here. If you want to spend money but not on me, you can direct your donations to Mainely Rat Rescue, who handles rescue and foster operations for rats, mice, gerbils, guinea pigs, and other small mammals in the New England area, or the MSPCA, where my critters got their medical care before I found a good exotics vet, and where I picked up Koda and Yogi. 

Enjoy your trip through the cavalcade of things that go blinky-blink in the dark!

In the beginning, there were stars.

Though from Earth, they seem to be tiny, twinkling lights, most of the stars we can see are about the size of our own sun -- a million kilometers in diameter -- or larger. They seem akin to crystals, in our minds, a solid substance that refracts light; in truth, they're closer to clouds, motes of matter that attract each other through the subtle force of gravity until such a large collection is achieved that atoms begin to cleave together, a type of nuclear reaction called fusion that we humans have only recently achieved.

Despite this, the light they emit comes from sheer incandescence. Anything glows when you get it hot enough. Stars are, in some narrow sense, just like light bulbs. The wavelengths a material emits -- and hence the color we perceive -- depend on just how hot it is. The hotter they are, the bluer they get. Red Betelgeuse, in the constellation Orion, is just about 3000 K; its neighbor, the comparatively blue Bellatrix, is almost 30000 K. 

Although many of the constellations in which we have traditionally grouped the stars are of Greco-Roman origin, described by Ptolemy in his Almagest, 14 of the 88 currently recognized by the IAU were defined as late as the 18th century, and include such modern shapes as the Telescopium (telescope), Microscopium (microscope), and Horologium (pendulum clock). Other cultures have other names, but have often picked the same cluster of stars. The collection of bright star in Taurus, known in the West as the Pleiades, were called Mitsuraboshi, and later Subaru, in the astronomical texts of Japan.

One of the most prominent constellations in winter, where I live in North America, is the aforementioned Orion, that rises just over the horizon about the time the school year starts. When I lived in the desert southwest, I used to watch for Orion to come back as a sign that the weather might soon be less miserably hot. You can see a map of the sky over Boston thanks to the local Museum of Science, who posts a monthly guide to spotting the constellations.