Terminology: Constellations and stars

One of the things I love about astronomy is you don’t actually need to know anything to appreciate the night sky. But if you want to communicate with others about what you saw or learn what’s out there, you have to have names.

Ever since humans have seen the stars, they’ve seen patterns. These patterns are called asterisms and they can be whatever you want. Some are common and have established names, such as the Big Dipper and Orion’s Belt. It’s important to remember that even though stars appear close to each other in the sky, they’re (usually) not actually connected. Since the stars are so distant, they all look equally far away, but they’re not. It would be like standing in New York City and thinking that because Chicago and San Francisco both lie in the same general direction, that they were closely connected.

Ptolemy formalized 48 of these as constellations. The International Astronomical Union (the international authority for astronomy) modified and expanded this list (including adding constellations that can only be seen from the southern hemisphere) into the modern official 88 constellations. Furthermore, constellations are now defined as areas of the sky, not as patterns of stars. This means that every point in the sky is part of some constellation. The bright stars may form patterns that help us to identify it, but they are not the constellation per se. I like to think of the stars as cities, and the constellations as states or countries. In the United States, some states have several large cities, others may have none. But every point in the United States is part of some state.

Star chart of Orion

Star chart of the constellation Orion. Note that the Orion includes the entire unshaded area, not just the bright stars and connecting lines. The Greek letters are Bayer designations (see below). (IAU/Sky&Telescope/Wikipedia)

The names of stars are bit more complex, since there are an estimated 3 sextillion stars in the observable universe (3 × 1023, or almost a trillion trillion stars)! Clearly, we need some naming scheme. I’ll normally use Johann Bayer’s method. To each star in a constellation, he assigned a lower-case letter from the Greek alphabet, usually following brightness and location characteristics. (After he ran out of Greek letters, he switched to lower-case Latin letters — our alphabet — and then upper-case letters). In his designation, the name of the star consists of the letter followed by the constellation name in the “genitive case” (a possessive form). Either the Greek letter can be used or it can be spelled out as an English word, and either the full constellation name or the standard three-letter abbreviation can be used. So for example, take Rigel, in the constellation Orion. This star will be called Beta Orionis, or β Orionis, or β Ori for short. Many stars also have their own names (like Rigel!). For the twenty or so brightest stars, their individual names are commonly used, but for the rest, Bayer designations are most common. There are stars that Bayer didn’t list, and for those I’ll use John Flamsteed’s names: they’re similar to Bayer’s method, but use a number instead of a Greek letter (for example, 40 Eridani, one of the stars in Eridanus).

For a more thorough discussion, see Sky & Telescope’s excellent Names of the Stars.

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Guitar Music

I love live music, though most of the time I have to settle for recorded music. I really enjoy watching the video clips uploaded to YouTube that people make of themselves performing music. While surfing the “related videos” from one of mine, I came across this incredible guitarist:

His name is Adrian Holovaty and apparently he’s from Chicago. He has several really good videos up there, though it looks like he’s set most of them so that embedding them is not allowed. So here are links to a few of my favorites:

More on the Environmental Costs of Eating Meat

Livestock’s high energy costs See full-sized image or accompanying article. Credit: Bill Marsh/New York Times.

An article in the New York Times last week further explores the costs that consuming animals has on the environment. (Please see also my previous post, “Vegetarianism vs. Meat-Eating and Global Warming”.)

Here’s a short excerpt:

…But consider: an estimated 30 percent of the earth’s ice-free land is directly or indirectly involved in livestock production, according to the United Nation’s Food and Agriculture Organization, which also estimates that livestock production generates nearly a fifth of the world’s greenhouse gases — more than transportation. To put the energy-using demand of meat production into easy-to-understand terms, Gidon Eshel, a geophysicist at the Bard Center, and Pamela A. Martin, an assistant professor of geophysics at the University of Chicago, calculated that if Americans were to reduce meat consumption by just 20 percent it would be as if we all switched from a standard sedan — a Camry, say — to the ultra-efficient Prius. …

The only way we can make environmentally friendly changes is to be informed of the impacts those choices will have. This thought-provoking article helps to show just how our food choices can drain resources and contribute to pollution in varying amounts.

So if you’re thinking about purchasing a more fuel-efficient car or trying to think of what else you could do to help the planet, cutting back on meat is another option. In addition to the obvious health benefits and improvements in animal welfare, you can now add conservation of water, ameliorating climate change, and numerous other factors to reasons to reduce your consumption of meat.

(Thanks to my sister for sharing this article with me.)