"Like any scientific field, it has its own jargon and buzzwordsand terms with meanings that can be not only odd but downright counterintuitive. The most obvious one is astronomers' use of the word metal to mean any element heavier than helium. Lithium? Metal. Oxygen? Metal. Carbon? That's a metal, too, as far as astronomy is concerned. Using a single term to cover these heavier-than-helium elements."
"The words that really irritate me are not only confusing but also obsolete. These are terms we should dump in favor of others that better reflect our more modern understanding. A great example of this is Population I, II and III starsthese really refer, in order, to stars with more metals in them, stars with fewer metals and stars that were the very first in the universe, which is ridiculously confounding. But to our credit, astronomers do sometimes drop terms when they become outdated."
"It can just take a long time. For example, I remember reading articles in older books about spiral nebulas when I was much younger. Nebula is a fairly generic term; it's Latin for fog and means any sort of diffuse deep-space object we see in the sky. Some, such as the great Orion Nebula, have little overall shape, while others, such as the Ring Nebula, are highly structured. We now know these are all immense clouds of gas and dust,"
Astronomy uses specialized jargon with terms that can be counterintuitive. Astronomers use the word metal to denote any element heavier than helium, so lithium, oxygen and carbon are all classified as metals. Lumping heavier-than-helium elements into one category simplifies calculations because the universe is dominated by lighter elements. Historical classification systems such as Population I, II and III refer to stars with varying metal content and the earliest stars, which creates confusion. Some obsolete terms persist but are occasionally retired over long timescales. Nebula originally meant any diffuse deep-space object; many nebulae are enormous clouds of gas and dust with varied structures and origins.
Read at www.scientificamerican.com
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