A "blog" is short of "weblog", a sort of online diary - at least, that's how they started out; nowadays, they can consist of just about any format. David Brin is a famed SF author (and slightly less famous Professor of Astrophysics at UCSD); his blog (davidbrin.blogspot.com), entitled "Contrary Brin", discussed politics (he's usually pigeonholed as libertarian, but has several disagreements with the Libertarian Party, and holds that political beliefs should not be plotted on a single line, but charted in at least two dimensions), the latest in scientific advances, transhumanism and the Singularity, and whatever else strikes his fancy at the moment. (He has written interesting deconstructions of Star Wars and the Lord of the Rings trilogy, both novel and movie; sadly, since they have been recently collected into books, his online links now only connect to truncated versions, that cut off before he really gets going.)
The Tacitus that posts there is one of the reasonable conservatives that Brin so enjoys discussing matters with - someone who is willing to back up his views with actual data, rather than merely parroting the talking points of Fox News (largely owned by Rupert Murdoch, founder of the Weekly World News, and the House of Saud, so Fox's fierce defense of an oil-based economy is hardly surprising...).
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Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.