Now and then I run across this sort of expression: "Bigger by several orders of magnitude." But what does that mean? Well, of course, it means "a whole lot bigger," but what is magnitude here (besides a cliche)?
The term has its source in astronomy, and my old Webster's Second defines it in this fashion: "The brightest stars are represented by the lowest (even zero) numbers; thus the brightest celestial body, the sun, is of -26.7 stellar magnitude; Sirius, a very bright star, is 1.6. The decimal magnitudes from -1.4 to 1.5 correspond to the former designation first magnitude; 1.6 to 2.5 second magnitude, and so on. Only stars of the sixth magnitude and brighter are visible to the naked eye."
The point is that when you leave astronomy, you also leave this precision, and the term "magnitude" becomes cloudy. Better to say "four times bigger." Or even "a whole lot bigger." Leave magnitudes to the star-gazers.
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Reading this forced me to do some research. The larger the number, the dimmer the star. The difference in one order of magnitude is 2.5 times brighter. If the difference in magnitude is greater than one order, raise 2.5 to the difference in magnitudes to find the relative brightness between the two objects. FYI, the Sun is more than 96 billion times brighter than Sirius. That's a whole lot brighter.
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