## The Pogson Method of Estimating Brightness

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Norman Pogson is a well-known variable-star observer from the nineteenth century. He developed a procedure that differs from Argelander's method in that each step is determined to be precisely OTl. This method requires you to compare a variable star with a single comparison star using a previously memorized interval of O'Vl. You then observe the variable again, using a different comparison star. The variable's magnitude is deduced later. Your first observation might be recorded as "A - 5," indicating that the variable star is five steps, or 0m5, fainter than the brighter comparison star. Since you have already memorized what a tenth of a magnitude, or step, looks Like, this observation is independent of the next, which considers the fainter star. In the second observation you might say "B + 4," meaning that the star is four steps brighter than the comparison star. Later, we would find out that A = 11.4, thus A - 5 = 11.9. If B were equal to 12.3, the B + 4 would also equal 11.9. Remember that a star gets fainter as its magnitude number gets higher.

The difficulty with this method is exactly memorizing the 0111 increments for your comparison stars.