A first magnitude star is __________.

Correct Answer: Option A — 2.5 times as bright as a second magnitude star

The stellar magnitude scale is logarithmic, where a difference of one magnitude corresponds to a brightness ratio of approximately 2.512. Therefore, a first magnitude star is defined as being 2.5 times brighter than a second magnitude star, a fundamental principle of celestial navigation and astronomy documented in the Nautical Almanac.