Question 1433Navigation General

The correct answer is D) exhibits a change in magnitude. A variable star is a star whose brightness (magnitude) fluctuates over time, either increasing or decreasing. This change in brightness or magnitude is the defining characteristic of a variable star. The other answer choices do not accurately describe what a variable star is. The other options are incorrect because: A) having a changing declination is not specific to variable stars, B) increasing in SHA (Sidereal Hour Angle) does not necessarily indicate a variable star, and C) being a red giant is a separate classification of stars, not the definition of a variable star.