The correct answer is B) comprises two stars that appear close together. A double star is a visual binary system, where two stars appear close together in the sky and orbit around a common center of mass. This is due to the alignment of the stars from our perspective on Earth, rather than an actual physical connection between the two stars. The other answer choices are incorrect because: A) has no relation to the definition of a double star, C) describes a variable star that brightens and fades, and D) is not a defining characteristic of a double star system.