Question 1436Navigation General

The correct answer is C) nova. A nova is a star that suddenly becomes several magnitudes brighter and then gradually fades over time. This sudden increase in brightness is caused by a thermonuclear explosion on the surface of a white dwarf star, which is part of a binary star system. The other answer choices are incorrect: A) double star - A double star is two stars that appear close together in the sky, but are not necessarily related. B) variable star - A variable star is a star that fluctuates in brightness over time, but not as dramatically as a nova. D) nebula - A nebula is a cloud of gas and dust in space, not a type of variable star.