Tom's comment about the Sun comes on a hot day, and demonstrates how he takes in information without understanding it:
"I read somewhere that the sun's getting hotter every year," said Tom genially. "It seems that pretty soon the earth's going to fall into the sun -- or wait a minute -- it's just the opposite -- the sun's getting colder every year."
(Fitzgerald, The Great Gatsby, mrbye.com)
Tom shows here that while he may have read some statistic about the Sun's temperature, and about the eventual fate of the Solar System, he has no idea what that fact means in the large scheme of things. It is, for Tom, nothing more than a comment for small talk. Tom is incapable of understanding the life-cycle of a star, or the Sun's routine heating and cooling activity, and so drops this sentence -- immediately contradicting himself -- because of the heat, not because he wants to inform. For Tom, the facts are barely more than a collection of syllables that make him sound smart, and he expects that the people around him are equally ill-informed.