Bait-and-switch Memes

You enter the lecture hall excited about stars and planets, then BAM! The professor starts babbling about spectroscopy, parallax measurements, and relativistic redshifts! What you thought was going to be "oooh pretty space pictures" turns into "calculate the proper motion of this binary system using these 17 differential equations." The cosmic bait-and-switch strikes again! The stars may be billions of years old, but your enthusiasm for the class died in just 10 minutes.