Tucker invites Sam and Gregor to view a "new moon" through a telescope when they are at the Amity Park Observatory at night. A new moon is on the daylight side of the Earth, and is nearly impossible to view because of the sun's glare. Tucker would know this.
When Danny's listing off the things Gregor has in common with the Guys in White, one of the items is that they both have white hair. However, the Guys in White are bald.