Star Gazers (1987)

When Phil and Mike set out for a weekend of comet watching, they end up checking out more tail than comet. At their mountain cabin, their hefty telescope focuses on two luscious celestial bodies who explore each other's terrain, then are joined by a man who does a thorough probing of their crater. Later, the celestial bodies join Mike and Phil in their cabin for an outta this world oral orbit - then, their wives unexpectedly pop in for the rest of the weekend. No one does much comet gazing--they're all too busy studying the rings around Uranus, and shooting for the moon.