Mare Imbrium’s Golden Handle

On Tuesday night, December 10, the terminator on the waxing gibbous moon will cross Sinus Iridum, the Bay of Rainbows. The circular 155 mile (249 km) diameter feature is a large impact crater that was flooded by the same basalts that filled the much larger Mare Imbrium to its east – forming a round bay encircled on the north and west by the prominent Montes Jura mountain range. The “Golden Handle” effect, produced when sunlight strikes the mountain peaks while the floor of the bay remains dark, will appear for observers in the Americas. With each passing hour, more of the mountains will become illuminated, brightening the handle.