When summer heat comes to the Arara neighborhood in northern Rio, it lingers, baking the red brick and concrete that make up many of the buildings long after the sun has gone down. Luis Cassiano, who's lived here more than 30 years, says he's getting worried as heat waves become more frequent and fierce. In poor areas such as Arara, those who can afford air conditioning — Cassiano is one — can't always count on it because of frequent power outages on an overloaded system.

Highlights from a cometary trio that captured our imaginations.

NASA began the countdown Monday for humanity’s first launch to the moon in 53 years. The 32-story Space Launch System rocket is poised to blast off Wednesday evening with four astronauts. “Our team has worked extremely hard to get us to this moment,” said launch director Charlie Blackwell-Thompson.