Flames and smoke emerge from the Philadelphia Energy Solutions Refining Complex in Philadelphia, Friday, June 21, 2019. Experts say the explosions could have been far more devastating if deadly hydrogen fluoride had been released. Matt Rourke/AP hide caption
American aerospace engineer John Houbolt as he stands at a chalkboard in July 1962 showing his lunar orbit rendezvous plan for landing astronauts on the moon. NASA/LARC/Bob Nye/PhotoQuest/Getty Images hide caption
The World Health Organization says more than 1,650 people have died from the current outbreak of Ebola in the Democratic Republic of Congo. Al-hadji Kudra Maliro/AP hide caption
The astronauts of Apollo 11 train in various simulations. NASA hide caption
Secretary of Agriculture Sonny Perdue, shown here on Capitol Hill in April, announced last month that most staff from two USDA research agencies were being relocated to the Kansas City region. J. Scott Applewhite/AP hide caption
Diver swimming over Elkhorn Coral in the Florida Keys. Elevated nutrients as well as elevated temperatures are causing a massive loss of this iconic branching species in Florida. JW Porter/University of Georgia hide caption
Container ships and other maritime vessels currently run on pollutant-intensive heavy fuel oil. The world's largest container-shipping company, Maersk, has promised to make its operations zero carbon by 2050. Doing so will require using new fuels such as hydrogen. John Greim/LightRocket via Getty Images hide caption
(Left) The Apollo 11 command and service modules are mated to the Saturn V lunar module adapter. (Right) The Apollo 11 spacecraft command module is loaded aboard a Super Guppy aircraft at Ellington Air Force Base for shipment to North American Rockwell Corp. NASA hide caption
Native Hawaiians have objected to construction of the Thirty Meter Telescope for years. On Monday, about 300 protesters arrived to block workers from accessing the site on a mountain believed to be sacred land. TMT via AP hide caption