The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21, 2016, as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, 62 feet below the surface of the Atlantic Ocean. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. http://www.nasa.gov/sites/default/files/thumbnails/image/cn7b4dnwgaar5ph.jpg

This NASA/ESA Hubble Space Telescope image reveals the vibrant core of the galaxy NGC 3125. Discovered by John Herschel in 1835, NGC 3125 is a great example of a starburst galaxy — a galaxy in which unusually high numbers of new stars are forming, springing to life within intensely hot clouds of gas. http://www.nasa.gov/sites/default/files/thumbnails/image/hubble_monday_07252016.jpg

NASA’s Scalable Convergent Electric Propulsion Technology and Operations Research (SCEPTOR) project has reached a critical milestone, where the electric propulsion integration and conversion of the Tecnam P2006T aircraft into the X-57 will commence. http://www.nasa.gov/sites/default/files/thumbnails/image/afrc2016-0212-109.jpg

An unusual celestial object called CX330 was first detected as a source of X-ray light in 2009. It has been launching “jets” of material into the gas and dust around it. http://www.nasa.gov/sites/default/files/thumbnails/image/pia20700.jpg

The blue dots in this field of galaxies, known as the COSMOS field, show galaxies that contain supermassive black holes emitting high-energy X-rays. http://www.nasa.gov/sites/default/files/thumbnails/image/pia20865.jpg

On July 21, 2016, Expedition 48 Commander Jeff Williams of NASA shared this photograph of sunglint illuminating the waters of the Chesapeake Bay, writing, "Morning passing over the Chesapeake Bay heading across the Atlantic." http://www.nasa.gov/sites/default/files/styles/full_width_feature/public/thumbnails/image/iss048-e-28526.jpg

Acadia National Park is one of the most visited parks in America, drawing more than 2.5 million visitors per year to the craggy, jagged coast of Maine. The park is celebrating its 100th anniversary in 2016. On September 6, 2015, the Operational Land Imager (OLI) on the Landsat 8 satellite acquired these images of the park and its surroundings. http://www.nasa.gov/sites/default/files/thumbnails/image/acadia_oli_2015249_lrg.jpg

A team of NASA scientists and engineers is poised to realize a lifetime goal: building an instrument powerful and accurate enough to gather around-the-clock global atmospheric carbon-dioxide (CO2) measurements from space. Developers of the CO2 Sounder Lidar instrument snapped this photo during a field campaign over California and Nevada. http://www.nasa.gov/sites/default/files/thumbnails/image/dsc_1488_sciflt_south_of_elko.jpg

Engineers and astronauts conducted testing in a representative model of the Orion spacecraft at NASA’s Johnson Space Center in Houston to gather the crew's feedback on the design of the docking hatch and on post-landing equipment operations. http://www.nasa.gov/sites/default/files/thumbnails/image/p1010194.jpg

Neil A. Armstrong is photographed in the cockpit of the Ames Bell X-14 aircraft at NASA's Ames Research Center. Armstrong, the first man to walk on the moon, was born in Wapakoneta, Ohio, on August 5, 1930. http://www.nasa.gov/sites/default/files/thumbnails/image/7901650998_5b650b7976_o.jpg

An astronaut aboard the International Space Station adjusted the camera for night imaging and captured the green veils and curtains of an aurora that spanned thousands of kilometers over Quebec, Canada. http://www.nasa.gov/sites/default/files/thumbnails/image/iss030e110900_lrg.jpg

This false-color view from NASA's Cassini spacecraft shows clouds in Saturn's northern hemisphere. The view was made using images taken by Cassini's wide-angle camera on July 20, 2016, using a combination of spectral filters sensitive to infrared light at 750, 727 and 619 nanometers. http://www.nasa.gov/sites/default/files/thumbnails/image/7395_saturn_gill_infrared.jpg

Two cosmic structures show evidence for a remarkable change in behavior of a supermassive black hole in a distant galaxy. http://www.nasa.gov/sites/default/files/thumbnails/image/ic2497.jpg

The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite passed directly over Rio de Janeiro on Aug. 2, 2016, just prior to the opening of the Summer Olympic Games. On the left is an image from MISR's nadir camera; on the right, a map of aerosol optical depth. http://www.nasa.gov/sites/default/files/thumbnails/image/pia20885.jpg

In this 30 second exposure, a meteor streaks across the sky during the annual Perseid meteor shower Friday, Aug. 12, 2016 in Spruce Knob, West Virginia. http://www.nasa.gov/sites/default/files/thumbnails/image/nhq201608120002.jpg

Expedition 48 crew members Kate Rubins (left) and Jeff Williams (right) of NASA outfit spacesuits inside of the Quest airlock aboard the International Space Station. Rubins and Williams will conduct a spacewalk on Friday, Aug. 19, 2016, to install a new docking port that will enable the future arrival of U.S. commercial crew spacecraft. http://www.nasa.gov/sites/default/files/thumbnails/image/28111335603_7527bc33da_o.jpg

The remotely controlled Sally Ride EarthKAM aboard the International Space Station acquired this photograph on July 14, 2016, as the orbiting laboratory flew over Lake Powell and the border of Utah and Arizona. Located on the Colorado River, Lake Powell is the second largest artificial reservoir in the United States. http://www.nasa.gov/sites/default/files/thumbnails/image/ccfid_111329_2016196161113_image.jpg

A new look at the debris from an exploded star in our galaxy has astronomers re-examining when the supernova actually happened. http://www.nasa.gov/sites/default/files/thumbnails/image/g11.jpg

Welders inside a large liquid hydrogen tank for NASA's Space Launch System at the Michoud Assembly Facility in New Orleans are plugging holes left after the tank was assembled. http://www.nasa.gov/sites/default/files/thumbnails/image/maf_20160805_sf02_p_lh2_qual_fusion_welds-148.jpg

As NASA celebrates National Aviation Day, the agency's innovators are working to transform air transportation to meet the future needs of the global aviation community. The agency is embarking on a 10-year plan, New Aviation Horizons, that will see NASA field a number of experimental aircraft to demonstrate 21st century ideas for flight. http://www.nasa.gov/sites/default/files/thumbnails/image/afrc2016-0212-100.jpg