Artist’s concept of a new view of the Milky Way. Scientists have discovered the Milky Way’s elegant spiral structure is dominated by two arms wrapping off the ends of a central bar of stars. Our galaxy was previously thought to possess four major arms. (NASA)

Native to Madagascar, this is an indri, one of the largest living lemurs in the world. (Meredith Barrett)

This is a Spallation Neutron Source cavity assembly in the clean room the Thomas Jefferson National Accelerator Facility in Virginia. It’s a piece of a particle accelerator scientists use to provide the most intense pulsed neutron beams in the world. (Jefferson Lab)

NASA will use this spacecraft, seen here with its solar panels deployed  in a clean room at Lockheed Martin in Sunnyvale, California, for its Interface Region Imaging Spectrograph (IRIS) mission scheduled for launch this April. (Lockheed Martin)

Immune system cells, called macrophages, normally engulf and kill intruding bacteria but sometimes the microbes, shown in red, find a way to escape into the interior of the cell where it can multiply and invade other cells. (Miao lab, UNC School of Medicine)

A large male purple marsh crab (Sesarma reticulatum) clips cordgrass with its claws. These crabs are nocturnal and typically live in burrows during the day to stay moist and avoid predators. (Tyler Coverdale)

This is a single five-minute exposure taken recently in Buenos Aires on an Argentinian summer night. It shows not only Earth clouds but starry clouds, the pinkish glow of the Carina Nebula and Small Magellanic Clouds. The line arcing from the center of the right side to the lower left is the orbiting International Space Station. (Photo & Copyright: Luis Argerich)

Before workers with NASA’s US Antarctic Program are sent into the field, they must first undergo training to endure the harsh Antarctic conditions. Here’s a look at their training camp site, set up on the Ross Ice Shelf ,the largest ice shelf of Antarctica. ( NASA)

Found in the waters surrounding the Philippines, a moray eel poses for a photo. (M. J. Costello)

After four months aboard the International Space Station, three Expedition 33 crewmembers returned to Earth in their Soyuz spacecraft, making a rare night landing in a remote area of Kazakhstan. (NASA)

Antarctica’s Sheldon Glacier with Mount Barre in the background. This photo was taken by scientists participating in a new NASA/British Antarctica Survey studying the effects of climate change on Antarctic sea ice cover. (British Antarctic Survey)

The Large Underground Xenon (LUX) detector is an important tool in scientists’ search for dark matter, one of nature’s most elusive particles.  This is a top-down view of the copper photomultiplier tube mounting structure, a key component of the detector. (Lawrence Livermore National Laboratory)

An adult female walrus sits on an ice floe just off the Eastern Chukchi Sea in Alaska. (S.A. Sonsthagen/USGS)

The Sun recently experienced two prominent eruptions, which occurred one after the other over a four-hour period. Fortunately, the expanding particle clouds shooting into space weren’t directed at Earth. (NASA)

A view of the countryside in Binghamton, NY as seen from inside a US National Weather Service radar radome (which protects radar components from the elements). The weather radar was recently taken offline so that repairs could be made. (NOAA/NWS)

Titan, the world’s most powerful and fastest supercomputer, is located at the Oakridge National Laboratory in Tennessee. Titan’s computational capability is on par with each of the world’s 7 billion people being able to carry out 3 million calculations per second. (Oakridge National Laboratory)

A group of galaxies glows like fireflies on a dark night in this image snapped recently by the Hubble Space Telescope. (NASA)

A cluster of lightning over a US National Severe Storms Lab Probe minivan which measures weather statistics as it travels through storms. (NOAA)

Scientists at the U.S. Department of Energy’s (DOE) Ames Laboratory are working to more effectively remove a rare earth element (group of closely related metallic elements) called neodymium from the mix of other materials in a magnet. Here rare-earth magnet scraps are melted in a furnace with magnesium. (DOE/Ames Laboratory)