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)

NASA’s Swift satellite recently detected a growing flow of high-energy X-rays from somewhere near the center of our galaxy. The outburst, pictured in this illustration, was produced by a rare X-ray nova and announced the presence of a previously unknown stellar-mass black hole. (Image: NASA)

A school of Kokanee Salmon returns to the streams from which they were hatched. There, they select a mate, spawn and die. As the salmon make their annual fall migration, both sexes turn from their usual silver/blue color to a brilliant red. (Photo: United States Forest Service)

This image from the right Mast Camera (Mastcam) of NASA’s Mars rover Curiosity shows sand and dust lifted by the rover’s first use of the scoop on its robotic arm. (Photo: NASA)

A 700kg crocodile called Rex calmly waits just beneath the water’s surface for some food after coming out of a three-month hibernation at the Wild Life Sydney Zoo in Sydney, Australia. (Photo: AP)

No, these aren’t miniature UFOs. The tiny cube-shaped satellites were released into space from the International Space Station’s Kibo laboratory. One of these little CubeSats was developed by student interns at San Jose State University and will be used for a communications experiment (Photo: NASA)

The interior of the neutrino detector at Daya Bay in the People’s Republic of China, where a multi-national team of researchers from China, the United States, Taiwan, and the Czech Republic are studying neutrino oscillations. Neutrinos are electrically neutral elementary subatomic particles that can travel through great distances of matter without being affected by it. (Photo: Lawrence Berkeley National Laboratory)

This combined image from NASA is of the Helix Nebula, which has also been called the “Eye of God.” At the nebula’s heart is a dying star. In its death throes, the star’s outer layers unravel into space and are set aglow by powerful ultraviolet radiation pumped out by its hot stellar core. (Photo: NASA)

A monarch butterfly stops for a rest during its fall migration. The butterfly can journey up to nearly 5,000 km to its winter home in Mexico or Southern California. In the spring, they make another epic trip as they return to areas up north. (Photo: USDA)

This time-exposure photo shows the Falcon 9 SpaceX rocket lifting off from the Cape Canaveral Air Force Station in Cape Canaveral, Florida. The rocket, with its Dragon space capsule payload, just made its first commercial delivery of supplies to the International Space Station. (Photo: AP)