What Is String Theory? Brian Greene Explains

The collection of 140,000 bat specimen at Smithsonian's National Museum of Natural History is providing a key resource for tracking the epidemic that is wiping out the world's bat population.

The Silent Killer Wiping Out This Small Species in America (2:35)

Years after all double eagles were supposedly destroyed, the Secret Service traces the reappearance of two of the rare coins back to a deal between jeweler Israel Switt and Mint cashier George McCann.

Why This 1933 Double Eagle Coin Will be Worth Millions (3:00)

Five hundred passionate Civil War reenactors gather every year to live in period tents, wear costumes and play out every step of the little-known battle.

Why 500 Men Gather in a Little-Known Louisiana Field (2:31)

Deep caves and secret tunnels provide the crocodile with a stealthy advantage in stalking its prey.(Courtesy of Paul Scofield)

Stealthy Crocodile Captures Unsuspecting Prey (2:13)

Sci-fi fan Gene Roddenberry was a freelance writer with a futuristic vision. He had high hopes for his script about a peacekeeping spaceship seeking new life forms.

How an L.A. Cop Wrote Megahit 'Star Trek' (2:34)

No one knows for certain why the Lalibela churches share many similarities with Judaism, but scholars propose a handful of holy theories.

Why the Town of Lalibela is One of Ethiopia's Holiest Sites (2:55)

In 1947, when a local rancher claimed to have found a flying saucer in his field, Roswell became the center of conspiracy theories and a tourist destination for anyone in search of little green men.

The Mysterious Roswell UFO Incident of 1947 (1:25)

From Frida Kahlo's passionate love letters sealed with a kiss, to watercolor notes from famous artists, let the Smithsonian's love letter collection inspire your handmade valentines.

A Secret Love Letter From Frida Kahlo's Extramarital Affair (1:29)

In 1860, aeronaut Thaddeus Lowe met with President Lincoln to discuss the possibility of using gas-filled balloons for military reconnaissance.

The Unusual Way Union Troops Spied on Confederates (3:08)