The cover of National Geographic magazine opens the door to adventure and broadens horizons.

"'Come look,' it says. 'See what wonder the world contains,'" writes Chris Johns, the Society's chief content officer, in the preface to the newly published book National Geographic: The Covers.

In the course of its 126-year history, the magazine has published 1,465 covers. The first issue, published in 1888, featured a drab brown cover relieved only by black type. Color photography on a cover first appeared in 1959—a picture of an American flag. Since then readers have been treated to covers framed by superlatives—images more arresting, more moving, more telling, because the magazine's photographers are driven to make them so.

Every cover has a story behind the story. It may be a tale of creative initiative, or of working in dicey circumstances, or of the kind of luck that goes hand in hand with years of experience and wisdom.

Here are five iconic covers and how they came to be.

1. Smart Dog

Six dogs have appeared on the magazine's cover, but none sold more copies than Betsy the border collie for March 2008's "Animal Minds."

View Images National Geographic's March 2008 cover. Photograph by Vincent J. Musi, National Geographic Creative

Betsy, along with other animals featured in the story, like Azy the orangutan and Maya the bottlenose dolphin, are the superstars of the animal cognition world, photographer Vince Musi says.

To illustrate the story on animal intelligence, Musi chose to take their portraits rather than depict their behavior. As with human subjects, it took a little bit of coaxing and cooperation to get the perfect shot.

"I set the lights up, I try to sing to [the animals] a little bit, introduce them to some culture, often Frank Sinatra and sometimes Elvis Costello," Musi says in a video. "And I tell them everything I wanted to do."

Betsy, who was photographed in her hometown of Vienna, Austria, was one of the most cooperative animals Musi worked with, recounts photo editor Kathy Moran.

"After hours with the prairie dog, there was one usable shot," she says. By comparison, "Betsy was pretty easy."

2. The Hot Spring of Yellowstone

To capture the Grand Prismatic Spring at Yellowstone National Park for the August 2009 cover, photographer George Steinmetz stood on the skids of a helicopter. "I get kind of fearless with a camera," Steinmetz told National Geographic Proof. (Related: "Fellows in Yellow: The Men of National Geographic.")

View Images National Geographic's August 2009 cover. Photograph by George Steinmetz, National Geographic Creative

Park regulations prohibited its use, but his airborne vehicle of choice is actually a motorized paraglider, which he describes as a "leaf-blower with a kite overhead."

3. The Afghan Girl

Drawn to her famously haunting eyes, photographer Steve McCurry quickly made two shots of a 12-year-old girl in a refugee camp near Peshawar, Pakistan, for "Along Afghanistan's War-torn Frontier," the cover story of the June 1985 issue. (Related: "Leading Ladies: The Women of National Geographic.")

View Images National Geographic's June 1985 cover. Photograph by Steve McCurry, National Geographic

After her image appeared on the cover, she became known at the magazine as "the Afghan girl." In April 2002, McCurry found her living back in Afghanistan and took her photo again. Her name, we learned then, was Sharbat Gula. She was now married with three children, and she remembered the day the photographer took her picture.

Said McCurry: "I didn't think the photograph of the girl would be different from anything else I shot that day." But it was, and it became perhaps the most iconic, and certainly the most arresting, cover the magazine has ever published.

4. Tallest Trees

It took three weeks, 84 images, and a rope-and-pulley system to make the October 2009 cover, "The Tallest Trees." (Related: "By Air, Land, and Sea: National Geographic Explores Our World.")

View Images National Geographic's October 2009 cover. Photograph by Michael Nichols, National Geographic Creative

This particular giant was 300 feet (91 meters) tall and 1,500 years old. To make the image, photographer Michael "Nick" Nichols combined a camera with a pulley system rigged between neighboring trees, then remotely triggered the shutter with his laptop.

The best 84 were stitched into a composite for a pullout gatefold. Three years later, Nichols photographed another tall tree for the December 2012 cover: a 3,200-year-old redwood tree nicknamed the President.

5. Portrait of the Artist as a Young Ape

Koko the gorilla is both subject and photographer of the October 1978 cover story, "Conversations With a Gorilla." (Related: "Fur, Feathers, and Scales: National Geographic's Majestic Animals.")

View Images National Geographic's October 1978 cover. Photograph by Ronald H. Cohn, National Geographic

Koko, who had been taught nearly 1,000 words of American Sign Language by researcher Penny Patterson, added yet another skill to her repertoire when she learned how to operate an old Polaroid camera by imitating a photographer. The gorilla loved the flash of a strobe light and, after being directed to a mirror by a National Geographic editor, snapped a selfie.

When the session ended, Koko signed, "Love camera."