As the year began to come to a close, we asked National Geographic staff who work closely with photography—through the magazine, Your Shot, News, Travel, and Proof—to choose a photo from 2015 that they just can’t stop thinking about. There’s no formula for what makes an image resonate—it can be a piercing gaze, the perfect light, or a tender moment that strikes a chord with our editors. Over the coming days, we’ll reveal the 2015 photographs they found most memorable and why.

It was a very tough this year to choose just one image, as we had so much strong work to choose from, like the powerful images by Peter Muller for our Ebola story, Robert