A 350-foot tiger peered out from the south side of the Empire State Building on Aug. 1, its large paw draped across dozens of windows.

It was joined by a snow leopard, a breaching whale, and even various insects. These massive creatures lit up the side of New York City’s famed skyscraper in a collaboration between artist Travis Threlkel and Boulder-based director Louis Psihoyos, which used 40 projectors to spotlight pictures of endangered animals by three photographers, including National Geographic photographer Joel Sartore.

Sartore founded the Photo Ark, a 20-year project to document and catalogue the world’s 12,000 captive animal species, as well as to show people the beauty that extinction threatens. Though seemingly unrelated, the genesis for this beloved project came from Sartore’s own family.

In 2005, Sartore’s wife Kathy was diagnosed with advanced breast cancer. While he stayed home to care for her and their three children—instead of rushing to shoots around the world—he began taking photographs of animals at the local zoo, and the project grew from there. In 2012, Kathy had a recurrence and their son was diagnosed with stage-three lymphoma. Though both are now cancer-free, the family’s encounter with cancer changed the way Sartore approaches his life and the messages he communicates. He’ll be the keynote speaker this Saturday at the University of Colorado Cancer Center’s annual Dinner in White fundraiser, where he will share his photos and stories of his family’s personal battle with the disease. Here, we talk to Sartore about his family, the Photo Ark, and what he’s learned from both.

5280: What made you decide to make this photo series of your family?

Joel Sartore: I’m a contributor to the CBS Sunday Morning show with Charles Osgood, and cancer was such a major portion of our lives that I decided to do a piece on what it’s like to live with cancer when my wife got sick, and then I did a second one when my son got sick and talked about the process of healing, and what it means to go through it. In most cases, it’s cathartic for me to be able to tell the story, with my wife and son’s permission, of course. It’s very cathartic for me to be able to talk about it with somebody, and I hope other people know that they’re not alone, that lots of people go through this, and there’s light at the end of the tunnel. It’s really important to make those connections, I think.

How did you approach your family about it?

Well, the first thing to understand is that I didn’t work this like a National Geographic assignment. I didn’t shoot very many pictures of them when they were sick and bald and all that. I just asked their permission to take a picture now and then, sometimes just with smartphone, and mainly to write about it. They were fine with it because they’ve had stories told about themselves as long as I’ve known any of them, because I’m a journalist, and I often write about them and photograph them, my entire family, not just the ones who get sick. They are very tolerant and patient with me and basically put up with me, so for that I’m grateful.

How is it different to be photographing family members versus being out on assignment for National Geographic or another publication?

I think it’s easier to photograph your own family in a way because they’re right there, they love you, they tolerate you, you have 24-hour-a-day access to them. Anybody who has family understands that, because of the unprecedented access you get to your family, you should be able to tell their stories very, very well. To me, it’s easier than being on a National Geographic assignment, and certainly if I had to go to a complete stranger and ask if I could document a life-threatening illness they had. Much easier.

What is the most powerful story or photograph that you’ll be sharing during your talk?

I just think that the entire message is kind of the point. It’s not a single story, but it’s the fact that life is very short. As my wife put it once she was declared out of the woods, she said, ‘You know, the only bad thing is that I’m still going to die from something, even though I beat this.’ And that’s true. We all do leave this earth in the end, so ultimately whether you have cancer or not, the thing to keep in mind is you’ve got to make every single day count. You’ve got to do good while you’re here on the planet, and that’s what the talk is really about. It’s concentrating on doing good things and making your life count every day, not to waste a single day. There’s no reason for it.

Is this a lesson you apply to your work now with the Photo Ark and other assignments that you do?

That’s exactly right. The Photo Ark was born because my wife got sick. I was forced to stay home for a year and take care of our kids, and on the days when she felt good—through her chemo there were times when she felt good—I just went to my local zoo, the Lincoln Children’s Zoo [in Nebraska], and started to take pictures there. I did them studio style, with studio lighting and black-and-white backgrounds, and that’s literally how the Photo Ark was born, because I wanted to do good with my time. I figured my career was half over. I wanted to do something that lasted and that would serve not only humanity but nature. One of the things I’m going to talk about is the Photo Ark and the fact that if it weren’t for Kathy getting sick, the Photo Ark would have never happened. There seems to be a silver lining in every cloud.

How did you feel seeing your photographs on the Empire State Building, and what kind of impact do you think having those photos so public will be?

What I hope is that beyond just seeing my pictures up there on the side of the Empire State Building, I hope the public catches on to the fact that nature is amazing, and we have to make sure that we save the other species we share the planet with. If we don’t, we’re in big trouble. I mean huge trouble. Humanity cannot survive an extinction that we’re talking about coming. Half of all species by the turn of the next century could be gone. The point of this is to get the public to care about the extinction crisis and be moved to action while there’s still time to turn this around, while there’s still time to save species.

What do you think it is about a photograph’s distinct moment in time that makes it so powerful?

I think the human mind likes still photographs. The human mind likes to be able to stop and study something. Still photographs have a tendency, if they’re good, to go beyond the original situation and become iconic. That’s something I always seek to do. I don’t always achieve that, but if I can make an animal iconic, that’s really a good thing. For many species, this is the only chance they’ll ever have to have their voice heard on an international level, to really be noticed around the world. This is their chance. When we save other species, we’re saving ourselves. We have to realize that, as nature falls apart, so do we. I’m very hopeful that something like the Photo Ark could help start a trend to get people to care. It’s all because of the power of still photography and how well that works with the human mind.

To learn more about Dinner in White or how you can attend on Saturday, visit the event’s website. To learn more about the Photo Ark, visit the website or follow Joel Sartore on Instagram, @joelsartore.

(Read more from our “15 Minutes With…” series)