In 1975, photographer Nicholas Nixon took a photograph of his wife, Bebe, and her three sisters. The photograph features each of the four women — Heather, Mimi, Bebe and Laurie Brown — posed next to one another, in black and white, each staring directly into the camera. The photograph was just a whim, a momentary notion of Nixon's that captured an arresting portrait of the four Brown sisters. Afterwards, and once every year, Nixon photographed the sisters. The practice continues unabated.

Prints of Nixon's photos have been shown at galleries around the world. Beginning in November — coinciding with the publishing of a new book about the project — the Museum of Modern Art will show the collection in its entirety.

"The more you look, the more you are drawn in," Harvard Business School historian Nancy Koehn said on Boston Public Radio"You're drawn in to their faces, you're drawn in to their body language, you're drawn into how they change. (...) It is absolutely compelling as a collection of images, and — as all great art is — as a story."

Boston Public Radio cohost Margery Eagan agreed. "When I saw these pictures in the Sunday New York Times I was absolutely mesmerized," Eagan said.

WGBH Open Studio host Jared Bowen interviewed Nixon five years ago about the project. Bowen was struck by the lack of planning by both Nixon and the sisters. "They don't really talk about the project. They don't talk about why they assemble themselves in a certain way. They (...) tell no one when they're going to do a picture," Bowen said.

The details of the project seem simple, almost mundane in the telling. Koehn said that simplicity allows complex and contradictory responses from viewers.

"There's this reverberation back to the self. You notice how, in the early pictures, they're standing with some distance between them. And there are pictures where their arms are crossed. By the last five, or six, or eight photographs they're much more close, and their arms are around each other, and they're leaning on each other. You get this sense of subtle, but perceptible" closeness, Koehn said.

"Some of the years, Bebe's gaze is very penetrating. Other years she's looking at a different angle at a camera. And you're wondering, What happened in each of these lives in between the day, each year, that they took this picture?" Koehn asked.

Eagan said she saw nothing less than the steady procession of time across the photographs. "They're beautiful in their teenage years," Eagan said. "They're lovely looking, and then you see them age. (...) It was upsetting to me," not because they're aging, but "because we see so few images of older women in the media."

Nixon and the Brown sisters acknowledge that the project won't continue in perpetuity. Nixon joked about it in 2005.

Certainly my intention would be that we would go on forever no matter what. To just take three, and then two, and then one. The joke question is what happens if I go in the middle. I think we'll figure that out when the time comes.

>> To hear the entire conversation with Nancy Koehn, Margery Eagan and Jared Bowen, click the audio button at the top of the page. To see all the photographs, follow this link to the New York Times piece on the Brown sisters.