Authors, like books, should not be judged by their covers. Consider Joan Didion. At nearly 77, with bones like toothpicks and a spectral face hidden behind large-framed glasses, she looks fragile. She is anything but.

Although she made a name for herself decades ago by writing cool, frank commentaries about the cultural movements in 1960s California, she is more recently known for her personal losses. In December 2003, her husband of nearly 40 years, fellow writer John Gregory Dunne, died of a heart attack while she was fixing him a salad. Didion wrote about his death in “The Year of Magical Thinking” (Knopf, 2005), which was nominated for the Pulitzer Prize for biography or autobiography.

But just weeks before the book was published, the daughter she and Dunne had adopted, Quintana Roo, died of acute pancreatitis. Quintana was 39 years old.

Didion survived the only way she knew how: She wrote an­other book. “Blue Nights” ($25, Knopf), named for the lingering dusk hours of the summer solstice, was released Nov. 1. Labeled a memoir, it is a raw exposé of Didion as a mother and a confession of her reluctance to face what lies ahead: old age.

Didion spoke with us by phone from her apartment in New York; during our conversation she alluded to possibly addressing aging in her next project. Although she declined to give details, it’s safer to bet on Didion’s strength than on her weakness.

Why do you write about your pain? Isn’t that like pouring salt on the wounds?

Writing is what I do. Writers tend to think of writing things down as opposed to not writing them down. I wouldn’t use the word “therapeutic” because there is actually no therapy for this. On the other hand, if something is looking me right in the face, I have to look back at it.

You wrote that you felt “outraged” when Quintana Roo was in the hospital because “this was not supposed to happen” to her, or to you. Are we ever prepared for tragedy?

No, I don’t think we are. I certainly wasn’t. Nothing could have surprised me more than that series of events. But when I look back, I was terribly surprised that John died, and there was no reason to be, because he had heart trouble. I had simply ignored this and pretended like it wasn’t going to happen, and certainly wasn’t going to happen to me.

Do you think John’s death prepared you for Quintana’s?

I think it prepared me not to have high expectations.

You don’t write much about what you did aside from work after John and Quintana died. Have you leaned on anyone?

I had some friends who were really great during that period — great in that they let me express what I thought was really going on. When Quintana was sick and I’d have dinner with a friend, it was the people who let me say, “I think she’s dying,” that I really appreciated. Some people don’t let you say that. Some people think it is disloyal of them to allow you to be that honest.

You describe Quintana as wise beyond her years. Yet you give the impression that you were not aware of these elements of her personality until much later.

That was another reason that I actually felt a need to write the book. I felt a need to acknowledge the things that I hadn’t noticed or acknowledged when she was small, when I had treated her like she was a charming but not quite bright baby. And she was actually always thinking.

Late in Quintana’s life, I told her I sometimes thought I wasn’t such a great mother. And she said, “No, you were okay, you were a little remote.” Well, that was probably true. That remoteness is deep in my personality. It was never a remoteness to Quintana specifically. John was not remote. He was always right there, up in front.

You’re known for maintaining a distance from your subjects when you write, and this distance seems to have bled into real life.

Absolutely. I think that’s why, with this book in particular, I wanted to be more direct. I wanted to turn outward a little or, rather, to let people in.

“The Year of Magical Thinking” concluded with a sense of finality. “Blue Nights” is less resolved. Did you feel any relief after this book?

No, but what I felt was that I had expressed myself. I had put down what had happened and what it meant to me. And what I discovered in the course of doing so was that there was no resolution, no ending, no huge finale. There is no starting over.

After the length of time that’s passed, I think I’ve finally processed the fact that John has died. With Quintana, though, I really just began facing that with this book. It opened me up in a way. And it’s an entirely different process this time, because I never felt responsible when John died. I know perfectly well that it’s not logical to feel responsible for Quintana dying, but I still do. She was my baby; she was a person who was given to me to take care of.

How do you feel about confronting old age?

It’s a subject that has, until recently, completely escaped me. I simply hadn’t considered it. It was something that was going to happen to someone else, kind of like dying itself. This has been a theme in my life. Actually, I can’t talk too much about it because I’m trying to write about it. . . . But it’s on my mind, certainly.

Are you ready to be old?

I’m not ready. I’m still not ready. Every once in a while, though — maybe because since [I started “Blue Nights”] I’ve been confronting it — I will have a thought late at night that says, “I’ve got it down now, I am getting older, I am going to continue getting older, and it’s going to be fine.” But then it slips into the nowhere land again.

What makes you happy these days?

I’ve found there are a lot of things you don’t count on to make you happy, that do. Last night I was on my way home from Philadelphia and there was a sunset. Now, it sounds silly, but seeing this sunset over New Jersey actually made me happy. And that’s not a famous sunset.