Elena Poniatowska: The great popularizer of Mexican astronomy

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Slim, alert, charming, Julieta Fierro ran across the stage, her voice sharpened by a trail of stars. From a shopping bag (one of those now made of plastic, once jute) she pulled the essential elements for her lecture: an orange, a grapefruit, a banana, and several hawthorns, and so I thought I'd learn something about astronomy, even if I was just a knowledgeable legal expert. Her name resonated throughout the Institute of Astronomy at the National Autonomous University of Mexico, but I know that the observatory in Tonantzintla loved her because she was so lovable. The doctors in astronomy listened to her smiling. Julieta Fierro appeared from time to time in Tonantzintla, and later she also traveled to the observatory in Baja California. I always saw her as a shooting star, and I always listened to her, wanting to hold her in my arms.

Julieta Fierro gave her lecture completely free of embarrassment, dazzling us with various accessories she pulled from a grocery bag. The Sun was a grapefruit. It filled the night sky of our minds with information of almost musical joy and made certain truths and beliefs available to us as if they were recipes. "Although comets pass very quickly across the sky, they are fried over a slow fire," she explained. Without intending to, she was gifting us with accessible knowledge of the Holy Lord Night Sky, deserving of all respect. I could retain and digest what Julieta said and turn it into a flan of eggs, milk, and caramel ready to crown some constellation.

"Look," he told us, "the closest star to Earth is the Sun. It's the only one whose diameter we can easily measure, as well as learn many of its properties. The Sun, at this scale" (Julieta took out a ping-pong ball), "would be a little ball about this size, and about a million Earths would fit inside it. So you can really get a sense of its magnitude. Look closely at this grapefruit. The Sun is a pretty average star, and our planet is very small. Very few blue giant stars are born, and many stars called "white dwarfs" pass through the night sky, but they all spend most of their lives the same as they were born; they don't change, they don't grow. It's as if nature prefers to make small objects rather than large ones; there are many white and red dwarf stars."

–But does red have to do with size?

–With the temperature.

–Does temperature have anything to do with age?

–When they are born, no.

–First they are red and then they turn blue?

–No, no, almost all blue stars are giants. Dwarfs are red.

–And how can you know its size?

–It can be measured. The diameter of stars can be measured with eclipses. Now, yes, indeed, there is evolution of stars, and it depends on how much matter they have. On the one hand, all stars are born in a certain way and live most of their life without changing. Those that grow red are almost always red dwarfs. But all stars are born within gas clouds, whether small, medium, or large. The gas and dust are scattered or dispersed among the stars. Orion, for example, can be seen with the naked eye. This is a photograph that shows exactly where stars are born. When there is dust, the cloud contracts, and the star is born in the center.

–Why can’t we see her?

–Because its evolution takes 10,000 years and because it's surrounded by this cocoon of matter that prevents us from seeing its interior. Look at the night sky and you'll see the place where a star has just been born, complete with its halo. If I spin any object, you'll see it has a square shape; so, when there's a cloud of interstellar matter that contracts to become a sphere, if it's spinning, it begins to contract and flatten out; that's when a cloud contracts to give birth to a star. Almost all the matter goes to the center of the cloud, and the star is born. The excess matter continues to spin around it and forms a disk.

–Are there stellar winds?

–Yes, because stars, when they're born, are extremely active and produce not only a lot of light, but also very powerful stellar winds. A star is a sphere of incandescent gas that throws light into space. If the star produces a wind, it will push everything nearby, and it will produce a jet perpendicular to the disk. That's exactly what happens in the places where a star is born. Here, there would be a disk of matter rotating around the newborn star, with its wind of light emerging from one or both sides of this newly formed disk. Precisely, here we have the disk of a newborn star, and only the gas and light can emerge perpendicular to the disk, and the objects around it can be observed, like this little cloud that illuminates the Herbing-Haro objects in these disks…

I listened to Julieta without understanding her, but I felt like I was flying in the night sky, and I hoped the wind of the stars would carry away my ignorance. I loved Julieta talking about the places where stars form, but I couldn't see them, even though she knew everything. I hope that one night the star Julieta Fierro will appear and guide me through stellar space, just as I do in the many lectures I will miss on the darkest nights.