Shulou(Shulou.com)11/24 Report--

Let's start with a story.

In 1920, the U.S. government conducted a census in Cambridgeshire, Massachusetts. A census taker walks into a poorer community and goes door to door to investigate how many people live here and what they do.

He knocked on the door of a family in the community and saw a mother and daughter who depended on each other. The daughter, a deaf girl, went to a lot of trouble to figure out why the census taker was here. When asked about her career, her answer was "scientist".

The census taker laughed at that time. In the United States at the beginning of the 20th century, scientists were the exclusive domain of men, and few women could get a doctorate. So he couldn't believe that a deaf girl living in a poor community could become a scientist.

Henrietta Lewitt. Her name is Henri Aitavit, the mother of modern cosmology. She is the only person in history who can be called the mother of a major discipline.

In 1868, Levitt was born into a pastoral family in Massachusetts. At the age of 20, she passed a rigorous exam and was admitted to Radcliffe Women's College, one of the famous seven sister colleges that was later merged by Harvard University. In 1892, Levitt graduated successfully and received his bachelor's degree. Then, in accordance with the tradition at that time, she went to Europe by boat and began her graduation trip.

But something happened in the sky. During the trip, a sudden illness damaged her eyesight and hearing. Although her eyesight later improved, her hearing went from bad to worse until she finally lost her hearing. For nearly 30 years since then, she has been in a state of illness.

After returning from the trip, Levitt decided to pursue a master's degree in astronomy. She joined the Harvard Observatory run by Edward Pickering in 1893 and became a "Harvard calculator".

Levitt became a "Harvard calculator" but unfortunately, her health was a serious drag on her studies. Because of her sickness, Levitt has to call in sick every now and then, which makes her scientific research work fragmented. Of course, this also made her mentor Pickering quite unhappy.

In 1896, Levitt realized that she could no longer complete her studies. In desperation, she gave up and left the Harvard Observatory for six years.

Six years later, in 1902, Levitt wrote a letter to Pickering. In the letter, Levitt mentioned that she was no longer qualified for other jobs because of her hearing impairment, so she wanted to apply to return to the Harvard Observatory. Pickering agreed. But this time, Pickering learned wisely and did not let Levitt participate in the observatory's most important star classification work, but sent her to study the Cepheid variables alone.

At the beginning of the 20th century, humans could not even figure out the simplest kinds of stars in the sky, let alone the extraordinarily complex problem of variable stars. In this case, sending a person to study the Cepheid variable alone is tantamount to exile in the frontier.

Let's pause this movie about Levitt and feel her situation when she returns to the Harvard Observatory. Suffering from illness and deafness, he was forced to return to the sad place where he gave up his master's degree, and then was assigned to a scientific wasteland that no one had set foot on before. I'm afraid few people can get out of such a desperate situation.

But this is our last encounter with an ordinary woman, Henri Love Tahlewitt. What happened after that was as legendary as Moses' separation of the Red Sea with a walking stick.

Since 1904, Levitt has been finding new Cepheid variables in the Magellanic Cloud at an astonishing rate. She looked so fast that an astronomer wrote to Pickering: "Miss Levitt is a master at finding variable stars." we didn't even have time to record her new findings. "

In 1908, Levitt published a paper in the Yearbook of the Harvard Observatory, announcing that he had found a total of 1777 Cepheid variables in the Magellanic Cloud. This astonishing number immediately caused a sensation in the astronomical community, and even got a report from the famous Washington Post.

Magellan Cloud but this sensational discovery of Cepheid variables is nothing compared to the most valuable part of this paper.

At the end of the paper, Levitt selected 16 Cepheid variables in the small Magellanic Cloud and listed their light cycles (the time it takes to complete a round of light and dark alternation) and apparent magnitude in a table. She left a comment on the table: "this is noteworthy. The brighter the star, the longer the period of light change."

Four years later, in 1912, Levitt perfected this conclusion. She selected 25 Cepheid variables in the small Magellanic Cloud and drew them on a picture with the brightness as the X axis and the light cycle as the Y axis. As a result, the 25 Cepheid variables happen to be arranged in a straight line. According to this, Levitt asserts that "the brightness of the Cepheid variable star is proportional to its light change period."

In order to understand the weight of this seemingly mundane sentence in the history of astronomy, you can imagine a wasteland that has been frozen for many years. Because of this magical spell, hundreds of millions of beautiful flowers bloom in the blink of an eye.

This sentence was later called Leavitt's law. It is this earth-shaking Leavitt's law that opens the door to modern cosmology.

You may feel a little confused: "Why can such a simple law create a whole new discipline?" The answer is that it provides a whole new method of distance measurement, which is the famous standard candlelight.

In order to introduce the basic principle of measuring distance by standard candlelight, let's start with a phenomenon that is quite common in daily life. A candle is bright when it is near, and dark when it is seen from a distance. This is because the brightness of the candle we see depends on the number of photons emitted by the candle and shot into our eyes. The more photons emitted, the brighter the candle looks; conversely, the darker the candle looks.

The schematic diagram of measuring distance with standard candlelight is shown in the figure. The total number of photons emitted by a candle whose absolute brightness remains the same remains the same. These photons will spread outward in a sphere. So somewhere, the number of photons received per unit area is inversely proportional to the square of the distance from the candle here. This means that the apparent brightness of the candle we see somewhere is inversely proportional to the square of the distance from the candle here. For example, if the distance is increased by four times, the apparent brightness of the candle will be reduced to the original 1max 16.

In this way, we can use candles to measure distance: first, put a candle in a place close to it, and measure its distance and apparent brightness. Then, place another candle with the same absolute brightness at a distance and measure its apparent brightness. Finally, using the inverse relationship between the apparent brightness and the square of the distance, the very long distance can be calculated.

Measure the universe with candles the principle of measuring distance with candles is also applicable in heaven. To this end, it is necessary to find a special celestial body in the sky, which can meet the following two conditions at the same time:

①, it is so bright that it can be seen even at a great distance.

② has stable optical properties and fixed absolute brightness. If we can find such a celestial body, we can use it as a candle to measure the distance on a cosmological scale. This special celestial body that can be used as a candle is the so-called standard candlelight.

Now that we know the concept of standard candlelight, we can talk about the meaning of Lewitt's law. Since the Cepheid variables selected by Levitt are all located in the small Magellanic clouds, they can be approximately considered to be equidistant from Earth. Therefore, as long as their apparent brightness is equal, their absolute brightness must be equal.

Levitt's law states that the absolute brightness of a Cepheid variable is proportional to its light period. This means that as long as you choose a Cepheid variable with exactly the same light period, you can get a number of celestial bodies with exactly the same brightness.

So Levitt's law means that the Cepheid variable satisfies the two conditions of standard candlelight, which is a kind of standard candlelight in the real sense. This is also the first standard candlelight found in human history.

The discovery of standard candlelight provides a new way to measure distant cosmological distances. You may still wonder: "Why can the discovery of a new method of distance measurement create a whole new discipline of modern cosmology?" In fact, it was this discovery that shook Copernicus's heliocentric theory.

Let's say a few more words about Leavitt. Sadly, Leavitt's story did not have a happy ending.

Shortly after discovering that the Cepheid variable was a standard candlelight, Levitt resigned again because of stomach surgery. By the time she came back, Pickering had given her a new job: measuring the North Star sequence, analyzing the spectra of 96 stars near the North Star. This is the project that Pickering has loved and wanted to accomplish for many years.

It is only reasonable for a manager to send his most capable staff to deal with the challenges he finds most difficult. But for a level of astronomer like Leavitt, the arrangement is absurd, forcing Michael Jordan to give up his basketball career to play in an unclassy baseball league. To make matters worse, Levitt had no choice at all under the eaves. Since then, she has never been able to return to standard candlelight research.

Pickering's selfish decision also set back the study of variable stars around the world for decades.

Ironically, although he started a whole new discipline that later supported thousands of doctorates on his own, Levitt himself failed to get a doctorate. Many years later, she is still a Harvard calculator whose salary is half that of a man.

In 1921, Levitt, who had always depended on his mother, fell ill again. This time it's an incurable cancer. On December 12 of that year, she left on a rainy night. In her will, she left all her property to her mother. The total value of the inheritance is $315, which is only enough to buy eight carpets.

After his death, Levitt was buried in his family's graveyard. She could not even have her own tombstone and was forced to huddle with more than a dozen relatives. The tombstone is small enough to write down her name, birthday and date of death.

The Tomb of Lewitt this is the final end of the discoverer of standard candlelight, the Copernican heliocentric gravedigger, the mother of modern cosmology, and a great female scientist.

More than 100 years have passed, and now the name Henrietta Levitt is almost forgotten in the dust of history. But I still want to write an article to commemorate the sufferings and honors experienced by this extraordinary woman. In spite of illness, deafness, poverty, loneliness, being manipulated, despised and forgotten, she is still the eternal candle that illuminates the whole universe.

Wen Yuan: "telling teenagers about Cosmic Science" by: Wang Shuang, Editor: Zhang Runxin, this article comes from the official account of Wechat: Origin Reading (ID:tupydread), author: Wang Shuang

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