"The starry sky above me, the moral law within me” Kant said, and continues to say it today from the epitaph on his tomb which reads as follows.
Henrietta Swann Leavitt not only did he subscribe to these words, but he contributed like few others to giving them meaning. In fact, it is thanks to her that we have developed a broad and in-depth approach knowledge of the starry sky above us, which was still substantially unknown in Kant's time.
Henrietta prepared the theoretical and practical instrumentation that allowed us to move from a 'provincial' understanding of the universe to the one we have now.
From a static universe made up of a single galaxy to a universe made up of billions of galaxies and in rapid and progressive expansion.
How to say from Ptolemy to Copernicus, more or less.
THE HARVARD ASTRONOMICAL OBSERVATORY
The daughter of a Congregational church minister descended from early English Puritan settlers, Henrietta was born in 1867 and graduated from Radcliffe Women's College at 23. She then joined as a volunteer human computer team ofHarvard astronomical observatory directed by Edward Pickering.
Pickering he had embarked on the task of precisely mapping all the stars of our galaxy, which at the time was considered exhaustive of the entire universe. The mapping included describing the stars in terms of brightness, color and distance from the earth.
This type of activity required a considerable amount of precision and great computing power which, since silicon computers did not exist, was provided by women who had studied and were able to perform the required calculations at little cost (they were paid about 25 cents an hour).
In particular they calculated the distance of the stars with the method of parallax, which essentially consists in making two observations of the same object from two points of view as distant as possible, and in obtaining - with the trigonometry – from the distance of the two observation points and from the angle of movement of the object (the parallax, in fact) the distance between the observer and the object.
Too bad that the parallax method only works for relatively nearby stars, no further than a few hundred light years from us.
The more the distance increases, the more, as is intuitive, the parallax angle decreases, and therefore the measurement of the distance becomes more imprecise, to the point of becoming substantially impossible.
LEAWITT UNDERSTANDS HOW TO MEASURE THE UNIVERSE
And here it comes Henrietta, who had been entrusted with the task of identifying and measuring variable stars Cepheids in what was called the Small Magellanic Nebula.
Cepheids are stars whose brightness varies at rather regular intervals for each individual star.
The method consisted of superimposing the negative photographic image of a star with its positive image and thereby detecting any differences, indicators of the variability.
Different images taken at different times also gave the measurement of period (with what rhythm they pulsate).
Leawitt soon notices that there is a precise connection between the rate (period) of variation and brightness: the greater the brightness, the longer the times between one contraction and another.
It follows that two stars with the same period have the same intrinsic (i.e. real) luminosity, and if they do not appear like this to us it is because they are at different distances.
A four times greater luminosity between two stars of the same period, for example, indicates that the less luminous one is twice as far away (since the light decreases in intensity as the inverse square of the distance).
At this point it was enough to know the distance of a Cepheid variable star to know the distance of all the others and of the luminous bodies close to them, therefore ultimately measuring the universe.
Result that was obtained with the method of parallax using the motion of the sun around the center of the galaxy: once the distance of one variable was known, it was then easy to derive that of the others with the principle enunciated by Henrietta.
Then using the standard spark plugs (the Cepheid variable stars) discovered by Leawitt it was quickly understood that the nebulae were other galaxies outside our own and that the universe was immeasurably larger and richer than previously thought.
It is precisely thanks to the discoveries of Leavitt is Hubble (as he himself repeatedly acknowledged) he came to realize that galaxies move away at an incremental rate depending on their distance.
in short a new Copernican revolution, a true paradigm shift.
A SHORT LIFE DEDICATED TO ASTRONOMY
Henrietta died in 1921 at the age of fifty-three from stomach cancer, after a reserved life entirely dedicated to astronomy and unfortunately marred by various illnesses, including complete deafness which struck her while still young.
She was never heard to complain, she was always well disposed and cheerful.
In 1925 the Stockholm Academy took an interest in her to award her the prize Nobel, only to discover that she had already passed away: and by regulation the prize cannot be awarded posthumously.
They bear his name lunar crater and a asteroid.
We thank PAOLO RICCARDO FELICIOLI for his contribution