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Blame the stars.
Humanity was just beginning to recover from the realization that the Earth revolves around the Sun, and not the other way around. The Polish priest Nicolaus Copernicus (1473-1543) was a great admirer of the Persian scholar and astronomer Nasir al-Din al-Tusi (1201-1274) and the Arab astronomer and mathematician Ibn al-Shatir. , built on the observations and models of other medieval scholars. (1304-1375) took the bold step of rotating the Earth around the sun.
He knew he was hurting the self-esteem of his fellow humans. He announced in his 1543 year that he would bring the earth down from its deathbed.
But this demotion also meant that our sun was just like any other twinkling point of light. It happened to be near us, so it looked big and very bright, especially during the day.
We took relegation on the chin. We still thought the sun was at the center of the universe. This still wasn’t bad for us, even though we were trapped inside the star’s gravitational well. Riding on the blessings of the sun, we could still be important.
How a surprising discovery 100 years ago about stars of varying brightness upended humanity’s view of the known universe
This worked. However, this situation changed almost exactly 100 years ago.
amazing discovery
In October 1923, American astronomer Edwin Hubble used the 100-inch telescope at California’s Mount Wilson Observatory to detect changing brightness in the hazy cloud then known as the Andromeda Nebula. A star has been detected.
You can see this hazy Andromeda with your own eyes. In fact, the Persian astronomer Abd al-Rahman al-Sufi (903-986) wrote about this in his beautifully illustrated Book of the Stars (Kitb suwar al-kawkib al-bita), written around 964. I focused on the ambiguous parts.
A telescope later revealed that it was a cluster of stars. There were other similar ones, but they were too dark to be seen with the naked eye. But just how big were these “spiral nebulae” and how far away were they?
Harvard astronomer Harlow Shapley and many others believed that these were all part of the Milky Way, and that the Milky Way was the entire universe. Some, like Edwin Hubble, suspected that these “spiral nebulae” were “island universes” similar to the Milky Way itself. They appeared small and blurry because they were at an incredibly long distance, a distance that was unimaginable at the time.
These were two completely different perspectives on the universe. One turns out to be right and the other wrong. Science is cruel in that sense.
decisive factor
It was all thanks to one star and the incredible work of Henrietta Leavitt.
Leavitt was a “computer” at the Harvard Observatory in the early 1900s. The “Harvard Computers” were a group of skilled women who analyzed astronomical data obtained from photographic plates from various telescopes. Henrietta Leavitt studied stars whose brightness changes in a predictable way.
She identified a particular group of stars called Cepheid variable stars. She studied her 1,777 such stars. Of particular interest are the 25 stars visible from the southern hemisphere. These were part of a cluster of stars called the Small Magellanic Cloud.
Importantly, this meant that all 25 stars were located at approximately the same distance from us and their brightness relative to each other was discernible.
She discovered that these stars not only change in brightness over time, but that their brightness is related to their spacing. For example, a star whose brightness changes every 5 days will be a little dimmer than a star whose brightness changes every 12 days. This became known as the period-luminosity relationship or Leavitt’s law.
bright flame of space
This observational insight turned out to be one of the most important in astronomy. Leavitt discovered a “standard candle” that helped measure distances to distant stars.
The basics are relatively simple. Think of lighting a candle during nighttime unloading. It looks brighter when a candle is nearby. The farther away it is, the darker it will be. Since we intuitively know the brightness of the flame, we can infer the distance to the candle from its brightness.
In Cephaes, Henrietta Leavitt spots a candle in the night sky. If we can measure the brightness cycle of a Cepheid star, we can tell how bright it should be. If it appears darker in the sky, it means it is further away.
We also know that when the distance doubles, the light goes out four times. If the distance triples, the light goes out nine times (for science geeks, this is called the inverse square law). Importantly, this allows astronomers to calculate the distance to the star.
Cepheid variables could then resolve the debate over the nature of spiral nebulae.
Almost 100 years ago, in October 1923, Edwin Hubble discovered the first Cepheid star in the constellation Andromeda. The repetition of brightening and dimming revealed that this Cepheid was quite far away from the Milky Way.
Therefore, Andromeda was a galaxy like ours. Because it is far away, it only appears faintly small. Today we know that it is more than 2 million light years away from her.
Hubble fundamentally changed the way we view the universe. We were just recovering from the Earth’s demotion as the center of the universe. Now, it turns out that the universe is also unimaginably large.
When news of Edwin Hubble’s new distance estimate to Andromeda reached Harlow Shapley, he famously commented, “It destroyed my universe,” and that the universe is not necessarily something we cherish. I emphasized the fact that I don’t care what you think.
Henrietta Leavitt definitely deserves the Nobel Prize for achieving one of the most important discoveries in astronomy. Edwin Hubble nominated her for this award in 1925. Unfortunately, she already passed away in 1921 at the relatively young age of 53, and this award will not be awarded posthumously.
Today, we know that there are more than 100 billion galaxies in the known universe. But so what? The Milky Way is still our galaxy, and we must still be at its center.
But instead, some of the responsibility must be placed on Harlow Shapley.
our place in the universe
Like any good scientist, Shapley continued to pick up the pieces of the destroyed universe and use Cepheids (and other types of variable stars) to determine the shape of the Milky Way and our place within it. Ta.
He discovered that the solar system was not at the center of the Milky Way galaxy, but instead was floating on the outskirts of the galaxy.
Today, we know that our Sun is part of an inconspicuous spiral arm located about 30,000 light-years from the center of the Milky Way galaxy.
We still can’t step outside the Milky Way to take selfies. But we look at the spiral arms of the Andromeda galaxy and imagine that there are stars like our sun, planets orbiting there, and perhaps life forms thinking about their place in the universe. can.
In close-up, only noise is visible. That is, the dots are spread throughout the image. But here each dot is a star. Although we cannot see it, we expect planetary worlds to orbit around each of these points. And within those worlds, there may even be species that can understand their own insignificance in this vast universe.
Homo sapiens, living on a rocky world on the outskirts of the Milky Way, are beginning to understand the vastness of the universe. For this, they have a brilliant woman who discovered a type of star that changes in brightness and how to use this change to measure distances to distant galaxies.
Long live Homo sapiens, long live curiosity!
The author is a professor of integrated sciences and humanities at Hampshire University in the United States. He is also an astronomer affiliated with the Five College Astronomy Department in Massachusetts and hosts his Urdu YouTube channel ‘Kainaat Astronomy’.
EOS, published at dawn on March 31, 2024
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