The universe appeared to be much, much smaller in the early 1900s. Astronomers at the time thought the Milky Way galaxy to be all that existed. They were unaware of the billions of other galaxies in the universe and how little our galaxy actually is.
They were unaware of this since they were unable to gauge the distances to distant stars. Why? There was a really straightforward issue in astronomy: A bright star in the distance appears to be almost identical to a dull star nearby.
The same holds true for Earth. Imagine being on the beach at night and spotting two lighthouses in the distance, but only one of them appears to be as brilliant as the other. You may infer that the lighter light is farther away if you knew that both lighthouses utilised the same lightbulb. However, it’s also possible that the softer light is simply the result of a nearby, lower-wattage lightbulb.
The intrinsic brightness of stars, or their so-called wattage, needs to be determined by scientists. At that point, Henrietta Leavitt, a “computer” from Massachusetts who worked at the Harvard College Observatory, appeared. She produced a discovery in 1908 that, despite its seeming smallness, is among the most significant in astronomical history. It cracked open the world, as we explore on this week’s Unexplainable episode (see the embed above).
Flashing lights serve as a yardstick for measuring the cosmos.
Many astronomers before Henrietta Leavitt mistook the stars in what is now known as the Andromeda galaxy, about 2.5 million light-years away, for being a component of our own Milky Way galaxy (which is only around 100,000 light-years in diameter).
Those Andromeda stars were a great distance distant. Scientists simply weren’t aware of it.
Astronomers at the time had some methods for calculating star distances, but these only worked for stars that were quite close to Earth. The discovery made by Leavitt, which relates a particular type of star’s pulse to its real brightness as seen in the illustration above, was crucial for measuring things that were placed farther and farther into space.
Leavitt’s finding demonstrated that all astronomers needed to do to measure distant objects was keep an eye out for cepheids. Astronomers used her technique to map out the relative distances of stars, allowing them to compare two stars and determine which was closest.
It took more research on the part of other scientists to calibrate this yardstick and assign it numerical values. But as soon as they did and began using it for measurement, the universe continued to expand.
Leavitt made it possible for Edwin Hubble to find galaxies outside of our own.
Harlow Shapley and Heber Curtis, two of the world’s greatest astronomers, were engaged in a contentious argument fifteen years after Henrietta Leavitt’s discovery.
Curtis thought that Andromeda was a distinct galaxy that was incredibly far from the Milky Way. This seemed ludicrous at the time. Shapley stood for the more common perspective, which held that Andromeda was merely a hazy, cloudy region within our galaxy, which he had recently calculated to be roughly 300,000 light-years large. The size of the entire cosmos was also supposed to be that.
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If Curtis was correct, the cosmos was at least twice as large as what Shapley predicted.
The famed space telescope’s namesake, Edwin Hubble, searched Andromeda for Cepheid stars to settle the argument. He photographed Andromeda night after night while looking for cepheids. He discovered one, blinking in one of Andromeda’s spiral arms, in October 1923. He was able to use Leavitt’s formula and calculate its distance after making further observations for a second week.
Hubble calculated its distance from Earth to be roughly a million light-years, placing it considerably outside Shapley’s cosmos. Since Andromeda is actually closer to 2.5 million light-years away, Hubble was somewhat off. Shapley reportedly stated, “Here is the letter that wrecked my cosmos,” after learning about Hubble’s discovery.
This image of the “variable number one” (or V1), a cepheid star Hubble detected in Andromeda, was taken in 2011 by the Hubble-named telescope. The term “most significant star in cosmological history” has been used to describe V1. Leavitt’s ruler was expanded upon by scientists from NASA, ESA, and the Hubble Heritage Team. Their knowledge of the universe also advanced as a result of their usage of these measuring devices. They discovered it to be much larger than previously believed, with billions of galaxies, and that it is growing, since those galaxies are getting farther apart from one another.
Additionally, astronomers understood that the universe had a beginning. Galaxies were closer together in the past if they were drifting apart presently, which led scientists to theorise about the Big Bang.
