In the early 1900s, the universe appeared to be a a lot, a lot smaller place. Again then, astronomers believed the Milky Approach galaxy was all there was. They didn’t know there have been billions of different galaxies; they didn’t know the way small we actually are.
They didn’t know this as a result of they couldn’t measure distances to far-flung stars. Why? There was a fairly easy drawback in astronomy: A brilliant, faraway star seems nearly the identical as a dim star that’s shut by.
It’s the identical right here on Earth. Think about you’re on the seaside at night time and see two lighthouse lights glowing in the distance, however one appears brighter than the different. For those who knew each lighthouses used the identical lightbulb, you can conclude that the dimmer gentle is farther away. However it’s additionally attainable that the dimmer gentle simply comes from a lower-wattage lightbulb, maybe nearer to you.
Scientists wanted a manner to discover out the intrinsic brightness of stars — to work out their wattage, so to converse. That’s when Henrietta Leavitt, a Massachusetts-born “laptop” who labored at the Harvard Faculty Observatory, got here alongside. In 1908, she printed a discovery that will sound small however is considered one of the most necessary in the historical past of astronomy. As we talk about on this week’s Unexplainable podcast (see the embed above), it cracked open the universe.
Blinking lights present a yardstick to measure the universe
Earlier than Henrietta Leavitt, many astronomers checked out the stars in what’s right this moment often called the Andromeda galaxy — some 2.5 million light-years away — and mistakenly thought they have been a part of our personal Milky Approach galaxy (which is solely round 100,000 light-years in diameter).
These Andromeda stars have been orders of magnitude additional away. Scientists simply didn’t realize it.
At the time, astronomers had some strategies to work out distances to stars, however they solely labored for stars comparatively shut to Earth. Leavitt’s discovery — linking the pulse of 1 sort of star to their precise brightness, as described in the graphic above — was the key to measuring objects farther and farther out into area.
If astronomers needed to measure faraway issues, Leavitt’s discovery confirmed, they simply had to look out for cepheids. Her method led astronomers to chart out relative distances to stars: They might use it to examine two stars and work out which one was nearer.
It took some extra work by different scientists to calibrate this yardstick, to put concrete numbers on it. However as soon as they did, and began measuring with it, the cosmos grew and grew.
Leavitt paved the manner for Edwin Hubble to uncover galaxies past our personal
Fifteen years after Henrietta Leavitt’s discovery, the preeminent astronomers Harlow Shapley and Heber Curtis have been locked in a heated debate.
Curtis believed that Andromeda was a separate galaxy far, distant from the Milky Approach. At the time, this was an outlandish concept. Shapley represented the extra mainstream view — that Andromeda was simply a hazy, cloudy area inside our galaxy, which he had just lately estimated to be round 300,000 light-years throughout. That was additionally the assumed measurement of the whole universe.
If Curtis was proper, it might imply the universe was double or triple the measurement that Shapley estimated — no less than.
To settle the debate, Edwin Hubble — the namesake of the well-known area telescope — regarded for Cepheid stars in Andromeda. Evening after night time, he took images of Andromeda, looking for cepheids. In October 1923, he discovered one, blinking in considered one of Andromeda’s spiral arms. One other week of observations allowed him to comply with Leavitt’s method and decide its distance.
Hubble estimated it to be round a million light-years from Earth — effectively exterior the boundaries of Shapley’s universe. (Hubble was a little off: Andromeda is nearer to 2.5 million light-years away.) After studying about Hubble’s discovering, Shapley reportedly mentioned: “Right here is the letter that destroyed my universe.”
This is a image of the cepheid star Hubble noticed in Andromeda, referred to as “variable primary” — or V1 — captured by Hubble’s namesake telescope in 2011. V1 has been referred to as “the most necessary star in the historical past of cosmology.”
NASA, ESA, and the Hubble Heritage Staff
Scientists stored constructing on Leavitt’s ruler to measure the universe. And as they used these measuring instruments, their understanding of the universe advanced. They realized it was far bigger than beforehand thought, there are billions of galaxies, and it’s increasing: These galaxies are shifting additional and additional away from each other.
Astronomers additionally realized that the universe had a starting. If galaxies are shifting away from each other now, it means they have been nearer collectively in the previous — which led scientists to the concept of the Big Bang.
It additionally led them to understand that the universe could, ultimately, finish.
This week’s episode of Unexplainable, Vox’s podcast about unanswered questions in science, tells that story and extra.