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This article was originally shown on The conversation.
A hundred years ago, astronomer Edwin Hubble The size of the well -known universe is dramatically expanded. During a meeting of the American Astronomical Society in January 1925, a paper of one of his colleagues reported on his behalf that the Andromeda Nebula, also known as M31, was also called almost a million light years – too far to be part of the milky way.
Hubble’s work opened the door to the study of the universe outside our galaxy. In the century since the groundbreaking work of Hubble, Astronomers like me have learned that the universe is enormous and contains trillion galaxies.
Nature of the Nevels
In 1610, Astronomer Galileo Galilei Used the newly invented telescope to show that the Milky Way consisted of a large number of vague stars. The next 300 years, astronomers started that the Melkweg was the entire universe.
While astronomers scan the nocturnal sky with larger telescopes, they were intrigued by fuzzy light light spots called Nebulae. Towards the end of the 18th century, astronomer William Herschel Used star Map the milky way. He Catalogized a thousand new mists and clusters of stars. He believed that the Nevels were objects on the Melkweg.
Charles Messier also produced a catalog of more than 100 prominent mists in 1781. Messier was interested in comets, so his list was a series of fuzzy objects that may be seen for comets. He was planning to avoid comet hunters because they did not move through the sky.
As more data piling up, the 19th -century astronomers started to see that the Nevels were a mixed bag. Some were gaseous, star -forming regions, such as the Orion Nebula, or M42 – The 42nd object in the Messier catalog – while others were styplusters like the Pleiades, or M45.
A third category – Nevels with spiral -shaped structure – in particular intrigued astronomers. The Andromeda NebulaM31, was a prominent example. It is visible to the naked eye of a dark site.
The Andromeda Galaxy, then known as the Andromeda Nebula, is a bright spot in the air that intrigued early astronomers.
Astronomers had already speculated in the mid -18th century that some mists may be external systems of stars or ‘island universe’, but there was No data to support this hypothesis. Island universe referred to the idea that there can be huge stellar systems outside the Milky Way – but astronomers now just call these systems galaxies.
In 1920, astronomers Harlow Shapley and Heber Curtis held one Great debate. Shapley argued that the spiral mists were small and in the milky way, while Curtis took a more radical position that they were independent galaxies, extremely large and distant.
At the time, the debate was not decisive. Astronomers now know that galaxies are isolated star systems, much smaller than the space in between.
Hubble makes his stamp
Edwin Hubble Was young and ambitious. At the age of 30 he arrived just in time on Mount Wilson Observatory in South California to use the new whore 100-inch telescopeAt the time the largest in the world.
He started to take photographic plates of the spiral -shaped mists. These glass plates registered images of the nocturnal sky using a light -sensitive emulsion that covers their surface. The size of the telescope had the images made of very vague objects, and the high -quality mirror allowed it to distinguish individual stars in some mists.
Distances In astronomy is a challenge. Consider how difficult it is to estimate the distance of someone who focuses on a flashlight to a dark night. Ganos systems come in a very wide range of sizes and masses. Measuring the brightness of a galaxy or the apparent size is Not a good guide at its distance.
Hubble delivered a discovery of by Henrietta Swan Leavitt 10 years earlier. She worked at Harvard College Observatory as a ‘human computer‘Make the positions and brightness of thousands of stars on photographic plates.
She was especially interested in Cepheid -variablesThese are stars whose brightness regularly pulses, so that they become brighter and dimmer with a certain period. She found a relationship between their variation period or wrist, and their Intrinsic brightness or brightness.
As soon as you measure the menstruation of a cepheid, you can calculate the distance of how clear it seems using the reverse square law. The further the star is, the weaker it seems.
Hubble worked hard, making images of spiral -shaped mists every clear night and in search of the satisfied variations of cepheid variables. Towards the end of 1924 he had found 12 Cepheïden in M31. He calculated the distance of M31 as a wonderful 900,000 light years away, although he underestimates his true distance – about 2.5 million light years – by not realizing himself Two different types of cepheid variables.
His measurements marked the end of The big debate About the size of the Melkweg and the nature of the mists. Hubble wrote about his discovery to Harlow Shapley, who had argued that the Milky Way included the entire universe.
“Here is the letter that my universe has destroyed,” Noted Shapley.
Always enthusiastic about publicity, Hubble leaked his discovery On the New York Times five weeks before a colleague presented his paper during the annual meeting of the astronomers in Washington, DC
A growing universe of galaxies
But Hubble was not ready. His second major discovery also transformed the understanding of the astronomers of the universe. While he spread the light of Dozens of galaxies in a spectrumwho registered the amount of light with each wavelength, he noticed that the light was always moved to longer or savior wavelengths.
Light from the Melkweg goes through a prism or reflects one Diffraction lists In a telescope, which catches the intensity of light from blue to red.
Astronomers call a shift to longer wavelengths a red shift.
It seemed that these red -sheaf getting galaxies all walked away from the Melkweg.
The results of Hubble suggested how farther away a galaxy was, the Faster it went away from the earth. Hubble received the lion’s share of the credit for this discovery, but Lowell Observatory astronomer Vesto Slipherwho noticed the same phenomenon but did not publish his data also expected that result.
Hubble referred to galaxies Recessor speeds to leave the earth, but he never sorted out That they left the earth because the universe is getting bigger.
Belgian cosmologist and Catholic priest Georges Lemaitre made that connection by realizing that the theory of General relativity described a growing universe. He acknowledged that the space between the galaxies could cause the red shifts, making it look like they were moving away from each other and from the earth.
Lemaitre was the first to claim that the expansion must have started during the big bang.
NASA called his flagship room -Observatory after Hubble, and it is used to it Study galaxies for 35 years. Astronomers observe routine galaxies that are weaker and beyond galaxies thousands of times observed in the 1920s. The James Webb Space Telescope has pushed the envelope even further.
The Current record holder Is a galaxy, a stunning 34 billion light years away, given only 200 million years after the big bang, when the universe was 20 times smaller than it is now. Edwin Hubble would be surprised to see such progress.
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