We have seen what we thought was unseeable. We have taken a picture of a black hole. The EHT picks up radiation emitted by particles within the disc that are heated to billions of degrees as they swirl around the black hole at close to the speed of light, before vanishing down the plughole.
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The dark shadow within marks the edge of the event horizon, the point of no return, beyond which no light or matter can travel fast enough to escape the inexorable gravitational pull of the black hole. Since then, astronomers have accumulated overwhelming evidence that these cosmic sinkholes are out there, including recent detection of gravitational waves that ripple across the cosmos when pairs of them collide. But black holes are so small, dark and distant that observing them directly requires a telescope with a resolution equivalent to being able to see a bagel on the moon.
This was once thought to be an insurmountable challenge. When observations were launched in , the EHT had two primary targets.
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The second target, which yielded the image, was a supermassive black hole in the galaxy M87, into which the equivalent of 6bn suns of light and matter has disappeared. The success of the project hinged on clear skies on several continents simultaneously and exquisite coordination between the eight far-flung teams. Observations at the different sites were coordinated using atomic clocks, called hydrogen masers, accurate to within one second every million years. And, on one night in April , everything came together. The sheer volume of data generated was also unprecedented — in one night the EHT generated enough data to fill half a tonne of hard drives.
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This meant waiting for half a year for the South Pole data, which could only be shipped out at the end of Antarctic winter. Their calculations, however, laid important groundwork for future astronomers and led to some of the most important astronomical discoveries. Cannon simplified two earlier schemes into one that astronomers still use today.
Over the course of her life, Cannon classified the spectra of over , stars—legend has it that she could look at any stellar spectra and classify it in just three seconds.
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The tool she used to observe spectra is in front of her. Image: Smithsonian Archives. Working alongside Cannon was Henrietta Swan Leavitt.
Constantly battling illness and hearing loss, Leavitt was only able to be sporadically employed at the Harvard College Observatory. These ailments, however, did not stop her from making one of the most important astronomical discoveries of the 20 th century.
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Leavitt studied variable stars, which vary in brightness over the course of days, weeks, or even months. Leavitt discovered a number of these stars in the small Magellanic cloud, two irregular dwarf galaxies visible from the southern hemisphere, and published her results in the Annals of the Astronomical Observatory of Harvard College in Notably, by applying this relationship to Cepheid Variables found in the Andromeda nebula, Edward Hubble discovered that it was so far away, it had to lie outside of the Milky Way—making it the first galaxy to be discovered.
Are we alone? Sadly, Sagan met significant resistance from many of his scientific contemporaries for his tireless work popularizing the value of science and space exploration, and was reportedly denied membership in the National Academy of Sciences because of the petty jealousies of other scientists.
While the task of compressing space history into just milestones is a herculean one, The Space Book accomplishes it with admirable rigor, breadth and balance — a feat at the intersection of the editorial and curatorial: on the one hand, the short page-long essays on each of the milestones offer beautifully synthesized background and insight on how the specific person, event, or idea shaped the course of space history; on the other, the very act of selecting and ordering such notable nodes is itself a masterful creative accomplishment.
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Bell observes a curious pattern that reveals a crucial paradigm shift in the evolution of science and the shift toward the cross-pollination of disciplines: I noticed partway through the research that the number of individuals being singled out for mention was decreasing over time, especially in the entries after the s — the start of the Space Age.
go to link Carl Sagan — astronomer, planetary scientist, author, science popularizer, and host of the acclaimed television series Cosmos — next to a full-scale model of the Viking Mars Lander in
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