Chinese astronomers noticed a star burning brightly in the daytime that persisted for three weeks, back in 1054 A.D.—and they weren’t alone. On the other side of the globe, Mayan stargazers recorded the same brilliant celestial phenomenon.
What they witnessed, according to famed astronomer Edwin Hubble writing almost 900 years later, wasn’t a star at all but rather the explosive death of one. That dazzling supernova would later become the Crab Nebula, and the space telescope that bears Hubble’s name recently snapped an incredible picture of it a quarter century after the first image it took.
By comparing the two images, NASA astronomers like William Blair of Johns Hopkins University can track how the nebula has evolved over time. According to Blair, the newly released image shows how the filaments of gas at the outer edges of the nebula have moved more over the past 25 years than those closer to the center. Rather than simply stretching farther outward, they appear to be moving away from the center of the nebula. That’s because at the heart of the gas cloud lies a rapidly spinning neutron star—a pulsar—whose magnetic field whips the gas into a rapidly moving whirlwind of charged particles. The outer filaments of the Crab Nebula are estimated to be moving at 3.4 million miles per hour.
Read more: “The Inside of a Neutron Star Looks Spookily Familiar”
“We tend to think of the sky as being unchanging, immutable,” Blair said in a statement. “However, with the longevity of the Hubble Space Telescope, even an object like the Crab Nebula is revealed to be in motion, still expanding from the explosion nearly a millennium ago.”
Ancient astronomers never could have even imagined getting a view like this. 
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Lead image: NASA, ESA, STScI, William Blair (JHU); Image Processing: Joseph DePasquale (STScI)
