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Shara et al. Nature 2017

Astronomers have identified the source of a stellar eruption observed by Korean astronomers in 1437 — and, as a result, new evidence for how certain types of stars evolve.

The history: In the 15th century, royal astronomers in Korea recorded a bright star that appeared in a constellation and, 14 days later, disappeared. Modern astronomers know that short appearance meant it wasn't a supernova but a classical nova.

Fast forward 550 years and, in 1986, Michael Shara from the American Museum of Natural History publishes a paper suggesting classical novas — unique stellar explosions in which the star ejects a layer from its surface — and dwarf novas were the same stars but at different stages of their evolution. Classical nova erupt every couple thousand of years so proof could only be found in centuries-old astronomical records. On and off for 20 years, Shara looked for the evidence in the constellation the Koreans noted but came up with nothing. "It just wasn't the right place," says Shara.

What they did: When Shara took another look about 18 months ago using new data from telescopes, he expanded his search to others stars in the Scorpius constellation — and found a star that supported his initial idea. When he put an image of it from 1923 on top of one from 2016, he could see how much it moved. He worked backward along its path over the past 580 years and "Bang! There it was!", he says. "We show that, almost 500 years a classical-nova event, the system exhibited dwarf-nova eruptions... We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions," the authors wrote.

They also found the star continues to explode in a cycle of hibernation and eruption that could be seen in photographic plates from the 1930s and 40s.

Sound smart: Classical nova and supernova aren't the same. The latter undergoes a core-collapsing death while the outbursts of classical nova are eruptions from their surface that repeat — and the star lives on.

Go deeper

"Atmospheric river" to whiplash Northern California from drought to flood

A map depicting 24-hour preciptation forecast (inches) ending Monday at 5a.m. local time. Photo: NOAA

A series of powerful "atmospheric river" storms are set dump historic amounts of rainfall across parts of drought-stricken California and the Pacific Northwest from this weekend, forecasters warn.

Why it matters: A strong atmospheric river, packing large amounts of moisture, is predicted to whiplash Northern California from drought to flood.

10,000 trees near giant sequoia groves to be removed after fires

A firefighter looks up at a giant sequoia tree after fire burned through the Sequoia National Forest near California Hot Springs, California, on Sept. 23. Photo: Patrick T. Fallon/AFP via Getty Images

"Upwards of" 10,000 trees near giant sequoia groves have been "weakened by drought, disease, age, and/or fire" and must be removed in the wake of California's wildfires, the Sequoia and Kings Canyon National Parks announced.

Why it matters: The damage to these trees, considered "national treasures," and work to remove them means a nearby key highway must remain closed to visitors as they have "the potential to strike people, cars, other structures, or create barriers to emergency response services," per a statement from the national parks.

Obama stumps for McAuliffe, urges Virginians not "to go back to the chaos"

Photo: Win McNamee/Getty Images

Former President Barack Obama framed a Nov. 2 gubernatorial race as a bellwether for the Democratic Party and the country, telling a crowd at a campaign event for Terry McAuliffe on Saturday that "I believe you, right here in Virginia, are going to show the rest of the country and the world that we're not going to indulge in our worst instincts."

Why it matters: With just over a week to go before Election Day in the Commonwealth, McAuliffe is bringing out the big guns. The 44th president appeared on the campus of Virginia Commonwealth University to urge supporters to get to the polls.