Both visible and infrared light are part of the “electromagnetic spectrum,” but supernovas also emit a different kind of radiation, in the form of subatomic particles called neutrinos-and today we have detectors to snare them, too. The James Webb Space Telescope, for example, records primarily in the infrared. With its longer wavelengths, infrared light can pass more easily through gas and dust than visible light, revealing targets that may be impossible to see with traditional telescopes. But we also have telescopes that can record infrared light-light whose colors lie beyond the red end of the visible spectrum. These instruments will show what a supernova would look like if we could fly close to it and look at it with our own eyes. Today’s scientists are equipped with telescopes that record visible light. Today’s astronomers are much better prepared for the next supernova than Kepler would have been-or than anyone would have been just a few decades ago. “Statistically, you can’t say that we’re overdue-but, informally, we all say that we’re overdue,” Fields says. So a gap of four centuries is a bit more than one might expect. Astronomers estimate that, on average, between one and three stars ought to explode in our galaxy every century. “That’s one of my favorite topics, over a beer,” says Brian Fields, an astronomer at the University of Illinois in Urbana-Champaign. So are we overdue for a bright, nearby supernova? In other words, it’s been a long wait-418 years since we’ve seen a star explode in our galaxy. Astronomers have also recorded many supernovas in other galaxies these are visible telescopically but would have been entirely missed by skywatchers back in Kepler’s day. The next best thing to Kepler’s supernova in recent years was the supernova sighted in the Large Magellanic Cloud, a small companion galaxy of the Milky Way, in 1987 (and designated 1987A). Astronomers can also view the remains of long-ago supernovas, such as the crab nebula, whose light first reached Earth in 1054. Or at least, the last one known to have been observed it’s possible that there have been other nearby supernovas in the interim, likely obscured by intervening gas and dust. The 1604 event was the last time that a supernova appeared within our Milky Way galaxy. We now know it wasn’t really a new star but rather a supernova explosion-an enormous blast that happens when certain stars reach the ends of their lives. That’s what the German astronomer Johannes Kepler saw in 1604 skywatchers elsewhere in Europe, the Middle East and Asia saw it too. It lingers in the sky for many months, gradually dimming over time. It’s so bright it can even be seen in broad daylight. Then one day you see a remarkable sight: A bright new star appears, and for the next few weeks it outshines even the planet Venus. The telescope hasn’t yet been invented, so you scan the night sky only with the unaided eye. Imagine that you’re an astronomer in the early years of the 17th century.
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