![]() ![]() In addition, orbiting solar telescopes like SDO generally collect wavelengths of light emitted deeper inside or further outside the sun, rather than its visible photosphere. Each pixel on SDO images covers about 90 miles (150 km), Wright said, which means there's a limit to how precisely the size of the photosphere can be measured with this method. Scientists have tried measuring it through transits of Mercury and Venus - when those planets cross the face of the sun - and through images taken from sun-observing satellites like the Solar Dynamics Observatory. In 2015, the International Astronomical Union defined a "unit" based on the sun's radius as a similar 695,700 km, based on a 2008 study, so researchers can use that value to compare the sizes of other stars in the universe.īut efforts to measure the sun's radius have never been accurate enough to match our knowledge of the moon's and the Earth's contours, the researchers said. The value was first published in 1891 by the German astronomer Arthur Auwers, Wright said, and it was taken as a standard value for quite some time. Historically, researchers have used the value 696,000 kilometers as the radius of the sun's photosphere - the body of the sun whose wavelengths are visible to the naked eye on Earth. "You just hold a ruler up to the sky, and you say it's this big."īut as it turns out, it's not that simple, Wright told. "How can you not know this?" Wright recalls thinking. He, too, had to scale up the sun slightly from the traditional size for his calculations to match reality. NASA researcher Ernie Wright came to a similar conclusion as he began to create increasingly precise models of solar eclipses, starting about two years ago. So it was around then that Jubier began to realize something was amiss. Scientists' knowledge of the Earth's and moon's contours weren't exact enough to highlight this discrepancy until about 10 years ago - the same time that modern eclipse simulations became possible through computer power and precision mapping. "For me, something was wrong somewhere, but that's all I could say," Jubier told. The photos helped him identify exactly where an observer had been for historical eclipses - but those precise eclipse shapes only made sense if he scaled up the sun's radius by a few hundred kilometers. He came to realize there was something off about the sun's measurements as he matched his eclipse simulations with actual photos. Xavier Jubier creates detailed models of solar and lunar eclipses that work with Google Maps to show precisely where the shadow of the moon will fall on the Earth, and what the eclipse will look like at each point. Scientists don't know the sun's size as precisely as the details of the Earth and moon, making it a sticking point for perplexed eclipse modelers. A growing number of researchers think that the sun is actually larger than commonly thought. ![]()
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