Celestial bodies are not perfect spheres or point masses. Their surfaces may be rough or their exact boundaries may not be clear. When we look at the stars, it can easily be said that the example we know best is the Sun, and apparently, we do not even know it as well as we think. Different ways of measuring the size of the Sun can’t quite agree on a single number.
An estimate of 695,700 kilometers is accepted for the officially accepted radius of the Sun. This number was accepted by the International Astronomical Union in 2015 and was based on observations of the photosphere, the deepest layer of the Sun’s atmosphere. This is the layer that we generally think of as the surface of the Sun and is used in models.
But that’s not the only way to measure the size of the Sun. Researchers have used many different methods to estimate the size of our star. The new study suggests a small difference for the Sun’s size, and the authors believe the Sun’s radius is larger than the official photospheric radius by a very small percentage.
Takata and Gough, researchers at the University of Tokyo and the Institute of Astronomy, applied asteroseismology to the Sun. They tracked the movement of waves inside our star, literally solar oscillations. These oscillations are known so precisely that they can be used to make predictions about the general properties of the Sun, including its size.
Sound waves called f-waves have also been used in the past to estimate radius. Using these waves very close to the surface, the researchers found a value different from the photospheric estimate. In Takata and Gough’s new study, p waves are examined. These are waves that pass through the entire Sun, including its core.
When asked about choosing this method to estimate the size of the Sun, Professor Douglas Gough said: “It’s a different method. I can’t say it’s better. It has some advantages and disadvantages. P-modes are sound waves and propagate through the Sun. So they actually give a measurement of the entire Sun. However, f mode is a surface wave and measures the surface layers,” he said.
The article claims that the Sun’s radius is 695,780 kilometers, approximately 80 kilometers larger than official records. The difference is small, but important for the high-precision analyzes humanity has made on the Sun and beyond. This could mean that the current Sun model is not entirely accurate.
Professor Gough said: “Acoustic waves measure things deeper. They give you a measurement of the radius of the Sun as seen from the inside rather than the outside. And that’s the difference. “And so two different measurements are created,” he explains.
The answer to why wave methods and visual methods give different results is not clear at the moment. Tanaka and Gough want to examine the possibility that this difference may be related to the solar cycle, the change in activity that our star experiences every 11 years.
It may be possible that the cycle further affects the Sun’s surface and brightness, thereby altering measurements of the f-mode and photosphere. However, it is equally possible that this is a deeper phenomenon and that p waves are also affected, and the cause of the differences may have to be found elsewhere.
The study was published in the Monthly Notices of the Royal Astronomical Society.
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