The Sun: Continuous Challenges to an Old Subject
Mei Zhang, National Astronomical Observatory, Chinese Academy of Sciences
The Sun is in its middle age with an estimated lifetime of 10 billion years. The Sun has been providing us with light and heat ever since we human beings existed on the Earth. Solar physics, a field to study physical processes on the Sun, is an old subject in astronomy. Scientists have understood much of the internal structures of the Sun, such as how the Sun ignites nuclear reactions in its core to give us light and heat. This has even wined Hans Bethe a Nobel Prize in 1967.
However, the Sun continuously challenges our understandings of physics. There are still a few long-standing mysteries in the field of solar physics, awaiting brilliant scientists to decipher. To name a few, we still do not understand why the Sun’s outer and tenuous atmosphere, called corona, has million-degrees temperature. From the center to outer layers the Sun’s temperature drops to about 7000 degrees on the surface, but then suddenly it increases to a few million degrees in the corona. This has puzzled solar physicists for more than 70 years.
We also do not fully understand why the Sun produces sunspots in a periodic way, more sunspots during the solar maximums and less or none during the solar minimums, with a period of about 11 years. Scientists are also struggling in understanding why the Sun sometimes expel tons of hot plasma from the corona, coronal mass ejections as we call them and which may hit and damage our satellites when they arrive the outer space of the Earth.
Thanks to nowadays’ high techniques, we are now in a time of space science. We have been having satellites staring at the Sun for more than 20 years and they are sending back rich information. With more and more high-quality data at hand, scientists are stepping into a much better position to solve these mysteries.
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