Professor Chen Pengfei gave a presentation on astronomy. Astronomy studies various celestial bodies in the universe and Professor Chen focuses on the sun, which brings light and heat to the earth. Many undergraduates believe that there is nothing special about the sun, but when observing the sun through the best telescope on earth, we will find that a small sunspot on the surface of the sun is as large as four or five earths and a large number of dynamical phenomena occur within the sunspot. The sun is mainly made of hydrogen and helium. Although the amount of other elements is very small, they play a vital role in the lifetime of the sun.

Professor Chen also gave a very interesting presentation on the nuclear reactions that occur inside the sun. It seems to us that nuclear reactions are so violent that they can produce an enormous amount of energy in an instant, but the nuclear reactions in the core of the sun are so weak that the energy produced in a nuclear reactor, which has the size of an office, cannot even light up the office. However, since the sun is very big, the total amount of energy produced by it is pretty considerable. It is common knowledge that light takes about 500 seconds to reach the earth from the surface of the sun. But the time it takes for light to reach the surface of the sun from its core is much longer than most people think. The core is very dense and photons are constantly colliding with other particles as they move, so this journey takes much more time. On average, photons take 170,000 years to travel from the sun’s core to its surface. Convection is considered crucial in the study of the sun, because convection results in different angular velocities of solar rotation in regions at different latitudes and the sun rotates faster at low latitudes than high latitudes. This phenomenon has caused the sun’s otherwise sparse magnetic lines of force to be violently stretched and curled, hence an increase of magnetic field strength. The strong magnetic field leads to many famous solar phenomena, such as the high temperature of the sun’s corona, solar flares, and solar prominences. 

After sharing with us a lot about the findings of solar studies, Professor Chen introduced the methods of astronomical research: observation, theory, and simulation. Nowadays, much of the research work is about proposing appropriate models for specific problems and phenomena and later using the computer to conduct digital simulation. Nanjing University, at present, is a national leader in astronomical research. Professor Chen hopes that more students who are interested in astronomy will actively join this field.