Hans Bethe (Photo from the Nobel Foundation archive.)
I tend to say either "Hi" or "What's burning you up?" to the Sun on my morning walk. It is, of course, a rhetorical question. It is not an attempt to anthromorphize the Sun. That would be silly.
Speaking of what is burning up the Sun, Hans Bethe. The great German American physicist revealed how the Sun is like a giant nuclear reactor that produces light and heat directly responsible for life on Earth. Hence me and my morning walks and my rhetorical greetings to the Sun.
It was in 1938/39 that Bethe wrote two papers showing how stars use two kinds of nuclear reactions to power themselves up. One is where stars up to and including the size of the Sun squeeze four hydrogen nuclei together to form one helium nucleus. That produces energy. The other that is is applicable to stars bigger than Sun where temperatures and pressures are more extreme. In those cases too hydrogen is transformed into helium "but this involves a more complex cycle of nuclear reactions in which carbon acts as a catalyst", as explained the description that accompanied Bethe's 1967 Nobel Prize.
It is because of these nuclear reactions that the Sun and other stars are able to shine for billions of years. It has been my decades-long observation that most humans do not reflect on deeper realities such as the fact that we and everything else in our solar system exists because of the Sun. And within the Sun everything emanates at such elemental levels before mind boggling processes over billions of years lead to a complex life form like us. It is depressing that so much is invested in creating often something so subpar as we find across the world among humans.
It is such an astounding ability to focus one's mind on something so elemental as hydrogen and helium in the Sun the way Bethe did. Equally though the credit also goes to the British astronomer Arthur Eddington. As the Nobel Prize website explains, "Bethe’s breakthrough work stems from the British astronomer Sir Arthur Eddington’s hypothesis in the 1920s that the intense temperatures and pressures within the Sun can force the nuclei of atoms to fuse and create heavier atoms, releasing a tremendous amount of energy in the process. Drawing upon his series of articles that provided a comprehensive account of the central components of atoms and the manner in which these atomic nuclei interact with each other, Bethe applied this knowledge to understanding the stars."
So next time you happen to catch a glimpse of the Sun, remember this.