Max Planck Institute for Solar System Research | 2020 Apr 30
An analysis of 369 solar-like stars shows that solar brightness variations are extremely weak
The Sun is an ever-changing star: at times, numerous dark sunspots cover its visible surface; at others, the surface is completely "empty". However, by cosmic standards the Sun is extraordinarily monotonous. ... For the first time, the scientists compared the Sun with hundreds of other stars with similar rotation periods and other fundamental properties. Most of them displayed much stronger variations. This raises the question of whether the Sun’s feebleness is a basic trait or whether our star has merely been going through an unusually quiet phase for several millennia.
The extent to which solar activity (and thus the number of sunspots and the solar brightness) varies can be reconstructed using various methods - at least for a certain period of time. Since 1610, for example, there have been reliable records of sunspots covering the Sun; the distribution of radioactive varieties of carbon and beryllium in tree rings and ice cores allows us to draw conclusions about the level of solar activity over the past 9000 years. For this period of time, scientists find regularly recurring fluctuations of comparable strength as during recent decades. "However, compared to the entire lifespan of the Sun, 9000 years is like the blink of an eye”, says MPS scientist Dr. Timo Reinhold ... After all, our star is almost 4.6 billion years old. "It is conceivable that the Sun has been going through a quiet phase for thousands of years and that we therefore have a distorted picture of our star," he adds.
Since there is no way of finding out how active the Sun was in primeval times, scientists can only resort to the stars: ... the MPS researchers investigated, whether the Sun behaves "normally" in comparison to other stars. This may help to classify its current activity. ...
The Sun Is Less Active Than Other Solar-like Stars ~ Timo Reinhold et al
- Science 368(6490):518 (01 May 2020) DOI: 10.1126/science.aay3821