Why Study The Sun?

The Sun is a fairly typical star in our galaxy but, most importantly to us, it is the star on which all life on Earth depends.

The Sun is also the only star that we are capable of studying “up close and personal” and, while we know a great deal about it, much is still unknown. This gives us a two-fold interest in studying the Sun. The first is to understand how changes in the behavior of the Sun affect the nature and quality of life on Earth; the second is to understand the physics behind the Sun so that we may understand the behavior of other stars that populate the universe but are too distant to observe in any great detail.

One way the Sun appears to affect the Earth is through solar-influenced climate change. The 11-year cycle of increasing and decreasing sunspot activity has been known for centuries but little understood. Historical evidence shows this cycle has stopped for unknown reasons on several occasions and that this absence of sunspot activity has coincided with significant climate changes such as the “little ice age” in Europe from 1645-1715. And, while not linked directly to the sunspot cycle, recent stratospheric wind research shows a clear solar influence, though how these upper atmospheric winds affect the surface of the Earth is not yet known.

Other solar phenomena, such as magnetic field fluctuations, including sudden explosive magnetic storms know as flares, change the properties of Earth’s upper atmosphere, often leading to widespread disruptions of radio communications. These fluctuations also cause the atmosphere to expand, causing an increase in the drag on low-Earth orbit satellites. In severe geomagnetic storm conditions, a satellite’s orbit may change, compasses on Earth may deviate, and satellite dishes may get noisy. Radiation from flares is of concern to space-walking astronauts and can even give airplane passengers amounts of radiation equal to that of a medical x-ray. And for several years now, scientists have known of oscillations at the surface of the Sun which link the solar surface to its deep interior structure.

Since 1978, a series of satellite instruments has measured the solar irradiance almost continually and has shown that the Sun’s energy output is variable on several time-scales, the most easily studied of which is the 11-year sunspot cycle, with its solar maximum and minimum. Much of the effect of this variability remains unknown but world-wide efforts are underway to understand the nature of solar activity and its effects on the Earth. Both ground-based and space-based observations and monitoring of the Sun is ongoing and the San Fernando Observatory is an active participant in this effort.