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The Secret of Sunspot Formation: Why Are They Darker than the Surrounding Area?
Sunspots, temporary spots on the sun's surface that are darker than the surrounding area, are one of the best-known solar phenomena. Although primarily visible in the sun's photosphere, sunspots often affect the entire solar atmosphere. These spots form because the concentration of magnetic flux inhibits convection, causing the surface temperature to decrease. Sunspots usually appear in pairs in active regions and vary according to the solar cycle of approximately 11 years. The lifespan of a single sunspot or group of sunspots can range from a few days to a few months, but will eventually fade.
Sunspots can range in diameter from 16 kilometers (10 miles) to 160,000 kilometers (100,000 miles), with larger sunspots visible from Earth without a telescope.
The sunspot may be moving at hundreds of meters per second, indicating strong magnetic activity. Sunspots are accompanied by phenomena in other active regions, such as coronal loops, bulges, and reconnection events, and most solar flares and coronal mass ejections (CMEs) originate from magnetically active regions surrounding these groups of visible sunspots.
The history of sun spots
The earliest records of sun spots can be traced back to the Chinese Book of Changes, which was completed in 800 BC. In it, the "dou" and "mei" observed on the sun's surface are described, both words referring to the blocking of facets. The earliest conscious observation of visible sun spots was recorded by astronomer Gander in 364 AD. By 28 BC, Chinese astronomers began regularly recording sunspot observations in official records. The ancient Greek scholar Theophrastus explicitly mentioned sun spots in 300 BC. Later, the English monk John Worcester made the earliest pictorial record of sun spots in 1128.
In December 1610, the English astronomer Thomas Harriot used a telescope to observe sun spots for the first time, followed in March 1611 by the Frisian astronomers John and David Fabricius. Observe and report.
The discovery of sun spots attracted the attention of many astronomers, including the famous John Hevelius, who recorded 19 groups of sun spots during the Makeda Minimum in the early 17th century. In the early 19th century, William Herschel was one of the first scientists to hypothesize that sun spots were related to Earth's temperature, believing that certain sun spot characteristics represented the heating of the Earth.
Physical properties of sun spots
Sun spots have two main structures: the central shadow area and the surrounding penumbra area. The shadow area is the darkest part of the sunspot, where the magnetic field is strongest, and is nearly 90 degrees perpendicular to the sun's surface. The penumbra area is a relatively bright area formed by straight structures, and the magnetic field angle is larger than the shadow area. In a sunspot group, there may be multiple shadow regions surrounded by a single continuous penumbral region.
The surface temperature of sun spots is about 3000 to 4500 K, while the surrounding material is about 5780 K, so sun spots appear particularly obvious on the surface of the sun.
An isolated sunspot will appear brighter than the full Moon, even when compared to the surrounding photosphere. In some sun spots that form and decay, relatively narrow areas of bright material may also appear that penetrate or completely divide the shadow area, called light bridges. The magnetic fields of these light bridges are usually weaker and more intense than the magnetic fields of shadow areas of the same height. tilt.
The life cycle of sun spots
The appearance of sun spots can last from a few days to a few months, but the lifespan of the active areas associated with them is usually a few weeks to a few months. Sunspots expand and contract with movement on the sun's surface, ranging in diameter from 16 kilometers to 160,000 kilometers.
The formation and disappearance of sun spots
While the details of how sunspots form are still an ongoing matter of research, scientists generally agree that they are visible manifestations of electromagnetic flow tubes in the Sun's troposphere that penetrate the photosphere in active regions. Because the strong magnetic field blocks convection, this reduces the energy flux inside the Sun, followed by a drop in surface temperature.
The initial form of sun spots is a small dark area. Over time, they will increase in size and move closer to each other, forming more complex structures.
The lifespan of sun spots usually ranges from a few days to a few weeks. Sunspots can continue to appear despite the driving force of magnetic pressure to remove the concentration of magnetic fields. By observing the Sun's acoustic waves (local heloseismology), scientists were able to develop images of the three-dimensional structures beneath the sunspots, identifying strong downwelling currents beneath each sunspot.
Modern Observation and Application
Observations of sun spots rely on ground-based and Earth-orbiting solar telescopes that use filtering and projection techniques for direct observation. Because looking directly at the sun can cause permanent damage to human vision, amateur astronomers generally use protective filters or observe through projected images. High activity in sunspots is a source of excitement in the amateur radio community because it results in good ionospheric propagation conditions, resulting in greatly increased radio range.
Although sun spots and other magnetic processes have very little impact on solar radiation, the existence of sun spots still plays an important role in the transfer of energy and momentum in the solar atmosphere.
Therefore, the study of sun spots is not only a matter of astronomy, but also an important issue related to high-tech communications and earth climate change. So, as our understanding of sun spots deepens, will it change our view of the sun and its effects?
