Inconsistent Sun

Inconsistent Sun

Our ancestors took the Sun for granted. Unlike the Moon, it doesn’t change its shape/phase, or its brightness on its own doesn’t change unless its light is blocked by dust, fog or clouds. In the morning, the Sun rises every day without fail and sets in the evening without fail. Apart from this, nothing about the Sun is consistent. Its rising direction changes daily, as does the setting direction, only on the two equinoxes (equal nights). When the length of the daylight time and nighttime is equal, the Sun rises in the east and sets in the west. Ancients knew about this and built structures like the famous Stonehenge to measure and celebrate the annual seasonal cycle. Timekeepers who built sundials like Samrat Yantra at Jantar Mantar also knew that the Sun’s apparent motion across the sky speeds up and slows down in different seasons so that midday time can be early or late by more than half an hour. Later, around the time of Kepler, we learnt that all inconsistency is caused by the tilt of the Earth’s axis and the effect of the elliptical shape of the Earth around the Sun.

It is only when Galileo discovered blemishes on the ‘face’ of the Sun its godly status was questioned. He reports dark spots on the disk of the Sun in his Letters on the Sunspot in 1612, which was a continuation of his observation of the haven using a telescope. He was one of many people to observe the Sunspots. Sunspots were reported by Chinese astronomers in 364 BC. There are early 9th-century Arabic and European reports of Sunspots. In 1607, Johannes Kepler also observed a Sunspot. Johannes Fabricius was the first person to observe and report Sunspots in 1611 telescopically. However, Galileo proposed that Sunspots are features over the surface of the Sun or just above it. He said they are not permanent as the Sun rotates on its axis. Sunspots are carried around, form, appear and disappear, similar to clouds, but They are not made of the same ff as Earth clouds.

He also discovered the rate of rotation of the Sun and the differential rotation of the Sun’s Surface as the Equator of the Sun rotates faster than the polar regions.

Now we know that Sunspots are about 1000 degrees C cooler regions on the Sun’s surface where the Sun’s visible surface is at a temperature of about 5800 degrees C. This cooling happens due to the formation of a strong magnetic region, which blocks convection currents, bringing hot and electrically charged plasma from the interior of the Sun, which forms nuclear fusion in the core of the Sun. This process is affected by the differential rotation of the Sun. There are years when there are no sunspots, periods known as solar minima, and sunspots start appearing, and their number peaks at hundreds. This period is named solar maximum. On average, this cycle is about 11 years but can last as long as 15 years or as short as ten years. Sunspot’s cycle has some longer period changes, as there was little in the Sunspot formation for about 50 years, from 1645 to 1715 AD. This was first noticed by Gustav Sporer and studied in detail by Edward Maunder and his wife Annie Maunder in around 1889. During this period, fewer than 50 Sunspots were observed, whereas 40,000 to 50,000 Sunspots are normally observed over the same duration.

When this prolonged Solar minimum, known as the Maunder minimum, was happening, Europe was experiencing a Little Ice Age. The River Thames of London used to get frozen during winter. Though this Little Ice Age started much before the beginning of the Maunder Minimum, due to volcanic activity at the same time, lesser solar activity may have contributed to climate cooling. From 1900 to 1958, the Solar maximum Sunspot count trended upward. For the following years since then, the trend has been mostly downward. The sunspot number is observed to be related to the intensity of Solar radiation since satellite measurement is available. There may be deeper and long-term variations of the Solar cycle that are yet to be discovered; a long minimum might help us in our fight against global warming, or maybe not. But Solar storms produced by prolonged and more intense maxima threaten our technological civilization.


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