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 Sun rises everyday without fail and sets in the evening without fail. Apart from this nothing about the Sun is consistent. Its rising direction changes every day so is the setting direction, only on the two equinoxes (equal nights) when 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. Time keepers 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 midday time can be early or late by more than half an hour. Later around at the time of Kepler we have learnt that all inconsistency is caused by tilt of the earth’s axis and effect of 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 was continuation of his observation of the haven using a telescope. He was not the first person to observe the Sun spots. Sun spots were reported by Chinese astronomers in 364 BC. There are early 9th centenary Arabic and European reports of Sun spots. In 1607 Johannes Kepler also observed a Sun spot. First person to telescopically observe and report Sunspots was Johannes Fabricius in 1611. But it was Galileo who proposed that the Sunspots are features over the surface of the Sun or just above it. He described that they are not permanent as the Sun rotates on its axis Sunspots are carried around and they form, appear and disappear similar to clouds but Sunspots are not made of the same ff as Earth clouds.
He also discovered the rate of rotation of the Sun and also 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 degree C cooler regions on the surface of the Sun where the visible surface of the Sun is at a temperature of about 5800 degree C. This cooling happens due to forming of a strong magnetic region, which blocks convection currents bringing hot and electrically charged plasma from the interior of the Sun where it forms in the nuclear fusion occurring in the core of the Sun. This process is affected by differential rotation of the Sun. There are years when there are no Sun spots, periods known as Solar minima and then Sunspots start appearing and their number peaks at hundreds and this period is named Solar maximum. On the average this cycle is about 11 years but can last as long as 15 years or as short as 10 years. Sunspots cycle has some longer period changes, as there was a lil in the Sunspot formation for about 50 years starting 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 where normally 40,000 to 50,000 Sunspots are observed over the same duration.
When this prolonged Solar minimum, known as Maunder minimum, was happening, Europe was experiencing a Little Ice Age. The River Thames of London used to get frozen during winters. Though this Little iIce Age started much before the beginning of the Maunder minimum, due to volcanic activity but at the same time lesser solar activity may have contributed to climate cooling. Since 1900 to 1958 Solar maximum Sunspot count trend upward. For the following years since then the trend is mostly downward. Sunspot number is observed to be related to intensity of Solar radiation since satellite measurement is available. There may be deeper and long term variations of the Solar cycle are yet to be discovered, a long minima might help us in our fight with global warming or may be not. But Solar storms produced by a prolonged and more intense maxima poses a threat to our technological civilization.
