Sunspots : If you look at the photographs of the Sun, you see dark spots on its visible surface. These dark spots are called sunspots.
- Sunspots can be seen sometimes even with unaided eye at sunrise or sunset. (But you should not attempt to see the Sun with unaided eye as it may cause irreparable damage to your eyes because of its intense brightness.)
- Naked eye observations of sunspots date back to ~ 2000 years in China .
- It was in the seventeenth century that Galileo, using the telescope which he himself had fabricated, observed sunspots and found that these dark spots were in motion. This led him to suggest that the Sun was spinning in space. Galileo also observed that the sizes and shapes of the sunspots kept changing as they rotated with the Sun.
- Temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding region. They are region of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity. Their number varier according to the approximately 11-year solar cycle.
Sunspot Cycles : The observed motion of the sunspots indicates that the Sun is spinning in space. In 1843, Heinrich Schwabe, a German who observed the sky for fun, discovered a periodic variation in the numbers of visible sunspots. He found an interval of 5.5 years between the time when maximum number of sunspots (sunspot maxima) were observed and the time when the minimum number of sunspots (sunspot minima) were observed. The solar cycle or solar magnetic activity cycle is the nearly periodic 11 years change in the sun’s activity (including changes in the levels of solar radiation and ejection of solar material) and appearance(changes in the number and size of sunspot, flares and other manifestations). Another important observation pertaining to sunspot is that the sunspot zones migrate along solar latitude.
Solar Maxima : Solar minimum represents a time when sunspots number are relatively low.
Solar Minima : Solar minimum represents a time when sunspots number are relatively low.
Umbra: The Umbra is the inner, dark, cool(3700K) region of a sunspot. The Umbra of a sunspot can be upto 12000miles(20000km) wide. In the umbra, the sun's magnetic field is very strong.
Penumbra: The Penumbra is the outer, relatively light region of a sunspot. It is shaped like an ring surrounding the darker, cooler umbra.
