Astronomy Club of Ebene SSS(girls)

SUN

The sun is a star at the center of the solar system.
The sun is the largest object and contains almost 98% of

our solar systems mass.

The sun’s outer temperature is around 11,000° Fahrenheit.

The sun has been active for about 4.6 billion years and has enough fuel to keep being active for around another 5 billion years.

The Sun is not only the dominant object in the sky during the day, but it is the source of virtually all of the light and the heat that fuels life on Earth.

With a mass of 2 x 1030 kg, an atmospheric temperature of 5500 oC and a luminosity of 4x1020 megawatts, the Sun provides an excellent opportunity for astronomers to deepen
their understanding of stellar phenomena.

Sunspots were known for at least several thousands of years the Greeks knew of them at least by the 4th century BC.

The Chinese had also made some systematic observation 2000 years ago.

It was only after the invention of the telescope, in 1609 that any real study of sunspots was possible.

First seen by the astronomer and mathematician Galileo in 1613, they appear as small dark spots on the solar disk.

The theory behind sunspots

The generally accepted theory – proposed by H. Babcock in 1961 – suggests that they are caused by changes in the Sun’s magnetic field.

As the sun rotates, the magnetic fields between the poles and the equator stretches creating areas of lower temperature which are visible as dark spots.

However, they are still in the region of 4,000 ºC. By comparison, the surface temperature is around 6,000 ºC.

The spots look like craters: they are darker in the center and have a lighter rim around them.

The spots look black because they are cooler than the rest of the surface of the Sun

This darkness stems from their cooler temperatures of about 3700℃ relative to the rest of the atmosphere.

Sunspots come in all sizes. Some of them are very big, about the size of Earth, and others are much smaller.

For a spot to be visible without magnification it would have to
be approximately twice the size of the Earth.

The sunspot group seen on 22 Sept 2000, the largest for 9 years, covered about 1/500th of the solar surface, 12 times the surface area of the Earth

Their duration varies greatly.

Some last for just a few hours, while some may last for a few months (the longest in 1943 lasted for about six months.

The number of sunspots follows a cyclical period of about 11 years, something that was first noted by Heinrich Schwabe in 1843.

There are two ways of plotting this cycle.

One is to simply count the number of spots and by plotting the numbers against a time scale a periodicity can be determined.

Another is by means of the so called 'Butterfly Diagram’.

At the start of the cycle, sunspots form about 30 degrees away from the solar equator. Midway through the cycle the number of sunspots observed is maximum, and they are typically about 15 degrees away from the equator. The cycle ends with lower numbers of sunspots very near the equator.

Year (2000) was a peak of the cycle, period known as the Solar Maximum.

Sunspots are usually seen in groups of two. One set will have positive or north magnetic field while the other set will have negative or south magnetic field.

Counting sunspots

The sunspot number is calculated by first counting the number of sunspot groups and then the number of individual sunspots.

The "sunspot number" is then given by the sum of the number of individual sunspots and ten times the number of groups.

Although the 11 year cycle has been consistent in modern times, there was a period, approximately between 1645 and 1715, when there were virtually no spots at all.

This period is known as the 'Maunder Minimum’, after the British astronomer who discovered it from the records in 1890.

Scientists have not found any measurable connection between the number of sunspots on the Sun and the day-to-day variation in the weather on Earth.

Conclusion

What are sunspots?
How they are formed?
How they look like?
How to count them?
Plotting sunspots cycle?