To us, the Sun is by far the most important body in the heavens. It is a star out of billions of stars, but it is close enough for us to study it in detail.
By Muhammad Baqir (lecturer in physics)
Our SUN :
Although it is very important to us but, among the stars, it is a very ordinary kind of star. Inide, the Sun is much hotter. In the core, the temperature is estimated to rise as high as 15,000,000 , and the surface is at 5,500
Surface of the Sun:
Although the surface of the Sun may seem smooth to us, but actually it is turbulent, reflecting vigorous convective motion. The convective bubbles that bring energy to the surface of the Sun make the Sun’s surface look granular and these features are called “ granules’. The surface of the Sun shows a number of other features. Almost all the features seen on the Sun are controlled by its magnetic field. The features of Sun include: sunspots, solar prominences and flares etc. In this paper, we are going to focus mainly on sunspots.
Spots On The Sun:
The Sun has an activity cycle of around 11 years, during which the number of sunspots, solar flares, and eruptions rise and fall significantly.
Dark spots have been observed in the photosphere of the Sun for thousands of years. Some sunspots are as large as Earth and individual sunspots may last several weeks. In visible light, sunspots appear dark because they are cooler than rest of the photosphere. There temperature is about 3,500 while the temperature of the photosphere is 5,500
Ø Cause of sunspots:
Sunspots are known to have strong magnetic fields associated with them. The Sun’s magnetic field is so strong in the area of sunspot that the convective motion is greatly reduced beneath it. As a result of reduction of convective motion, the amount of the heat brought to the surface of the Sun (due to this motion) also reduces and hence the spot becomes cooler and appears darker than the rest of the photosphere.
Ø The 11- Year Cycle:
The position and number of sunspots varies during an 11-year cycle. At the beginning of the cycle, there are a few sunspots and they form at mid latitudes. As the cycle progresses, the number of sunspots increases and they form at lower latitudes.
The 11-year cycle has been consistent since 1710, almost no sunspots were observed from 1640-1710. This period is referred as Maunder Minimum.
Ø Parts of a Sunspot:
A sunspot is made up of two parts, umbra and penumbra. The umbra is the dark central region and the penumbra is the lighter, surrounding region of umbra.
Ø Observing Sunspots:
Sun is such a concentrated source of light that looking at it directly could cause permanent eye damage and due to its light the sunspots will not be visible with directly. So, there are two ways you can see the sunspots:
- You can point your instrument (telescope or binoculars) at the Sun and project the image on a piece of paper held behind the eye piece (where usually eye is).
- Or you can simply use a solar filter (whether fitted in the eye piece or the objective) and see the sunspots directly through your telescope or binoculars.
Here are some images which I took in 2022 of sunspots during their 25th cycle.
Ø Images of sunspots taken by me:
In this image, sunspots can clearly be seen at three different locations. This image was taken on 4-May-2022.
This is the magnified image of the sunspots at the 3rd location. Here the umbra and penumbra can be seen clearly.
As it is clear in this image that as the cycle was progressing, the number of sunspots was also increasing. Here, sunspots can be seen at 4 different places. This image was taken on 17-May-2022.
This is image was taken on 19-May-2022. With the passage of time the Sun was getting more active.
This image was taken on 20-May-2022. As it is seen that many small sunspots were also appearing as the cycle was progressing.
This image was taken on 21-May-2022, with clearly visible sunspots.
This image was taken on 26-May-2022. Here it is evident that new sunspots arose within 5 days after 21-May.