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Sun Spots

Sunderstanding : Understanding the Sun

1. Sunderstanding is a campaign. The purpose of this campaign is to take scientific thinking wherever the sun shines, to take doing and discovering wherever the sun shines.

2. The sun has been described aptly as a wonderful laboratory that no nation on earth will ever have the resources to build. Yet it is available for experimentation to the remotest village of the poorest nation in the world. A most wonderful laboratory which is available to literally everyone. There is probably no branch of physics for which the sun does not hold superb unsolved problems. Yet there are simple and non trivial experiments that even primary school children can perform , take delight in, and learn a lot from.

3. The phenomenon of the solar maxima - i.e. the sunspots maximum period which occurs once every 11 years and is currently happening for the next few months at least, the phenomenon of the total solar eclipse(TSE) which will occur in June this year, and the transit of Venus which will take place three years hence and which is a once in 243 years phenomenon, are all exciting events which can challenge and turn on school children all over the world. The transit of Venus will allow us to measure the distance between the earth and the sun. But first we have to popularise low cost and no cost (LCNC) ways of imaging the sun. This is why we thought of proposing an ongoing campaign- Sunderstanding which will attempt to reach every school child and all sections of the public.

4. In 1995 and 1999, we had participated in the very successful TSE mass campaigns. We identified four reasons for the success of the campaign :

a.A new and strange phenomenon, outside of everyday experience.
b.Some simple activity that everyone can do to view and enjoy it.
c.The involvement of scientific institutions and science
popularisation organisations.
d.Support from the mass media.

We were further encouraged to find out that solar activity and sunspots have an 11 year cycle and the maximum of the cycle would begin around the middle of 2000, lasting for a whole year. What a fine opportunity for conducting a really extensive mass do and discover campaign ! But there was a precondition. The cost of seeing sunspots had to be brought down to as low as possible. If sunspots could only be studied with expensive telescopes, there was not much chance of a real mass campaign reaching all people.

We started working on a cheap telescope kit, trying to replicate what Galileo had done in 1610 to first discover sunspots. We did succeed in designing a low cost simple telescope.

More interestingly, we found out, by doing and discovering , that telescopes are not necessary to see and study sunspots. We discovered the ‘Very Long Focal Length’ lens approach for projecting sunspots with a single lens. We experimented with mirrors and succeeded beyond our expectations. In March 2000, we discovered that CST Railway Station is a giant pinhole camera where anyone can see sunspots for the price of a platform ticket. Aiming at low cost sunspot viewing, we overshot and reached no cost sunspots. Now, a mass campaign really was possible.

One question arose. Why had it taken so long in history to discover sunspots ? Haven’t there been tall buildings with leaking roofs for thousands of years ? Didn’t our ancestors realise that the circular patches formed are images of the sun? Didn’t they look closely at those images ? We will not be surprised if some historical scientific texts are discovered which show that Galileo was not the first to discover sunspots. Many questions about the history of science are thrown up by the simplicity of sunspots.

It remains a fact that as of today (Feb 2001),very few people have actually seen sunspots with their own eyes. We hope that by the end of 2001 very few people will not have seen sunspots. Because, stubbornly countering the prevailing economic trend to confine and package knowledge and education , which can then be sold to those with sufficient purchasing power, the sun is available to everyone. With the methods in this workshop, it will be possible

to perform non-trivial scientific experiments and see sunspots at no cost even with a little piece of broken mirror.

As we write these words the sunspots have become so big that on some days you can actually see them with your own eyes, without magnification, if you look carefully at the sun with a good quality solar filter , tested for safety.***


According to the Encyclopaedia Brittanica, “With the invention of the telescope, Galileo Galilei, Johannes Fabricius, Christoph Scheiner, and Thomas Harriot almost simultaneously(1610-1611) discovered sunspots,but it was the genius of Galileo that recognised their true nature as solar phenomena.”

Duncan Steel in his recent book ‘Eclipse’, writes : “ For centuries large sunspots had been observed with the naked eye by the Chinese when dust storms blew in from Central Asia, blanketing parts of northern China. They had similarly been noticed in Europe, but it was only when telescopes appeared in the seventeenth century that continuous monitoring of these dark markings on the solar surface was feasible.”

We disagree. Observation and continuous monitoring of sunspots is possible without a telescope by a number of low cost/ no cost (LCNC) methods. You can see sunspots on the railway platform at CST, without any telesope. (The image at CST railway station is the result of the principle of the pinhole camera)

A telescope is an instrument to gather and concentrate the light reaching us from astronomical objects like the planets and stars which is extremely faint. But the sun is different . Its light reaching us is not too faint but too strong. It does not need to be gathered and concentrated . If anything, its intensity needs to be reduced .We can study and understand many wonderful things about the sun without using a telescope.


A Black box viewer which can be easily made out of a cardboard carton is a most useful device for observing the sun outdoors. To begin with, intriguing problems can immediately be posed to the students about the shapes of images from differently shaped apertures. Why do these become circular when the distance is increased. The shapes of the images cast by mirrors of different shapes also makes a fine introductory experiment. The kids can learn about angles, inverse square law, etc. by doing and discover experiments with this simple apparatus.


To view sunspots the VLFL lens method is both elegant and simple.

It is commonly believed that a convex lens concentrates the light from the sun. This however is true only if the focal length of the lens is not too large. As the focal length of the lens increases the size of the sun’s image increases. For a very long focal length (VLFL), the diameter of the sun’s image disc can be quite large, larger than the lens itself.( In a pinhole camera also, the size of the image depends on the distance of the screen from the pinhole).

In general the following formula is true :

diameter of the sun’s image disc = ½ degree
2 x pi x f 360 degrees
(This is because the sun subtends an angle of about ½ degree at the earth.)

From this we deduce :
diameter of sun’s image (in cm) = 2 x 3.14 x 1/ 720 x focal length in cm.

For a 50 mm diameter lens with a focal length of 6 metres, the image of the sun will be larger than the lens itself, showing that a convex lens doesn’t necessarily concentrate light. Using a VLFL (very long focal length) convex lens, along with a cardboard shade with a hole cut in the centre , you can get a nice big image of the sun on which sunspots are clearly visible, if the lens is of reasonably good quality.


This is by far the cheapest, but not the easiest, method to project sunspots, which works because the sunlight intensity is so strong. This experiment can be done in any room which has a window or door opening outside, and which can be sufficiently darkened by putting cloth over the apertures from where light enters. Complete darkness is not necessary. Just how much darkness is needed you can discover for yourself by trial and error.

Take any available small mirror (like a face mirror selling on the footpaths for Rs 10) and keep it on a stool outside the room in a place where the sun shines on it. Adjust the angle of the mirror so that the sunlight is reflected in a bright patch on a wall of the darkened room. Increase the distance of the mirror so that it is about 20-25 metres from the wall. As you increase the distance the light patch will become more and more circular. This is the sun’s image with the mirror acting like a large ‘pin hole’. At this stage the sun’s image will be bright and diffuse, i.e. not sharp.

The next stage is to take an opaque piece of card paper and punch a hole in it of around 2-3mm diameter with an ordinary paper punch. Now hold this paper about 30 cm in front of the mirror so that the punched hole is in the centre of the light patch which now forms on the card paper. What happens to the image on the wall 20 metres away ?

Surprisingly, the image does not decrease in size. It becomes dimmer and sharper. Cut off as much light as possible in the room(except of course the light coming from the mirror) so that the image looks clearer. Now keep a white piece of paper on the wall so that the image forms on this white screen. The sunspots should be clearly visible on this image during this period of sunspot maximum.


You can study how sunspots move by taping the white paper screen to the wall and tracing the outline of the suns disc. Mark the position of the sunspots and write the date next to it. Next day again form the image of the sun so that it exactly fits the circular outline. Again mark the date and position of the sunspots, which will have moved. Do this experiment every day for several weeks.

You will discover that after about four weeks the large sunspots return to their original locations. Some of the smaller sunspots may not last four weeks. You will discover the rotation of the sun, that the sun has a tilted axis of rotation, an equator and poles just like the earth. (Remember however that the direction of rotation is changed by reflection in the mirror, and the image is again inverted by the pinhole camera effect. Figure out the real direction of rotation.)


You can make a simple telescope with which to project sunspots. Though you can look directly at the sun through the telescope with a proper filter, we do not recommend this method as most common filters are not safe, and a telescope concentrates light making eye damage more likely. Galileo, in later life, became blind.
A simple telescope can be made with only two lenses. The front lens(objective) is long focal length (about 1 metre is ideal), and the eyepiece should have a short focal length of around 5 cm or less. You will also require one long tube (1 metre), and one short tube which slides inside the longer tube with some packing. (see fig )

The magnifying power of the telescope is given by the following formula :

focal length of the objective i.e. for 1 metre and 5 cm., the magnification is 20.
focal length of eyepiece

The telesope can be used for projecting sunspots as shown in the figure. The advantage of this method is that with good lenses you can get excellent resolution and study some details of the sunspot structure


Here are some questions that we can pose for the Sunderstanding campaign. Many of these questions can be answered by experiments with everyday materials. Some experiments may require the cooperation of friends and colleagues in different states and countries. But today with internet communication reaching every district and taluka this can be done easily and quickly. Some questions have not yet been answered by LCNC methods. But maybe if we think and work hard at it, we will discover new LCNC methods to answer questions that have hitherto required expensive and sophisticated equipment.

1. How big is the sun ?
2. How far away is the sun ?
3. How heavy is the sun ?
4. What can we understand from studying shadows cast by the sun ?
5. How hot is the sun?
6. What is the sun made of ?
7. How much energy is released from the sun ?
8. How does the sun move ?
9. How does the earth move with respect to the sun ?
10. What are sunspots ?
11. What emissions from the sun can be observed other than light emissions?
12. How does the solar activity affect events on earth ?
13. What is the structure of the sun ?
14. How much energy reaches us from the sun ? How can we use it ?


There are seven colours in the rainbow. The Brainbow, however has nine colours, two more than the rainbow.

What is a Brainbow ?

A rainbow is caused by the bending of light by raindrops.

The brainbow is caused by the stretching of your brain and the bending of your mind by the following problem :

There are twenty seven cubes consisting of nine sets of three, each set of a different colour. Arrange these cubes into a 3x3x3 cube such that on each of the six faces, all the nine squares are of a different colour i.e. no two squares have the same colour. Is this possible ? If not, why not ? If yes, then show how.


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