Last month we saw how to make a powerful solar telescope using a simple pocket mirror, a dark room, and a large plastic ball filled with mud or sand.
I had asked you to do an experiment with this solar telescope to get a large image of the sun on which you might see sunspots. I also asked you to write back to Indradhanush describing what you did and what you saw. In this article, I was planning to tell you what you can learn by observing sunspots. But there is only one problem. So far nobody has written back to tell us about their experiment. Nobody has told us about whether they have succeeded or failed in getting the sun’s image and seeing sunspots. So if none of my readers has seen sunspots, then what is the point in writing about what you can discover using sunspots ?
For this reason, I have decided to write about some other simple experiments that you can do with your big plastic ball filled with sand. I will write about sunspots only when I get at least one letter telling me about your experiment with the ball and mirror solar telescope. In the meanwhile, here are two more simple but interesting experiments that everyone can do.
Experiment 1.Take a large plastic ball, which is easily available in any toy shop. Buy a straight 30 cm long piece of aluminium or plastic tube from a hardware store. If you cannot obtain a metal or plastic tube, you can use a suitable substitute like a hollow bamboo tube about one foot in length. (The tube should be narrow and straight and you should be able to look through it to see the stars in the sky at night.). Using a hot knife cut small holes at the two opposite ends of the plastic ball . Put the hollow tube through the ball, such that the two ends of the tube stick out on both sides of the ball. Fill the ball with sand and seal the openings with sticky tape. Use a cup or a ring as the base mount for the ball in the following experiment.
At night, go out into the open and place your instrument on a high stool on its ring mount. Using it like a telescope , or like a rifle barrel, look through the tube and take aim on any star. Fix the ball on its mount such that you can see that star when you look through the tube. After fifteen minutes, without moving the ball again look through the tube. Now you cannot see the star. Why ?
Experiment 2. Look towards the north and identify the pole star (Dhruva tara) in the sky. Point your instrument so that it is aimed at Dhruva tara, and you can see dhruva tara when you look through the tube. After 15 minutes again look through the tube without moving the ball on its mount. You can still see dhruva tara.
Look through the tube after one hour, after two hours, after 25 hours, after 49 hours, after three days or three weeks or three months …without moving your ball on its mount – you will always see Dhruva tara.
This is because Dhruva tara does not move in the sky at all. (In fact it moves just a little bit, which you can hardly see, but you might be able to observe this movement with a very thin tube).
All the stars and planets move in the sky except Dhruva tara. Why ?
The next thing you need to do is to measure the angle made by Dhruva tara above the horizon. Since Dhruva tara does not move, that angle is fixed. It does not change. This angle is just the latitude of the place where you are. If you are in Simla, or Mandi, you can measure your latitude by measuring the angle of Dhruva tara above the northern horizon. How do you measure this angle ? This we will discuss in the next article, where we will also learn to make a geosynchron.