On June 8, 2004, the transit of Venus (TOV) will be visible from most parts of the world. The entire transit will be visible from India. Occurring after 121 years, there is nobody alive today who has witnessed a TOV. None occurred in the twentieth century.

In the history of science, the TOV occupies an important place because it was the first time in human history when the astronomical unit (AU), the distance of the Sun from Earth, was measured with reasonable accuracy. Measuring the astronomical unit was the missing link in the edifice of Newton’s Solar System. This was first achieved in 1761. The distance of the Sun from Earth was something that Newton and Galileo did not know.

That TOV can be used to measure the AU was proposed in a paper by Edmund Halley. Halley could not implement his proposal, because no TOV occurred during his lifetime. Halley’s method involves some delicate measurements and fairly arduous spherical trigonometrical calculations.

It is well known that in 1639 Jeremiah Horrocks was the first human being to observe a transit of Venus. What is not so well known is that he also attempted to measure the AU during that experiment using Venus as a gauge. For this he had to make a simplifying assumption about the relative sizes of Earth and Venus. He made the wrong assumption- that both Earth and Venus subtend the same angle at the Sun, and ended with a measure for the AU which was about 40% too small.

With another, equally plausible, but different assumption, however, the measurement of the AU becomes so simple that any eighth standard school student can do it. This booklet tells you how this can be done by anyone. This gives rise to the possibility of a mass scientific experiment on June 8th 2004, involving millions of school students all over the world. In this booklet, the series of activities for this mass scientific experiment is outlined in a form that can be used by any school teacher or high school student.


MEASURING the UNIVERSE with a STRING and a STONE.

In the third century BC a Greek scientist Eratosthenes first measured the size of the Earth. This was undoubtedly one of the ten greatest scientific experiments of entire history. However, it appears that Eratosthenes did not discover the method he used. It was discovered two hundred years earlier by a man named Anaxagorus, who was trying something else, something bigger, something far more ambitious.

Anaxagorus lived at a time when the Greeks were beginning to systematize geometry. As everybody knows, geometry arose from measuring land.

Anaxagorus had the crazy idea of putting together geometry and astronomy to measure the universe. He wanted to obtain both the distance of the Sun from Earth, and its size. He got an answer of about 6500 kilometers for the Sun's distance, and about 60 kilometers for the size of the Sun. So sure was he of his calculations that he was willing to pay the heavy personal price of banishment for standing by his predictions.

Both his answers were wrong, of course, though there was no error in his calculations. The only mistake was in one of his assumptions. Anaxagorus assumed the world was flat. Though he was wrong, he had obtained the right answer to a different question - the question answered by Eratosthenes two hundred years later - "How big is the Earth”?

Eratosthenes put in the right assumption - that the Earth was a sphere, and deduced that 6500 kilometers was not the distance of the Sun, but the radius of the Earth.


How far is the Sun ?

This question remained a mystery for thousands of years till the 18th century and beat the best minds. Even the great Galileo and Newton did not know the answer to this basic question. But Anaxagorus was right in one important point. He had discovered that the Sun is approximately 110 times as far as it is big. He may have been wrong, but what he had done was among the greatest of breakthroughs in science.

An Extraordinary Possibility.

Nobody can taste science merely by reading books. The only way to taste science is to do it. The thrill of discovery is even sweeter than the joy of doing . The year 2004 offers us an extraordinary possibility : Every child in school who knows eighth standard mathematics will be able to do and understand for himself / herself two of the ten greatest scientific experiments of human history to answer the following questions.

- How big is the Earth ?
- How far is the Sun ?
- How big is the Sun?

To answer the first question, we will have to observe the beautiful sight of the Sun setting into the ocean on a clear day at a beach on the west coast of India. To answer the second and third question, we will have to observe the Sun on a very special day : the 8th of June 2004. On that day will occur the extremely rare Transit of Venus.

Between now and June 8, 2004 we will have to do a few more simple experiments. To do these great experiments in science we will not need any fancy expensive apparatus. We will need a string and a stone, a pocket mirror and a watch. But even if we don't have a watch it doesn't really matter. We can make one with a string and a stone.

This site has two parts. In part A we learn how to construct a low cost / high magnification solar observatory to observe the transit of Venus. In part B we the TOV to measure the distance of the Sun from Earth. And we will have to learn a little mathematics as follows:

1. What is an angle? How can we measure angles with a string and stone?
2. What is a ratio of two numbers?
3. The sum of the angles of a triangle is always the same.
4. Similar triangles and their properties.
5. How to deal with large numbers?
6. The importance of approximation.
7. Pythagorus theorem.

We measure the universe by measuring angles, lengths and time intervals with the string and the stone. That’s all. That’s how simple it is.

- Dr. Vivek C. Monteiro
  January 26th 2004