To mark the International Year of Astronomy which commemorates the 400^th anniversary of Galileo’s investigation of the heavens with his homemade telescope, the Trinidad and Tobago Astronomical Society planned Astronomical Workshops for schoolchildren. These Workshops include astronomical projects for which prizes are  awarded,  an astronomical video on the Universe and telescopic viewing.  The first Workshop was held on May 23^rd at the Imbert-Barrow Observatory, Mount St Benedict and students from Brazil High School, NorthGate College and Diego Martin Secondary School participated.

 

By a happy coincidence, 21 students and teachers from The Carolina Friends School, Durham, North Carolina, who were in Trinidad on an annual community project, were staying in the Hermitage which is  just west of the Imbert-Barrow Observatory and they were glad to participate in the final stages of the Workshop. The management of Top of the Mount, where some projects were held and videos shown, presented  a greatly appreciated Group Membership of the Trinidad and Tobago Astronomical Society  to them  at the conclusion of the Workshop and local participants very much enjoyed meeting this group and the resulting fraternization which occurred.One of the Workshop projects involved measuring the diameter of the Sun with a “pinhole camera”.

 

 

For thousands of years observant people have noticed images caused by light passing through small openings. The phenomenon was recorded in China in the 5^th century and a hundred years later Aristotle wondered why the images of the Sun obtained when sunlight passed through openings in wickerwork were round instead of angular. He also noted similar round images when sunlight passed through the leaves of trees. The Arabian physicist Alhazen studied the phenomenon and he demonstrated that it was due to the rectilinear ( traveling in a straight line) propagation of light and a similar conclusion was reached by the famous scientist Roger Bacon.

 

 

The pinhole camera resulted from these observations and it was used by Leonardo de Vinci to study perspective and  the astronomer Kepler used a pinhole camera to study sunspots. A pinhole camera is based on the formation of an image when light from an object passes through a small hole and is projected on a screen. It can be a large as a darkened room in which sunlight is allowed to come through a small opening in one wall or window to form an image of the Sun on the opposite wall or it can be as simple as the two sheets of stiff card used by Workshop participants. A pinhole was made in one of the cards and with their backs to the Sun (which must never be looked at with the naked eye as blindness can result) and some careful  positioning, an image of the Sun was projected on to a second card .

 

 

This card had a series of round circles of known diameter in millimeters inscribed on it and by careful manoeuvres the solar image was positioned inside one of these circles. The diameter of the  solar image (A) was thus determined The cards were inserted in slits in a cardboard holder and the distance between the slits was carefully measured. The distance of the solar image from the pinhole (B) was therefore also determined. 

 

 

These two determinations allowed those doing the experiment to determine the diameter of the Sun since it can be shown that the diameter of the Sun’s image divided by the distance of the image from the screen is equal to the diameter of the Sun (C) divided by its distance from the Earth (D)  or A/B = C/DThe mean distance between the Sun and the Earth was taken to be 150 million kmand  it can be seen that the Sun’s diameter C is equal to A/B x D.

 

 

Using very careful measurements,  two participants from Brazil High School , succeeded in obtaining a measurement of 1,359,000 km for the diameter of the Sun which, with such simple equipment and using a mean distance for the Sun, was commendably close to the accepted diameter of 1,392,000  km.(Their enjoyment in doing this experiment, the simple equipment used  and their happy fraternization with the students from North Carolina is very evident in the attached photographs)