Venus, which is in its crescent phase now, will be at its new moon phase as days progress, and make its transit across the sun on June 6. The transits of Venus are key to understanding the complex motion of planets around the sun and also help determine the size of the entire solar system and all its planets. So, it is important to observe the transit although astronomers worldwide do advise caution as looking at the sun with the naked eye or through any optical instruments causes irreparable damage to the eye.
Dr. P. Iyamperumal, executive director, B. M. Birla Planetarium, Chennai, emphasises that it is necessary to take proper precautions. He says, “The solar radiation that reaches the surface of Earth consists of many kinds of rays. The tissues in the eye transmit a substantial part of the radiation to the light-sensitive retina at the back of the eye. This might cause damage to its light-sensitive cells. The result is a loss of visual function which may either be temporary or permanent depending on the severity of the damage. Thus it is important to view the sun with caution.
Safe and simple methods
According to him, the best views of the event can be via a binocular or telescope provided these are properly fitted with astronomical solar filters. One of the simple methods suggested by Dr. P. Iyamperumal is the ‘Projection method'.
The materials needed are a mirror stuck to a piece of cardboard, a lengthy rectangular cardboard box (about 4 ft long) with openings on both sides. The cardboard to which the mirror is stuck outside is folded like a triangle. The opening on side of the box is closed with a white sheet of paper. A pin-hole as small as 5 mm is made in it. On the opposite side a rectangular paper stuck inside the box acts as a screen.
Using the small mirror sunlight is made to enter the pin-hole to form an image on the screen on the opposite side. The size of the image formed is approximately 1/100th the length of the box. The mirror which throws the light inside can be tilted to track the movement of the Sun. An important aspect of the set up is that the centre of the focusing mirror should be at the same height as the centre of the pin-hole.
Ball and tumbler
A small circular mirror is stuck on a ball and kept on a tumbler in such a way that the mirror is pointed at the Sun. A screen is kept ready in a dark room more than 10 m away so that it can reflect the image of the Sun on it. So as the transit progresses the wobbly walk of the planet across the Sun's disk will be clearly evident on the screen. The mirror is swivelled in accordance to the path of the Sun. The arrangement can also be used to view the sunspots on other days.