Globe

This replica depicts our place on earth and its orientation. Its axis parallel to that of the earth. It demonstrates which parts of the globe are receiving sunshine, when we have sun shine here. It also shows the day-night terminator (places where Sun is rising/setting) and how Arctic / Antarctica regions do not get any sunlight at some time of the year.

This rotatable globe is a replica of the Earth true to the orientation of the rotation axis.

When Bengaluru's position on the globe is brought on to the top, the sunlit portion exactly mimics the sunlit portion of the real Earth as seen from the outer space. and one can infer about the places where Sun is about to rise or has already risen, about to set or has already set.

On any particular day, the duration of the day can be determined by the following way. For example let us do it for Bengaluru. At the time of Meridian passage of the Sun, move the globe to a position where Bengaluru is just about receiving sunlight. Continue the rotation till Bengaluru comes to the meridian. This represents half of the duration of day. Continue to rotate till it just stops getting any sunlight. The angle through which the globe has rotated during the above interval is a measure of the duration of the day. This can be done for any location.

A similar exercise done on Summer and Winter solstices demonstrates that Arctic region receives sunlight all the 24 hours on Summer solstice where as it is 24 hours night for Antartic region. Exactly opposite to this is the case on Winter solstice

A stick placed at the position representing Bengaluru casts a shadow whose length varies with the apparent motion of the Sun. Obviously, the shadow length gradually decreases and becomes a minimum sometime around mid noon and then increases again.

On that particular day when the declination of the Sun is exactly same as that of the latitude of Bengaluru(130N), the Sun comes to the Zenith exactly at noon and the shadow of the stick completely vanishes. This is what is called a zero shadow day. For Bengaluru's latitude, April 25th and August 18th are the zero shadow days.

The fact that zero shadow day happens only to those places whose latitude is same as the declination of Sun, can be very well demonstrated by placing sticks of the same height on places with different latitudes but with the same longitude as Bengaluru for example Delhi. It can be seen that when the shadow length is zero for Bengaluru, other sticks placed at other places will have a shadow of a finite length. Since the rotation axis is aligned to the axis of Earth, Pole star can be seen through out the year during the night time through the central tube.