Did you know, by comparing the shadow length in a distant city situated along the same longitude at the same time as Zero Shadow Day (ZSD) in our city, the circumference of the earth can be calculated?
Given that the weather holds up, the Second Zero Shadow Day phenomenon this year at the B.M. Birla Planetarium here can be observed on Thursday (August 3) at 12.23 p.m., informed director of G.P. Birla Archaeological, Astronomical and Scientific Research Institute K.G.Kumar here on Tuesday.
This phenomenon occurs twice a year when the sun is directly overhead and thus no shadow of any vertical object can be seen, and is because of the tilt of the earth’s axis and its rotation around the sun. This tilt causes the angle of the sun’s rays to change throughout the year, which in turn shows various lengths and directions of shadows, he explained.
The axis about which the earth rotates is tilted at an angle of 23.45 degrees to the plane of the earth’s orbital plane and the sun’s equator. The earth’s axis results in a daily variation of the angle between the earth-sun line and the earth’s equatorial plane called the solar declination.
ZSD phenomenon occurs when the sun’s declination becomes equal to the latitude of the location. On this day, when the sun crosses the local meridian, the sun’s rays will fall exactly vertically relative to an object on the ground and one cannot observe any shadow of that object.
It happens for locations between the Tropic of Cancer and the Tropic of Capricorn. The latitude of Hyderabad is 17.3850° N, hence it can be seen here on Thursday 12:23 p.m. The shadow of any vertical object would appear to disappear at this instant.
Actually, the shadow does not disappear but it is located right under the object, and in our case, it is under our feet. Subject to the weather condition and appearance of the sun, the ZSD event will be demonstrated at B.M. Birla Planetarium from noon
Mr.Kumar said interested persons can share the images of their respective scientific experiments on birlasc@gmail.com.
This day, the following places will also witness ZSD at the same time - Chiplun in Maharashtra 17.5319° N, 73.5151° E, Mandrup jn Maharashtra 17.4948° N, 75.8214° E, Akkalkot in Maharashtra 17.5242° N, 76.2054° E, and Kothagudem in Telangana 17.5560° N, 80.6170° E, said a press release.
