It’s a Zero Shadow Day (ZSD) on April 24 and Tamil Nadu Science and Technology Centre is helping Chennai students understand scientific facts associated with ZSD and collaborate with other city students across the country.
An introductory programme on observational methods was recently conducted for about 60 school students by Niruj Mohan Ramanujam, former Scientist, National Centre for Radio Astrophysics. The same set of students will attend the observational activities on April 24 and will share their shadow and time measurements with students in Bengaluru, Mangaluru, Delhi, Jaipur and Allahabad.
S Soundararajaperumal, Executive Director, Tamil Nadu Science and Technology Centre, said that they have proposed to re-enact ‘Eratosthenes Method’ by exchanging the measurements amongst the students on April 24.
The children in Chennai will measure the length of the shadow cast (which will be almost zero on April 24 at noon, that is when the Sun crosses the local meridian. Local meridian is the imaginary line connecting south, overhead and north) by the vertical stick of standard length (say 30 cm). Students will also note the instance of time at which the shortest shadow occurs.
The students in Bengaluru will conduct a similar experiment. The time of local noon, that is the time at which the shadow is the shortest, will not be the same as Chennai. At Bengaluru, this may happen about 10 minutes or so later as it is situated west of Chennai. Mangaluru local noon will occur after Bengaluru. In Delhi, Allahabad, Srinagar and Jaipur, there is no ZSD as they are away from (north of) tropic of Capricorn. However, they will measure the length of the shadow. By way of carrying out the shadow measurements and comparing them, students could estimate the speed of linear rotation of the Earth at a given latitude and the radius, the official said.
When the Sun is exactly overhead at noon, the length of the shadow cast by the objects will be almost zero. Every place on the Earth that is, between the Tropics of Cancer and Tropics of Capricorn, will have two days in a year where the Sun will be directly overhead. For India, this day happens during the time period from April to September.
On this Zero-Shadow Day (ZSD), a vertical pole will cast almost no shadow and will cast a longer and longer shadow as we move away from this day. Usually, the Sun transits a bit to the north or a bit to the south. This Zero Shadow Day will be different for different places (different latitudes).
