Zero Shadow Day

Alok Mandavgane

About this app

Zero Shadow is a phenomenon when the sun is exactly overhead and the shadows of symmetrical and vertical objects vanishes. This happens for locations between the tropics and is caused by the northern and southern motion of the sun during the course of a year. This app helps you find the Zero Shadow Day for any location.

If you are between Tropic of Cancer and Tropic of Capricorn, then on a particular day (one during Uttarayan and other during Dakshinayan) the Sun will pass directly overhead at local noon. At local noon on this day, a vertical pole will cast no shadow. These are called Zero Shadow Days, or ZSD. This app is an aid to the campaign by the Public Outreach and Education Committee of the Astronomical Society of India for celebrating ZSD.

Inputs and Content by
Dr. Niruj Mohan Ramanujam, ASI POEC
Translations by:
Kannada - Dr B.S. Shylaja of Jawaharlal Nehru Planetarium Bengaluru and Mrs. Jyotsna
Telugu - Teja Teppala
Marathi - Dr. Aniket Sule, HBCSE, ASI POEC.
Hindi - Alok Mandavgane
Spanish - Alvaro Jose Cano Mejia from Colombia
Portuguese Brazilian - José Roberto Vasconcelos Costa

Ratings and reviews

Very good app, it tells you when the sun will be directly overhead at your location in the tropics. Very good app, but highly specialized.

Gets the job done! Simple to use. Teaches important concepts in astronomy. It would be nice if the app author could provide resources as how to calculate the zero shadow day ourself for those who want to learn to do it.

Such a fantastic app and thank you to the Astronomical Society of India for releasing it. It has really helped me visualise how the equation of time and analemma affects sunset times here in Singapore. So happy to have found this. Thank you!

What's new

Fix for zsd info not showing.
Now you can calculate distance between two places by long pressing on other location. The shortest distance from the chosen location will be shown in the zsd info page