“If you don’t have any shadows you're not in the light” is the quote attributed to American recording artist Lady Gaga. But what if you are in bright sunshine and you still can't see your shadow? People living between the two cardinal lines of the Earth–the Tropic of Cancer and the Tropic of Capricorn, witness this every year.
Now imagine standing under the Sun holding a pencil vertical on a sheet of white card. You will see the shadow of the pencil on the white card. You can train the card towards the sun in such a manner that the shadow of the pencil falls right below it, when this happens the pencil will lose its shadow.
The earth rotates on its axis once every 24 hours. On any day, if you stand under the sun in the morning, your shadow will initially look long, stretching towards the west and as earth continues to rotate, your shadow will grow shorter. As the sun moves towards its setting point above the western horizon, your shadow will start growing longer, this time stretching eastwards. But at no point on a normal day will your shadow disappear, because although we consider noon to be the time in the day when the sun is overhead, usually the sun is never exactly overhead.
The Earth also revolves round the Sun once every 365 days, and its axis tilts by approximately 23 and a half degrees. Because of this we experience seasons and different durations of day and night. As winter comes along, the nights gradually become longer than the days. The longest night or winter solstice usually occurs around December 21. After this day, begins the Uttarayan or northward movement of the Sun. This is when the sun’s rays falls vertically on the Tropic of Capricorn and people living in that latitude will see their shadow disappear below their feet. As summer comes closer, days become longer than nights. The longest day or summer solstice occurs around June 21. After this point, the southward movement of the Sun or Dakshinayan begins and on this day the sun’s rays falls vertically on the Tropic of Cancer. Now people on Tropic of Cancer will see their shadow disappear exactly at noon.
All those living between these two cardinal lines will also see their shadow disappear but on different days depending on the latitude of their place. However, those living outside this limit will have no chance of experiencing this phenomenon. We've been calling this, Zero Shadow Day for the past decade or so.
Zero Shadow Day in your city:
May 9 – Hyderabad
May 15 – Solapur
May 18 – Pune
May 20 – Mumbai and Ahmednagar
May 21 – Nasik
May 22 – Bhubneshwar
May 27 – Surat