Nilanjan
Have you ever wondered what it would be like to have no shadow? Well, if you are in Bengaluru today, you can experience this rare phenomenon for yourself. Today, August 18, 2023, is the second Zero Shadow Day of the year for Bengaluru when the sun will be directly overhead at noon and will not cast any shadow of vertical objects on the ground. This is a unique astronomical event that happens only twice a year for places that lie between the Tropic of Cancer and the Tropic of Capricorn, within the latitude range of 23.5 and -23.5 degrees. In this blog post, we will explain the science behind this phenomenon, how to observe it, and why it is significant.
What is Zero Shadow Day?
Zero Shadow Day is a day when the sun reaches its highest point in the sky, called the zenith, and aligns with the latitude of a place on Earth. This means that the sun is exactly overhead at noon and its rays fall vertically on the ground. As a result, any object that is perpendicular to the ground, such as a pole, a stick, or even a person, will not have any shadow at that moment. This phenomenon occurs only in places that are located between 23.5 degrees north and south of the equator, which are also known as the tropics.
How does Zero Shadow Day occur?
To understand how Zero Shadow Day occurs, we need to know some basic facts about Earth’s rotation and revolution around the sun. Earth rotates on its axis once every 24 hours, which causes day and night. Earth also revolves around the sun once every 365 days, which causes seasons. However, Earth’s axis is not perpendicular to its orbital plane, but tilted at an angle of 23.5 degrees. This means that different parts of Earth receive different amounts of sunlight throughout the year.
The Astronomical Society of India explains that “the Sun is almost never exactly overhead at noon, but usually transits a bit lower in altitude, a bit to the north or a bit to the south.” This is because “the Earth’s rotation axis is inclined at 23.5 degrees to the plane of its revolution around the Sun, which is why we have seasons.” Furthermore, it says “This also means that the Sun, in its highest point of the day, will move from 23.5 degrees south of the celestial equator to 23.5 degrees north of the equator (Uttarayan), and back again (Dakshinayan), in a year. For people living between +23.5 and -23.5 degrees latitude, the Sun’s declination will be equal to their latitude twice – once during Uttarayan and once during Dakshinayan. On these two days, the Sun will be exactly overhead at noon and will not cast a shadow of an object on the ground.”
The image below shows how Earth’s tilt affects the position of the sun in different seasons.
When does Zero Shadow Day occur?
The date and time of Zero Shadow Day vary for different locations depending on their latitude and longitude. Generally, it occurs around April-May and August-September for places in India. For Bengaluru, which has a latitude of 12.97 degrees north, Zero Shadow Day occurs twice a year – once on April 18 and once on August 18. The exact time of this event in Bengaluru today is at 12:24 pm, when the sun reaches its zenith.
How to observe Zero Shadow Day?
Observing Zero Shadow Day is a fun and easy activity that anyone can do with some simple objects and tools. All you need are:
- A sunny day
- A vertical object such as a pole, a stick, or even yourself
- A watch or a smartphone to check the time
- A compass or an app to find the north direction
- A measuring tape or a ruler (optional)
Here are the steps to observe Zero Shadow Day:
- Find an open space where you can see your shadow clearly.
- Place your vertical object on the ground or stand upright yourself.
- Use your compass or app to align your object or yourself along the north-south direction.
- Check your watch or smartphone for the exact time of solar noon for your location.
- As solar noon approaches, observe how your shadow becomes shorter and shorter.
- At the exact moment of solar noon, you will see that your shadow disappears completely for a few seconds.
- You can also measure the length of your shadow before and after solar noon to see the difference.
Why is Zero Shadow Day important?
Zero Shadow Day is not only a fascinating phenomenon to witness, but also a valuable opportunity to learn about the science of Earth and Sun. It can help us understand how Earth’s tilt and orbit affect the seasons, the length of the day, and the position of the sun in the sky. It can also help us appreciate the diversity and beauty of nature and its cycles. Moreover, Zero Shadow Day has cultural and astrological significance for some people, who believe that it represents a moment of balance and harmony.
We hope this blog post has helped you to get all the information about Zero Shadow Day. We encourage you to observe this phenomenon today and share your experience with us. For more updates on science and astronomy, stay tuned with us. Thank you for reading.
