Question

Why do planets not twinkle?

Answer 1

Hint: In this question, we will know why the planets do not twinkle, the main reason behind this if the phenomena ‘refraction’. This will help us to know what happens to the light rays falling from planets to our eyes. Further, we will study about the total internal reflection, for our better understanding.

Complete answer:
Here, we know that planets shine more steadily because they are closer to Earth and so appear not as pinpoints like stars, but they appear as tiny disks in our sky. We can see planets as disks if we look through a telescope, while stars remain pinpoints.
The light from these little disks is also refracted by Earth’s atmosphere, when it travels toward our eyes. While the light from one edge of the planet’s disk might be forced to ‘zig’ one way and light from the opposite edge of the disk might be ‘zagging’ in an opposite way. So, these zigs and zags of light from a planetary disk cancel out each other, and this is the reason why planets appear to shine steadily, or not twinkle like stars.
Therefore, we get the required reason for not twinkling off planets.

Additional Information: There are some of the places where TIR or total internal reflection is seen. Some of them are mentioned following:
1. In Diamond: here, when the incident ray falls on the face of the diamond such that the angle formed by this ray is greater than the critical angle. This condition is responsible for the total internal reflection in diamond. Therefore the diamond shines.
2. Mirage: since, mirage is an optical illusion which is responsible for the appearance of the water layer at short distances mainly in a desert. Mirage is also an example of total internal reflection which occurs due to atmospheric refraction.
3. Optical fiber: in optical fire when the incident ray falls on the cladding, it suffers total internal reflection because the angle formed by the ray is greater than the critical angle. Nowadays Optical fibers are used because it has revolutionized the speed with which signals are transferred, not only across cities but across countries and continents making telecommunication one of the fastest modes of information transfer.

Note: Here we note that refraction is the reason for not twinkling of planets. Also, for a total internal reflection both the conditions need to be full fill, not only one. Further we should know the difference between reflection and refraction. Reflection is the change of the direction of wave or light to back to its original medium whereas, in refraction light slightly bends towards the normal when the medium is changed.