Why Do Stars Twinkle?


Stars are the huge balls of hot gases present in space. The center of a star radiates an enormous amount of energy that gets radiated towards its outer boundaries. This causes heat energy to be released, which provides a glowing look to the stars. The stars present in the sky differ from each other in terms of size, color, and brightness. The color of a particular star tells a lot about its nature and characteristics such as its temperature. For instance, the stars that are blue in color are the hottest of all the other colored stars and have a temperature that is more than 30,000-degree Celcius. The white-colored stars are comparatively cooler with a temperature approximately equal to 7,000-degrees Celcius. The temperature of the yellow-colored stars lies within the range of 5,000-6,000 degrees Celcius. Similarly, orange stars have a temperature nearly equal to 3,500 degrees Celcius. The red stars are the coldest as compared to all the other stars and have a temperature value of around 2,000-degrees Celcius. Proxima Centauri is located nearest to the earth with a distance of around 40,208,000,000,000 km or 4.24 light-years away. UY Scuti is the largest known star in the universe with a size of approximately 1,700 times more than the sun. Likewise, Sirius-A is the brightest star known to us. In ancient times, while observing stars, astronomers used to group a number of stars together. This group or cluster of stars forming a particular pattern is known as a constellation. All the stars tend to appear moving along with the motion of the earth except for the Polaris, which is fixed directly above the north pole and is commonly known as a pole star. During the old days, stars were used for navigation purposes because the axis of the earth perfectly matches the position of the pole star; therefore, it helps the observer to locate the North direction on the compass.

Life Cycle of Star

Reason: Why Stars Twinkle

Twinkling of the stars is basically due to the process of atmospheric refraction. When the light from a star travels through space and reaches the earth’s atmosphere, it undergoes refraction and bends a little. This speed of the light decreases significantly as the light enters from a vacuum into the atmosphere. The human brain produces the image of the star by shifting it in the forward direction than the original position of the star. Hence, the atmospheric reflection of light leads to a phenomenon called the apparent shifting of the star. The light originating from the star does not follow a straight path to reach earth but tends to take a zig-zag path. This happens because of the uneven density of the earth’s atmosphere. The factors responsible for the uneven density are the temperature and composition of the air. The greater be the temperature, the lesser will be the density and vice-versa. Similarly, the air contains a disproportionate amount of gases and dust particles, which affect the density and hence, the speed with which the light from the star travels. Hence, the change in density of the earth’s atmosphere corresponds to a change of path taken by the light from the star, which further leads to the twinkling of the stars. The atmospheric refraction also affects the brightness of a star. When the atmosphere refracts more starlight towards the observer, it appears bright; whereas, when it refracts less light, the star appears dull.

NCERT Q10 - Why do stars twinkle? - Chapter 11 Class 10 Eye

Reason: Why Planets Do Not Twinkle

The planets do not have the light of their own, they shine with the help of the sunlight that gets reflected off their surface. To an observer standing on the surface of the earth, the planets appear to be larger in size than the stars because they are located near to the earth. The enormous size of the planets helps them to maintain constant brightness and avoid twinkling; however, in reality, planets do exhibit twinkling, but it is not perceptible to the human eye because of their huge size.

Reason Why Planets Do Not Twinkle

Tips for the Best Stargazing

1. The sky must be clear.

2. The days before, during, and soon after the new moon are best suited for an amazing stargazing experience.

3. The site chosen for stargazing must be located at a height and should be pollution-free.

4. A high-definition telescope elevates the stargazing experience.

5. One must keep track of the sky events in advance.


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