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What is parallax? Explain?

Last updated date: 29th Feb 2024
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IVSAT 2024
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Hint: Parallax is the shift in the relative position of the object that occurs due to differences in distances from the observer. Try to add examples and applications of the phenomenon.

Complete Step by Step answer:
Parallax is the shift of a point as viewed from different lines of sight. Generally, different objects exist at different distances from our eyes. So if two persons were to observe a given point against the same background, They would see the point at different positions relative to the background.
For example, let's consider 5 points A, B, C, D, E in front of a viewer as in figure 1.
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So if we were to move some distance and observe A, B, C, D, and E from another point, we see that the angle subtended by E changed the least whereas that subtended by A changed the maximum. This means that to see A, we have to rotate our head much more than that is necessary to see E.
Also, we see that the background that we used to see from P has now changed and we now see A against a different background. This shift of relative positions of objects due to change in the line of sight is called Parallax.
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The idea of parallax is useful in measuring distances. Usually, it is used to measure the distances of planets and stars. A planet is very close to us as compared to a star. So the shift in the position of the planet against the starry background is used to find the distance of the planet. Similarly, the distance to the moon, nearby stars, etc. were also found out using the parallax method.
There are also troubles that occur due to parallax - Say while measuring the distance between points using a scale or looking at the clock to know the time.
The markings on a scale are slightly above the actual point because of the thickness of the scale. So observing the point at an angle gives a higher or lower reading as in fig(3). So we have to be careful and observe the readings from directly above markings.
Similarly, clock needles are closer to us than their dial. This also causes similar effects.

Note: Parallax is used to measure positions of stars by observing the star when the earth is at the diametrically opposite points of its orbit. By measuring the angle subtended by the star at these points, and the radius of earth’s orbit, we can approximate the distance to the star.
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