. Explain the parallax method for measuring large distances
With the help of it, explain the method to determine the shape of a heavenly body.
Here, the diagram
Length: It is defined as the difference between two positions taken by two events that occur instantly.
(i) Parallax Method: When an object is seen by closing our right and left eye alternatively, there is a shift in the position of the object w.r.t. the background observed.
This is known as parallax. Imagine an object P placed at a distance x from our eyes. Let the line joining the object to the left and right eye make the O angle w.r.t. each other.
O is called parallax angle. The distance LR is called basis.
(ii) Size of Astronomical Object: Diameter of Moon: Let Moon be the astronomical object whose diameter is to be measured. We observed the Moon with the help of a telescope.
Let it be observed from a place F on Earth and make an angle 0 with the two ends P and Q of the moon and the point K, as shown in fig. 1.5. 0 is called the angular diameter of the Moon.
Lt d be the distance of the Moon from the Earth.
(iii) Reflection or Echo Method: A gun is fired towards the hill and the time taken between the instant of firing and hearing of echo bet. In this time interval,
sound first travels towards the hill from the place of firing and then hacks from the hill to the place of firing.
Let u be the speed of sound. x be the distance of hill from the place of firing the gun, then