Question
Wed June 06, 2012 By: Shalini

what is radians?? and explain breifly rhe method of finding the distance between earth and moon if thet give diameter and parallatic angle!! i couldnot follow a bit!! All those new term i wasnt aware !! kindly help me

Expert Reply
Wed June 06, 2012

One radian is the angle of an arc created by wrapping the radius of a circle around its circumference.

In this diagram, the radius has been wrapped around the circumference to create an angle of 1 radian. The pink lines show the radius being moved from the inside of the circle to the outside:

            

How to use parallax to measure a distance

First you'll apply the method of parallax to measure the distance from your eyes to a finger that you hold with stretched arm in front of you. Look with one eye at the finger, and look for a mark on the wall or outside, that is just behind the finger. Remember that mark, now look with your other eye at your finger, behind it there will be another mark. The situation is like in the drawing below. When you look now at the marks without looking at your finger, you can measure the angle ß with your angle-measuring tool.

 

In this drawing a is somewhat greater than ß, but more the marks are far away, more the angles a and ß become similar. (Show this by yourself.) When you consider a = b, you know the angle in the top of the triangle that is formed by your two eyes and your finger. When you consider this a isosceles triangle, with the distance between your eyes as baseline, you can draw on scale the whole triangle and, with the help of a ruler, measure the distance from your eyes to your finger.

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