The astronomers use trigonometry for calculating distances to stars.  They know the diameter of the Earth’s Orbit which is 2 A.U.(Astronomical Unit).  They find out the parallax angle by simply taking two photographs in January and then again 6 months later, when the Earth has changed  it’s position in space by an amount equal to the diameter for the Earth’s diameter.  They  use accurate telescopic equipment to measure the parallax angle.
 The formula for determining the distance is as follows:
 

                                                                            Length of Arc              =      Angle
                                                                        Circumference of Circle           360'

                                                                                                 AB    = 2p
                                                                                                  2 Pi r    360'

                                                                                             r  =  360'  AB
                                                                                                      2p  2 Pi

                                                                                since 1'  =  3600 arcseconds
                                                                                           and AB = 2 A.U.
                                                                         Therefore,
                                                                                   r  =  1296000  *  2 A.U.
                                                                                             2(3.14)         2p

                                                                                         r= 206265 A.U.
                                                                                                        p
                                                                        since 1 parsec = 206265 A.U.
                                                                         Therefore,
                                                                                               r = 1
                                                                                                     p
                                                                                    where r is the distance
                                                                                        and p is the parallax angle

 Units

The parallax angle is measured in arc seconds
    1'   =   3600  arc seconds
 

 

 
 
 

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This page was created by Ahmed Javed.

 
 
 

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