Why is VENUS TRANSIT RARE?? - The Facts behind its RARE occurrence

           A Transit of VENUS means the Planet VENUS passing directly between the SUN and the EARTH. This is a very RARE ALIGNMENT of STARS which occurs in our Solar System.

             The Speciality of this Event is the Frequency of its OCCURRENCE. The Occurrence of this event is not UNIFORM. This Transit of VENUS occurs in PAIRS.  The Transit took place in 2004 and after 8 years its happening again now ( June 2012). We can't see this TRANSIT again because we have to wait for another 105 years for another PAIR of TRANSITS with 8 years of gap between them. Then the pattern repeats (121 ½ , 8, 105 ½ , 8).



         The INTERESTING FACT here is the frequency of occurrence. The Transit is the passing of the VENUS between SUN and EARTH. Both EARTH and VENUS are orbiting the SUN. Venus takes 225 days and Earth takes 365 days to orbit. Because EARTH is Slower, Venus will definitely OVERTAKE EARTH every 1.6 years. But the Transit doesn't take place every 1.6 years. The FACT behind this Confusing thing can be understood with an ILLUSTRATION.

          Imagine two Boys running around a Cricket Ground.First one is running around Inside the STADIUM and the other is running around the STADIUM. Which means the second boy has to run longer distance to complete one REVOLUTION. If both of them are running at same speed, then the boy running inside will overtake the one running Outside. The same thing occurs in our Universe. Venus overtakes Earth every 1.6 years. But we don't see TRANSIT every 1.6 years.

        Now, imagine the STADIUM is in the Shape of the PAPER PLATE shown below.

          If the boys are running around on circles which are on two different PLANES ( Straight one and inclined one) as in the Picture. They will come FACE to FACE only when the First one overtakes the Other at the points where the two PLANES meet. This point is called a NODE and there are two nodes. With reference to paper plate it is the points where the paper is left un torn.

      Another Fact is the ORBITAL SPEED.  Most of the time when these two planets meet, VENUS completes little earlier. So each fifth time both the planets come face to face, they fall little short. In 2004 the pass alignment was just ahead of the edge of the SUN and so we saw the Transit. This year (2012), Venus has passed near the other edge of the SUN.

      In 2020, Venus will be very far above the edge of the Sun and so we cant see it. We have to wait till 2117.

       Venus crosses over Earth every 1.6 years but the LEVEL (height) at which it crosses differs. Either Venus is high above or Low below to come in line with both SUN and EARTH.

 This is why the TRANSITS happen so RARELY