Do all 9 planets ever line up in one straight line & in how many years does it happen?
No, because they all orbit the Sun at slightly different angles. Rough line ups happen every now and then, there was one in the late 1950s and nobody noticed. The time between the most perfect possible line-ups has been calculated at trillions of times longer than the present age of the Universe. So if it has happened at some time in the past, it will take far more time than the life of the Sun to do it again. There are no line-ups of all of the planets happening in the next several years and when there are some rough ones it just means that the planets appear to be in about the same patch of sky. Nothing happens since their gravity is too weak.
