They sequentially moved to the places stated as visited by Shri Ram in the Valmiki Ramayan.Starting from Ayodhya, they went right up to Rameshwaram.
Only six of the twelve constellations remain above the horizon at the same time.
So far history of the world, particularly of Indian subcontinent, is based on linguistic guesswork and religious beliefs/hearsay.
However, during last 30-40 years, several new scientific tools and techniques have been developed, which are capable to determining the dates of any ancient events in scientific and precise manner.
On the basis of planetary configurations described in various other chapters of Valmiki Ramayan, the date on which Ravana was killed works out to be 4th December 5076 BC and Shri Ram completed 14 years of exile on 2nd January, 5075 BC and that day was also Navami of Shukla Paksha in Chaitra month.
Thus Shri Ram had come back to Ayodhya when he was 39 years old (5114-5075). Ram Autar, have researched on places visited by Shri Ram during 14 years of exile.
Such northward migration continued for several centuries and finally when these people from south India reached the banks of Himalayan Rivers, they got climatic conditions conducive to long term development of civilization on the banks of these rivers providing security of water, food and shelter for a very long time.