The massive monument built by our ancestors surprises us even today. But why they built such enormous monument to observe celestial event. Some theory like "Ancient Astronaut Theory" says our ancestor got help from alien being to build those monuments.
But it's not only theory that says extra terrestrial life visited earth in remote past. Dogon Tribe in Africa believes that they got their knowledge from alien of a star which is 80 trillion km away from earth. Today the star is named Sirius. Dogon also says there is a dark companion of Sirius orbiting it. They say extra terrestrial being came from this dark planet. They are celebrating this event for thousands of years.
The most surprising fact is that, the dark companion does exist. But it is discovered very recently in 1862 with modern equipment and technology. There are no way ancient people like dogon could have seen the dark companion with naked eyes because small dark planet gets lost in front of bright star. So it is not possible to see that. Then how did the dogon know about the star thousands of years ago? Did extra terrestrial life really visited earth in the past and share their knowledge with ancient people?