I don't know, why did the Gnostics do it?
Nope. A lot of 19th century people claiming to see god or jesus made a lot of sacrifices. People who lie for god do a lot of complicated things.
Can you please explain this
"The Miracle of the Sun (Portuguese: Milagre do Sol), also known as the Miracle of Fátima, is a series of events reported to have occurred miraculously on 13 October 1917, attended by a large crowd who had gathered in Fátima, Portugal, in response to a prophecy made by three shepherd children, Lúcia Santos and Francisco and Jacinta Marto. The prophecy was that the Virgin Mary (referred to as Our Lady of Fátima), would appear and perform miracles on that date. Newspapers published testimony from witnesses who said that they had seen extraordinary solar activity, such as the Sun appearing to "dance" or zig-zag in the sky, careen towards the Earth, or emit multicolored light and radiant colors. According to these reports, the event lasted approximately ten minutes."
https://en.wikipedia.org/wiki/Miracle_of_the_Sun