What caused the darkness?
The following snippet is a possible physical explanation for the three hours of darkness at the cross when Jesus was crucified.
It was not an eclipse of the sun because Passover, when Jesus was crucified, was a time of full moon.
During my academic work on earthquakes in Japan in the first few years of the millennium, I remembered the great earthquake at the time of the death of Jesus. It was so great that the soil ruptured and various old graves were opened. I would guess the earthquake was magnitude 7-8.
My colleague at the time, Professor Ikeya, Osaka University, told me of a 7.9 Magnitude earthquake called the Great Kanto Earthquake near Tokyo in 1923, which killed more than 100,000 people. One minute before the earthquake a large dense cloud suddenly materialised from nowhere, and was photographed (see photo). Similar clouds happened before the 1995 Kobe earthquake aftershocks and were in the 1999 Izmit earthquake, in Turkey. Details about these were included in the book about earthquake precursors which Professor Ikeya published (Ikeya 2004). Some were like fog patches in fine weather and stayed quite stationary for a significant time in spite of wind. Nobody knows the maximum time this can happen before an earthquake, and the clouds themselves are rather uncommon.
The detailed physical explanation for this is supposed to be that very low frequency pulses of electromagnetic waves created near the surface of the ground by seismic force acting on small particles of quartz cause condensation of water vapour to form clouds. Professor Ikeya was able to reproduce this on a laboratory scale.
This would certainly register to onlookers as highly unusual, and certainly be described as a darkening of the sun if you were in the cloud, but it would not be a total darkening. And could it last three hours? We don’t know, but again it suggests it is unwise to dismiss accounts of unusual phenomena just on the basis that they are unusual. Otherwise we would end saying a magnitude 8 earthquake must be an illusion because it happens so infrequently!
What would a spiritual earthquake be like?
Reference
Ikeya M. 2004. Earthquakes and Animals. Singapore: World Scientific.