Back in the olden days when canals were still seen on Mars, Professor Holden of Lick observatory observed in the summer of 1892, when Mars was near opposition, three prominent spots, or points of light, in triangle of tolerably regular shape. It made quite an impression at the time with some thinking it due to Martians signalling Earth.
I can't find any paper listing the original event by the observers although I could find a reference that Professor W.W.Campbell determined it to likely be mountain peaks that were greater then 2 miles high which would be prominently illuminated even though the surrounding landscape would be dark.
Does anyone have a good link or site with this kind of Lick observatory data?
Has anyone ever confirmed the likely explanation with more recent Mars data?