 Neither Ptolemy 's Almagest nor Al Sufi 's Book of Fixed Stars noted this nebula , even though they both listed patches of nebulosity elsewhere in the night sky ; nor did Galileo mention it , even though he also made telescopic observations surrounding it in 1610 and 1617 . This has led to some speculation that a flare @-@ up of the illuminating stars may have increased the brightness of the nebula . 
