A.T. Robertson Commentary Luke 17:24

"for as the lightning, when it lighteneth out of the one part under the heaven, shineth unto the other part under heaven; so shall the Son of man be in his day." — Luke 17:24 (ASV)

Lighteneth (αστραπτουσα). An old and common verb, though only here and 24:4 in the N.T. The second coming will be sudden and universally visible. There are still some poor souls who are waiting in Jerusalem under the delusion that Jesus will come there and nowhere else.