The 149th book by the award-winning mathematician - author Evangelos Spandagos. It is the astronomical work of the great Ancient Greek mathematician and astronomer from Bithynia in Asia Minor, Theodosius (1st century BC) titled: "On Days and Nights".

The introduction, the restoration of the Ancient text, the translation into Modern Greek, and the commentary have been done by Evangelos Spandagos. This work is published for the first time in Modern Greece. Its last edition was made in 1900 in Berlin.

"On Days and Nights" refers to the movements of the Earth around the Sun and the duration, due to these movements, of days and nights. The book is introduced by the astrophysicist (Doctor of the University of Athens) Vasileios Manimanis.