1. Rabbeinu Tam's opinion of 72 (or even 96 minutes) for night after the

setting of the sun contradicts known facts. Obviously half an hour

after sunset in the springtime in Jerusalem the entire sky is quite dark

with numerous stars. It is well known that the "bein hashamosot" is much

shorter in Jerusalem (or babylonia) than in northern Europe.

The Gra in Shulcahn Arukh notes that the time between dawn and sunrise

differs much from the time betwwen between sunset and stars. However,

he doesn't seem to be bothered by the little time it takes 3 stars

even small stars to appear.

Kol Tuv,

Eli Turkel