THE LONG PERIOD EFFECT OF TWILIGHT ON THE ABILITY OFSEEING CRESCENT

Abstract

Twilight is a light which appears in the horizon before the sunrise and after the
sunset .This research is about the count of long period of twilight after the sunset for
a day born of crescent in Iraq for the city of Baghdad , Mousl , Basrah for many
years and for months of blessed Ramadan and Shawal . Studying the changes period
of astronomic twilight on the long of months of year for three cities . It is found that
the different between the bigger and smaller period for twilight on the long of
months of year arrives to (22 ) minute in Baghdad and in Mousl (25 ) minute , in
Basrah (19 ) minute . As well studying elements seeing crescent for this month .It is
found that there is a reflected relation between the long period of twilight and the
probability seeing crescent. When we take period of twilight (79 )minute , the
probability is (39.43% ) and it is less than the value of probability to see . There is a
reflected relation between the long period twilight and period of stay crescent. When
we take period twilight (79 ) minute , period stay crescent is (18.52 ) minute . It is
less than the value desired stay for seeing crescent as it showed the long period
twilight is certainly firm on the round seasons of year with a simple different . It has
not a huge effect on the probability of seeing crescent