Identify last time of Sahri and Fajr
The first dawn is the false dawn, which is whiteness that appears vertically in the sky like pillars. This happens approximately twenty minutes before the true dawn, and it increases and decreases according to the season.
False dawn is a temporary light on the eastern horizon that precedes the rising sun by about an hour; also called zodiacal light.Light that appears in the east just before dawn.
Some claims Persian Muslim astronomer Omar Khayyam (born 18 May 1048 AD,Neyshapur, Iran—1131 AD, Neyshapur, Iran) first discover it (http://www.youtube.com/watch?v=O8m_pmPTvgk) and some claims it was first investigated by astronomer Giovanni Domenico Cassini in 1683 and first explained by Nicolas Fatio de Duillier in 1684 (http://en.wikipedia.org/wiki/Zodiacal_light).
But long before Omar Khayyam/ Giovanni Domenico
Cassini/Nicolas Fatio de Duillier last prophet Muhammad (pbuh) (570 Mecca– June 8, 633 Medina),clearly stated about this matter al-fajr al-kaadhib (الفجر الكاذب) or false dawn.There are many ahaadeeth(sayings of Muhammad) which
speak about the two dawns, such as the following:
The Prophet SAWS (peace and blessings of Allaah be upon
him) said: “There are two dawns, the dawn when food becomes haraam and prayer becomes permissible, and the dawn when prayer (i.e., Fajr prayer) is haraam and
food is permitted.”
(Narrated by al-Haakim and al-Bayhaqi from the hadeeth of Ibn
‘Abbaas; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 4279).
And the Prophet (peace and blessings of Allaah be upon him)
said: “There are two dawns. With regard to the dawn which is like the tail of a wolf, this does not make it permissible to pray and haraam to eat. With regard to the dawn which appears horizontally in the sky, this makes it permissible to
pray and forbidden to eat.”
(Narrated by al-Haakim and al-Bayhaqi from the hadeeth of
Jaabir; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 4278)
According to another report, “There are two dawns. One is called the tail of the wolf, which is the false dawn that appears vertically, not horizontally. The other appears horizontally and not vertically.” (Classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, no. 2202).
Read more about fajr: http://www.al-islam.org/beliefs/practices/fajr.html
http://islamqa.com/en/ref/26763
