Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The scholars stated that there are three differences between it (the false dawn) and the second (dawn):
1. The first dawn is vertical and not horizontal, i.e., i
t extends from east to west (across the arc of the sky) whereas the second dawn extends from north to south (across the horizon).
2. The first dawn turns dark, i.e.,
this light appears for a short while, then it goes dark, whereas the second dawn does not turn dark, rather it increases in light and grows brighter.
3.
The second dawn extends along the horizon with no darkness between it and the horizon, whereas the first dawn is separate from the horizon and there is darkness between it and the horizon.
Are any rulings connected to the first dawn?
No shar‘i rulings whatsoever are connected to it, such as stopping eating when you want to fast, or the time for Fajr prayer beginning.
The rulings are connected to the second dawn. End quote.
Al-Sharh al-Mumti‘, 2/107, 108
Secondly:
With regard to the available prayer timetables,
they are not a reliable source for finding out the time of Fajr prayer. The fact that these timetables are incorrect has been proven.
What you should do is not rely on the timetables to find out the time of Fajr prayer. You have to look for the correct time on the basis of what we have mentioned of the differences between the false dawn and the true dawn. If you cannot look at the sky every day, then you can delay it after the time mentioned in the timetable, to be on the safe side. In our country this time differs from one city to another and from one season to another. So you can delay it half an hour, for example, to pray Fajr, but to be on the safe side you should stop eating and drinking before that.
You can draw up a correct timetable to be used by those who come after you, after working out the time of the true dawn for a whole year, at various times. Perhaps you will attain the reward of correcting the Muslims’ acts of worship.
Based on that, if possible you can work out the time of Fajr yourselves and follow that in prayer and fasting. If that is not possible, then you should not pray until you think it most likely that the time for the prayer has begun.
With regard to fasting, you can eat or drink until you are certain that dawn has broken, because Allah, may He be exalted, says (interpretation of the meaning):
“and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)” [al-Baqarah 2:187].
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
So long as he is not certain that dawn has broken, he may eat even if he is not sure, until he is certain. End quote.
Fataawa al-Siyaam, p. 299
And Allah knows best.
Source