All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Muslims in
If the Muslims in a country are not able to know when the month of Ramadan starts in this case they have to follow the ruling of the nearest country to them for the beginning and end of fasting. They should not rely on the calculation of astronomers.
The one who migrates from one country to another during the month of Ramadan is obliged to follow the rules of the country to which he has migrated. Thus, he has to fast and end the fast with the community of the Muslims with whom he is living.
This is based on the saying of the Prophet said: "The beginning of fasting is when all of you fast, the ending of fasting is when all of you end the fasting and 'Eed Al-Adh-Haa is when you sacrifice your animals". [Abu Daawood]
Therefore, you should fast in
If it happens that you fasted less than twenty-nine days, then you have to make up for the day or days to complete the twenty-nine days of fasting, since the days of a lunar month can not be less than twenty-nine days.
Allaah Knows best.