The word Ramadan is taken from the word ramad which is intensely or vehemently heated by the sun. And the word ramdhaa means the intense heat of the sun. "Do not fast unless you see the crescent (of Ramadan), and do not give up fasting (at the end of the month) till you see the crescent (of Shawwaal), but if the sky is overcast (and you cannot see it), then count Sha'baan as thirty days.” [Al-Bukhari and Muslim]