Is it obligatory for people to sight the Ramadan crescent?

A group of scholars held that undertaking to sight the Ramadan (definition) crescent is a communal obligation (fard kifaya); if all people neglect it, they are sinful. This is the view of the Hanafis, while some jurists contented themselves with stating that sighting the crescent is merely recommended.

The Hanafis made it a communal obligation to seek to sight the Ramadan crescent on the night of the thirtieth of Sha'ban. The Hanbalis recommended sighting the crescent as a precaution for fasting and to avoid disagreement. The Prophet, peace and blessings be upon him, encouraged seeking the sighting. Abu Hurayrah reported: "Fast when you see it (the crescent) and break your fast when you see it. If it is obscured from you, then complete the number of Sha'ban as thirty days." Aisha, may Allah be pleased with her, said: "The Prophet, peace and blessings be upon him, was more meticulous in Sha'ban than in any other month, then he would fast upon sighting the Ramadan crescent."

It appears that sighting the crescents of Ramadan, Shawwal, and Dhul-Hijjah is a communal obligation (fard kifaya) because two pillars of Islam are linked to it: fasting and Hajj.