Large numbers of Muslims converge once a year on Saudi Arabia to unite in a series of religious rituals and acts of worship as they perform the Hajj, the pilgrimage that is one of the pillars of Islam.

Adha, a period of "communal enjoyment" for Muslims worldwide, has officially arrived. Here's what we've learned about the Islamic holiday.

Eid al-Adha follows the completion of the annual holy pilgrimage. Eid al-Adha will be observed following the sighting of the moon during the evening of Friday, June 6 through Monday, June 9, according to the Islamic Relief organization.