The cathedral in Santiago say on their website the following about the Botafumeiro:
The Botafumeiro (“censer” in Galician) is one of the most famous and popular symbols of the Cathedral of Santiago de Compostela. It is a large thurible that hangs by means of a system of pulleys from the main dome of the Cathedral and swings toward the side naves. It takes eight men to move it, who are known as “tiraboleiros”. It weighs 53 kg and measures 1.50 metres; it hangs from a height of 20 metres and can pick up great speed.
The Botafumeiro is used for liturgical reasons, in the same way as a priest would use a censer at the altar. It operates during the Cathedral’s main solemnities during the entrance procession or at the end of the Eucharist. The purpose of this great censer is to symbolise the true attitude of the believer. In the same way that the smoke from the incense rises to the top of the temple’s naves, so must the prayers of the pilgrims rise to reach the heart of God. And in the same manner that the aroma of the incense perfumes the entire basilica, so must Christians, with their virtues and the testimony of their lives, impregnate with the good scent of Christ, the society that they live in.
— The Cathedral website
And when does it swing? The cathedral say that it will swing on the following days:
The Botafumeiro operates during the following Solemnities:
- The Epiphany: 6 January
- Resurrection Sunday
- The Apparition of the Apostle-Clavijo: 23 May
- The Martyrdom of Saint James: 25 July
- The Assumption of Mary: 15 August
- All Saints: 1 November
- Christ the King
- The Immaculate Conception: 8 December
- Christmas: 25 December
- Transfer of the remains of the Apostle: 30 December
In addition, groups can reserve the botafumeiro by contacting the cathedral at firstname.lastname@example.org
More on the cathedral website.