The Mass is being offered in celebration of the anniversary of the pontificate of Pope Benedict XVI.
Here are some stills from that to give you a sense of the occasion.
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The vesting prayers
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One can see the basilica is filled to capacity
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The procession
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The prayers at the foot of the altar
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The incensation of the altar
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The subdeacon chants the epistle
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A very nice view of the original high altar of the basilica. The altar is covered by a wonderful ciborium.
The NLM hopes to provide you more photos from the official photographs that were no doubt taken for the Mass.