If you look closely you will see, just to the right of center, the thin line of the cable of Foucault's pendulum.
One of the guides led the group while the second one followed up, making sure no one was left behind. If I remember correctly, our group numbered about twenty or twenty-five. Each tour can accommodate a maximum of fifty people.
Looking down along the nave toward the choir.
The Panthéon offers six dome tours a day, two in the morning and four in the afternoon. I caught the 15h30 tour. That was the second to the last for the day. The whole thing took about forty-five minutes, start to finish.