The Domic Resonator is the first upgrade from you standard Fosic Resonator. This Domic Resonator can be used to show the range of rituals and other items by drawing a huge dome.
With the below Ritual pedestal it is impossible to see the range of the Ritual but using the Domic Resonator (right click the Pedestal) you will be given a visual guide:
This green dome is the range of the Ritual, the only way to remove this dome is to step out of it or to use the Domic Resonator on something else (like a Tree Beacon). This can be very useful when trying to see how far a ritual goes. This can also be used on the Tree Beacon.