The Aetherscope is a device that allows you to see spirits from "the other side", having a prominent role throughout the Easter Egg quest. It can be built on the crafting table under the Cyclotron, and requires three parts.
Only one part spawns at a time, and the order is random. So you have to locate a part on one of the three locations before you can find the next part at another location. The three locations are all in the Dark Aether, so you have to travel through the dimensional anomality again.
Location 1: In the Cyclotron room, at the staircase leading towards the upgrade station, right next to an Aether Tunnel and a vent.
Location 2: In the Spawn Room, outside next to the blocked staircase.
Location 3: On top of the engine of the crashed plane.
After having built and picked up the Aetherscope, it will work for all teammates. The device detects anomalies in the Dark Aether, like spirits and special objects.