How does a ring laser detect Earth's rotation?

[journierman]

This is my first time posting here so I hope I am in the right place. So I have read about some scientists who have built a ring laser that is sensitive enought to detec the Earth's rotation. I can get how a ring laser can detect the rotation of a missile say if the laser path is perpendicular to the direction of the missile travel. I can not seem to get my head around how a ring laser could detect the rotation of the Earth if its sitting on the surface of the Earth and the beam path is not perpendicular to the Earth rotation. It seems like to me for a ring laser to detect the Earth rotation the laser path would have to go around the whole earth. Can anybody help me understand this?

 

[rumborak]

Wikipedia sequence: "Ring laser" -> "Ring laser gyroscope" -> "Sagnac effect"

https://en.m.wikipedia.org/wiki/Sagnac_effect

 

[Khashishi]

Why would it have to go around the Earth? If you take a rotating frame and move it off axis, it's still rotating by the same amount.

 

[journierman]

Sorry I am dense. So I understand how it detects rotation when you rotate the ring laser around the center of the area it encloses. I do not understand how it could detect rotation any other way. Does this help?

 

[rumborak]

Do you know the Coriolis effect? It's essentially that really.