If i happen to be at equatorial line, how do I know I am at zero degree latitude?
You may determine your geographic position with a GPS receiver. Good mobile phones contain such a receiver. See, e.g., https://www.androidcentral.com/how-does-gps-work-my-phone .
You can measure a zenith angle from your site to the Polar star. Knowing it's position at the Celestial Sphere (from astronomical catalogues) you can compute your latitude and decide how it is far from the equator. It will the astronomical latitude not the geodetic like used in GPS )))
If you are on the Equator, stars will rise vertically on the eastern horizon and set vertically at the western horizon. At any other latitude, they will rise and set at an angle to the horizon. (See an example in the image at http://cseligman.com/text/sky/equatorlarge.htm )
Geodetic equator is clear, but exists only in our mind.
Astronomical geodesy gives us only the celestial equatorial plane orientation on the celestial sphere, the points with zero astr.latitude don't form the plane itself due to plumb line deviations.
Also if one can't observe stars, the mean gravity on the equator should have minimum value (very approximate method to establish point most elongated from the axis of rotation)
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