- commercial flight window seat on a clear day
- camera or phone
- optional straight-edge overlay when reviewing the image later
Experiment
Aircraft Horizon Dip Check
At cruising altitude, does the visible horizon sit measurably below true eye level?
Materials Needed
Setup Steps
- Take level-looking photos or short video clips of the horizon from a cruising aircraft.
- Keep the camera as steady as possible and avoid obvious fisheye distortion modes if you can.
- Compare the visible horizon with the cabin eye-line or with a later straight-edge overlay during review.
Expected Calculation
As observer height increases, the geometric horizon dips below eye level by a measurable angle. At aircraft altitude the effect is still modest, but it is no longer negligible.
Graphic
This visual shows the core geometry the experiment is testing before the real-world observation is made.
What to Observe
- The horizon usually sits slightly below the level line rather than exactly through it.
- The dip becomes easier to detect in stable frames with low distortion.
- The direction of the effect is consistent with higher-altitude curvature geometry.
Interpretation
A subtle but repeatable horizon dip at altitude matches globe geometry better than the claim that the horizon always rises exactly to eye level.
Sources
Evidence Card
Claim
At cruising altitude, does the visible horizon sit measurably below true eye level?
Model Used
Curved-surface hidden-height geometry checked against a field observation protocol.
Formula
As observer height increases, the geometric horizon dips below eye level by a measurable angle. At aircraft altitude the effect is still modest, but it is no longer negligible.Last Verified
2026-03-23
Assumptions
- Earth is treated as a sphere with mean radius 6371 km unless the linked tool applies refraction.
- Observer and target heights are geometric heights above the surface.
- Weather, mirage, and heat shimmer are treated as uncertainty bands, not as proof either way by themselves.
External Sources
A page-specific source set has not been attached yet.
What Would Falsify This Page
Repeatable shoreline or tower observations that matched flat-plane hidden-height predictions while violating spherical geometry under the same heights and distances would count against this page.