Calculating radius of globe Earth using horizon drop @MathiasKp

Uploaded December 2018 | Updated September 2026, 1 week ago

A short video showing how to calculate the radius of a globe Earth using Al-Birunis method with angle of the horizon drop and observation height.

The measurements I use are taken from my other video: youtube.com/watch?v=6viR_GJ8998&t=340s

Results: https://flic.kr/p/PX2hUF

Al-Biruni: en.wikipedia.org/wiki/Al-Biruni
His method: owlcation.com/stem/How-to-Determin-the-Radius-of-the-Earth-Al-Birunis-Classic-Experiment

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$Why is the bottom part of Turning Torso behind water? Two hour timelapse of the view to Turning Torso over 21km, starts at 1:14 . No sign of varying refraction or mirages. Still the bottom part 22m is obscured by water, while observing from 0.8m. Air and water temperature, 2-3°C More weather data can be seen here, https://flic.kr/p/24MHUuK Camera position: http://www.google.com/maps/place/55.65236,12.64811 Height of Turning Torso, https://flic.kr/p/UHaPbQ Daylight photo, https://flic.kr/p/24LsFgM Night photo, 5sec, https://flic.kr/p/24LsEXv Night photo, 10sec, https://flic.kr/p/GtqNua #TurningTorsoFlatEarth$ $A ferry from Bornholmslinjen hiding behind the horizon, March 11th 2019 In this video I show how ships disappear bottom up behind the horizon. I didnt have a tripod with me so the footage is very unstable. Dandypanty made a stabilized version: https://www.youtube.com/watch?v=oVMxohidO40 The ferry is sailing between Rønne (Denmark) and Ystad (Sweden), https://www.marinetraffic.com/en/ais/home/centerx:14.4/centery:55.2/zoom:9 Ferry: https://www.marinetraffic.com/en/ais/details/ships/shipid:155510/mmsi:219017081/vessel:EXPRESS%201 On a different day (19th of March) I used an app to get the position of the ferry. I made a collage with all the needed data to calculate amount obstructed here https://flic.kr/p/2dVCxfR Ferry height estimated based on photographs: 24m Observer height: 4.05m Distance: 21.6km Amount hidden geometrical on globe Earth: 16.3m Amount hidden including std. refraction on globe Earth: 12.9m Amount hidden observed: ~13.3m$

$Turning Torso obstructed, no sign of compression or 4m tall waves Photo taken from 25km of distance and 3.7m of height. 1900mm telescope with SLR 1.53 crop factor - 2907mm Photographs: 2019:02:12 16:01:39, day https://flic.kr/p/SFZLay and with 3D https://flic.kr/p/2fP5whP 2019:02:12 17:31:44, day/night https://flic.kr/p/24dCS5v 2019:02:12 18:35:47, night https://flic.kr/p/24dCRjH Amount obscured matches a refraction coefficient k of ~0.12 Distance 25km Observer height: 3.85m Air/water temperature: 2-4°C Obscured observed: 21.3m Obscured on a globe Earth, geometrical: 25.42m Obscured on a globe Earth, geometrical with std. 7/6 refraction: 20.45m Height of Turning Torso: https://flic.kr/p/2f28vnT Observation point: https://www.google.dk/maps/@55.7138615,12.6207295,20z #TurninTorsoFlatEarth$

Mirage, 2h timelapse around sunrise of Turning Torso

Mathias Kp |

Calculating radius of globe Earth using horizon drop