First of all, thanks for making a very clear and concise video. It's a breath of fresh air around these parts. Here is my analysis using the Hilton Towers. I decided to use the Hilton Towers rather than the Skylon Tower because their proximity to each other allows us to get a good estimate of how much of the tower is visible.

**Round Earth Hypothesis:**Unfortunately, as User324 stated, you forgot to take into account the telescope's altitude. Based on the video, I am guessing you were about 3 meters above the lake. Assuming absolutely no refraction gives us

**253 m** obscured from 63 km away. From what I've read, a common way to estimate refraction is to increase the radius of the earth by 15% in our calculations. So assuming standard refraction,

**218 m** should be obscured.

**Flat Earth Hypothesis:**None of the building should be obscured, except what is blocked by other buildings.

**0 m** obscured.

**Observation:**Height of Hilton Tower 2 = 183 m

Elevation of base of tower = 205 m

Elevation of Lake Ontario = 75 m

I used

this website to find the elevations. This gives us a total height for Hilton Tower 2 above the lake of 313 m.

Hilton Tower 2 is 60 m taller than Hilton Tower 1. In your picture, Hilton Tower 2 is about twice as tall as Hilton Tower 1. Therefore, about 120 m of Hilton Tower 2 is visible.

313 m total - 120 m visible =

**193 m obscured****Conclusion:**Round Earth (no refraction): 253 m obscured

Round Earth (standard refraction): 218 m obscured

Flat Earth: 0 m obscured

Observation: 193 m obscured

None of them were perfectly correct. The Flat Earth hypothesis was obviously the most wrong. The Round Earth estimate with standard refraction was the closest (surprise, surprise). It was only off by 25 meters.

**Possible Sources of Error:**1. Height of observer was only a guess.

2. Actual amount of refraction was unknown. Local weather conditions are unknown.

3. Elevation data might not be 100% correct.