Can you see the curve of the Earth from the top of a tower? A New Scientist story.

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Fooled in Blackpoolhttp://www.newscientist.com/article.ns?id=mg19926742.900This interesting Article from New Scientist is for the Members Mental Excercise on whether you can see the curve of the Earth from the top of a tower? Pl. respond if the assumptions and conclusions are understood.

 

 

From the top of Blackpool Tower (approximately 150 metres) on the UK's west coast, can you see the curvature of Earth along the Irish Sea horizon? I thought I could, but my friend disagreed. If I'm wrong, how high would we have needed to be?

 

 

While camped at 6000 metres altitude in Peru in 1962, I and some colleagues asked ourselves this question about the Pacific horizon. We actually only saw the curvature by comparing the horizon (about 277 kilometres away) with a nylon thread stretched tight and level between two ice axes.

" We could see the curvature of the horizon when we stretched a thread between two ice axes "

While standing atop Blackpool Tower, if you sight the seaward horizon over a level, 1-metre straight edge, which is held 1 metre in front of you, trigonometry shows that the ideal horizon would appear to be almost a millimetre higher at the centre of the straight edge than at the ends. This is a much smaller effect than typical atmospheric distortion which, in effect, means there is no visible curvature.

From our camp in Peru, the difference was almost 6 millimetres - easily visible when compared with a straight edge. Even so, the curvature was not apparent when simply looking at the horizon.

Charles Sawyer, Byron Bay, New South Wales, Australia

As the radius of the Earth is 6373 kilometres, a little trigonometry tells us that if you are at the top of a tower of height h metres, the horizon will be at a distance of approximately (2 × 6373 × h)½ kilometres.

For a tower 150 metres high, the horizon will be 44 kilometres away and displaced downwards from a true horizontal line by about 0.39 degrees. If you hold a 1-metre stick horizontally 1 metre in front of you, seemingly touching the horizon at the midpoint of the stick, the ends will appear to be 0.8 millimetres above the horizon. That's pretty hard to see with the naked eye.

Eric Kvaalen, La Courneuve, France

When out in the mid-ocean, up at the top of the main mast, the horizon is a horizontal line right round the field of view. The higher the mast, the lower the horizon appears to be, but it is still a horizontal line.

John Eagle, Wilmslow, Cheshire, UK

The short answer to this question is that the curvature is not obviously visible from anywhere on the Earth's surface. Pilots of Lockheed U-2 and SR-71 Blackbird aircraft suggest that the Earth's curvature only becomes clear at an altitude of about 18 kilometres. Indeed, it has been photographed from Concorde cruising at this altitude. The curvature can be inferred at sea level, though. For example, ships disappear over the horizon from the bottom upwards, as if sinking into the sea.

Mike Follows, Willenhall, West Midlands, UK

From issue 2674 of New Scientist magazine, 17 September 2008, page 89-- Dr.V.N.Sharmahttp://canvas.nowpos.com/vnsharma

[Guest guest]



I have stood at the crest of a hill looking (7,000 feet) straight down to vast distances. A radar station is located at this hill for observing Pakistani aircraft deep in Paki airspace at very low altitudes. No curvature of earth was discernable although I looked for it, with and without spectacles. Such a phenomenon (curvature of earth) is not visible from aircraft flying at 30,000 feet or 10,000 metres.

 

Rajinder Sandhir

 

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Dr.V.N. Sharma

Thursday, September 18, 2008 10:59 PM

[HealthyIndia] Can you see the curve of the Earth from the top of a tower? A New Scientist story.

 

 

Fooled in Blackpoolhttp://www.newscientist.com/article.ns?id=mg19926742.900This interesting Article from New Scientist is for the Members Mental Excercise on whether you can see the curve of the Earth from the top of a tower? Pl. respond if the assumptions and conclusions are understood.

 

From the top of Blackpool Tower (approximately 150 metres) on the UK's west coast, can you see the curvature of Earth along the Irish Sea horizon? I thought I could, but my friend disagreed. If I'm wrong, how high would we have needed to be?