# The Curvature of the Earth **URL:** \ **Category:** Factual Questions\ **Created:** [December 12, 2014, 11:58pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078 "2014-12-12T23:58:22Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![f.coli](https://avatars.discourse-cdn.com/v4/letter/f/eada6e/32.png) [@f.coli](https://boards.straightdope.com/u/f.coli)\ **Post date:** [December 12, 2014, 11:58pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/1 "2014-12-12T23:58:22Z")
While watching videos of Alan Eustace and Felix Baumgartner’s high altitude parachute jumps, the earth’s curvature looks obvious at that altitude, but I wondered if that may have been due to distortion of the lens. So, how high do you have to be to observe the curvature of the earth? I’ve only been on commercial flights, and it’s not obvious at 30,000 feet. But the two sky divers were over 130,000. Do the pilots of high altitude airplanes, like the U-2 or the SR-71, report seeing the earth’s curvature? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [December 13, 2014, 12:17am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/2 "2014-12-13T00:17:06Z")
Seeing the curvature of the earth is a gradual process as you go higher but it can become noticeable at 35,000 feet under perfect conditions if you have a wide field of view. Early high altitude test pilots like Chuck Yeager remarked on seeing it very obviously in very high altitude planes that they flew above 60,000 - 80,000+ feet. That is still much lower than many high altitude balloons that can go well over 120,000 feet. What you are seeing in the photos from the high altitude balloon really is the curvature of the earth rather than lens distortion. There are formulas to calculate how much curvature you can see at a given altitude but they are rather dry and this thread is about human perception so I won’t include those. The main point is that it is quite perceptible even at the level that some jets fly and especially business jets like a LearJet that cruise at over 50,000 feet. ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [December 13, 2014, 12:32am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/3 "2014-12-13T00:32:01Z")
First of all, the Earth is apparently still flat for [some people](http://en.wikipedia.org/wiki/Modern_flat_Earth_societies) [Here’s an entertaining Video](https://www.youtube.com/watch?v=Zb-cxF26ev0) it also mentions curvature of cos. However, since we got that out of the way, you can look [here stuff up about the horizon](http://en.wikipedia.org/wiki/Horizon) Here’s a [video](https://www.youtube.com/watch?v=4LPcNxYwhQo) telling you the formulas. Apparently you don’t need to be that high up at all, it’ just less obvious. [Here](https://www.youtube.com/watch?v=bco_p4V7-QU)you can see the curvature in action. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 13, 2014, 1:36am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/4 "2014-12-13T01:36:27Z")
At the upper end of airliner cruise, 43,000’, you can see it on a clear day. It’s subtle, but it’s there. It’s more obvious if you’ve got a wider field of view and no wing in the way. I’ve been to 50,000 feet a few times. Up there it’s unmistakable. It’s a gentle curve, but there’s no mistaking it for straight. The other thing is the coloration. Even in the low 40s you can really begin to see the gradations from darker blue above to lighter blue below. Over most of the US most days down in the 30s its so hazy you can’t \*sharply \*see the horizon, much less the colors or the curvature. And sharpness is really key to perceiving the curvature. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 13, 2014, 2:42am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/5 "2014-12-13T02:42:20Z")
> [@Shagnasty](#): > > … > There are formulas to calculate how much curvature you can see at a given altitude but they are rather dry and this thread is about human perception so I won’t include those. … Dry? _DRY_?! Not with **Doughbag** around. (Thanks, **Doughbag**.) ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 13, 2014, 2:53am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/6 "2014-12-13T02:53:24Z")
Under the right conditions, you can see this from rather low altitudes. I recall flying in a small plane north of Calgary on a day with superb visibility (easily 100 miles) and about 20% cover of cumulus clouds. The cloud bases were over 8000’, and we were flying at around 6500. Looking east, the clouds clearly curved down to the distant horizon - we were looking into the bottoms of clouds far away. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [December 13, 2014, 3:27am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/7 "2014-12-13T03:27:39Z")
> [@Xema](#): > > Under the right conditions, you can see this from rather low altitudes. > > I recall flying in a small plane north of Calgary on a day with superb visibility (easily 100 miles) and about 20% cover of cumulus clouds. The cloud bases were over 8000’, and we were flying at around 6500. Looking east, the clouds clearly curved down to the distant horizon - we were looking into the bottoms of clouds far away. I don’t think that’s what people normally mean when talking about seeing the curvature of the Earth though, that’s mich the same as seeing a ship disappear over the horizon. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 13, 2014, 3:43am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/8 "2014-12-13T03:43:50Z")
> [@Richard\_Pearse](#): > > I don’t think that’s what people normally mean when talking about seeing the curvature of the Earth though … Yes, in a strict sense I wasn’t seeing the curvature of the earth - I was seeing curvature of a layer of clouds several thousand feet above the earth. But curved it was. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [December 13, 2014, 3:55am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/9 "2014-12-13T03:55:32Z")
But you weren’t seeing a curved horizon which is what the OP is asking about. At what altitude would you notice that the horizon does not form a straight line? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 13, 2014, 4:54am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/10 "2014-12-13T04:54:38Z")
> [@Richard\_Pearse](#): > > But you weren’t seeing a curved horizon which is what the OP is asking about. Sorry, but I didn’t see where the OP specified a curved _horizon_. Still don’t. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [December 13, 2014, 5:55am UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/11 "2014-12-13T05:55:49Z")
> [@Xema](#): > > Sorry, but I didn’t see where the OP specified a curved _horizon_. > > Still don’t. It would be unreliable to use the clouds. The clouds might not be straight… you are assuming they were forming a reasonable straight edge, due to layers of air… Over that distance the layer might not remain at same height… clouds form at a front. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [December 13, 2014, 12:43pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/12 "2014-12-13T12:43:19Z")
> [@Xema](#): > > Sorry, but I didn’t see where the OP specified a curved _horizon_. > > Still don’t. It’s the only curvature of the Earth effect that varies with height so I thought it was obvious. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [December 13, 2014, 1:59pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/13 "2014-12-13T13:59:05Z")
Seems to me it’s pretty obvious from a typical commercial flight. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [December 13, 2014, 2:04pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/14 "2014-12-13T14:04:42Z")
> [@Xema](#): > > Sorry, but I didn’t see where the OP specified a curved _horizon_. > > Still don’t. When is a horizon not a horizon? When we look at the moon, we see it’s round: it has obvious curvature. What we’re looking at is the moon horizon, just from far away, where it’s only a bit smaller than a great circle. Of course, you can also see curvature in the moon by watching how the terminus changes shape as the moon goes through phases. No doubt you could do that on Earth too, at some height, but I’m guessing that’d be a bit higher than seeing the curvature of the horizon. Just a guess, though; I could be wrong. I don’t ever remember being able to see the terminus on Earth during a sunset or sunrise flight, but then again I don’t ever remember actually looking for it. Offhand, though, my guess is you have to be higher. My point here is that seeing curvature of the horizon IS seeing curvature of the Earth. Not the only kind of curvature observation you can make, but definitely one, and so it’s a perfectly legit answer to the OP even if the OP didn’t mean to limit the discussion to horizons. ---
**Author:** ![StrangerThanFiction](https://avatars.discourse-cdn.com/v4/letter/s/f05b48/32.png) [@StrangerThanFiction](https://boards.straightdope.com/u/StrangerThanFiction)\ **Post date:** [December 13, 2014, 2:24pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/15 "2014-12-13T14:24:54Z")
[![](https://i.imgur.com/eLa1jUW.jpg) ](https://i.imgur.com/eLa1jUW.jpg) This was taken from 47,000 feet. Some of the curvature may be due to lens distortion (iPhone 4 camera) but the sun silhouetting the horizon made it pretty apparent in person. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 13, 2014, 3:33pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/16 "2014-12-13T15:33:53Z")
> [@Isilder](#): > > … you are assuming they were forming a reasonable straight edge, due to layers of air… You’re right, I was assuming that - because I’d checked the weather and knew that cloudbase height was consistent over a very wide area. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 13, 2014, 3:38pm UTC](https://boards.straightdope.com/t/the-curvature-of-the-earth/707078/17 "2014-12-13T15:38:44Z")
> [@Learjeff](#): > > My point here is that seeing curvature of the horizon IS seeing curvature of the Earth. I certainly agree. > [@](#): > > Not the only kind of curvature observation you can make … Right - that’s kinda my point.