I decided to try to collect readily made, non-satellite observations which help confirm the roundness of the Earth. These are things you can go and actually see in the world around you which are either a direct consequence of the roundness of the earth, or a direct observation of it. I repeat myself: the things I’m listing here are things you can go and look at for yourself directly in the course of your life. As well, I know that flat earth believers have a few exhaustive lists containing sometimes hundreds of points that they suggest indicate a flat earth… I would note that repeating the same misconception eighty times in a row does not constitute a good point. As such, don’t expect me to write sixty points that say the same thing. Quantity doesn’t equal quality.

Moreover, understanding why these points imply roundness depends on both synthesis of the observations together and on use of Occam’s razor to suggest that imaginative flat earth alternatives are more complicated than necessary or would have unintended side-observations.

Time zone map from https://www.timeanddate.com/time/map/

1.) Time zones.

This one is an unavoidable first place observation that is profoundly hard to ignore. It’s so hard to ignore that flat-earthers turn back flips to try to add it to their models. This is why the U.S. is mostly awake at the time when China is mostly asleep. This is why that first day you travel to Europe for a vacation, you’re so completely screwed up: the sun is up, but your body is demanding that you sleep. How simple a thing, the sun rising at different times everywhere on Earth. The time of sunrise is delayed by traveling west and accelerated by traveling east; if you’re on an airliner crossing the pacific ocean, going west can prolong your daylight hours, giving you day light through a period which would otherwise contain both a day and a night, while going East reverses that, giving you a night of only a couple hours.

The reason it works is quite simple. The curve of the round Earth hides the sun from some locations and not others. If the Earth were flat, a sun that radiates in all directions equally would light the entire plane of the Earth at the same time because there would be no place on the surface hidden from it. That’s the problem with being flat: all of a flat surface is visible at once! The east-west delay of sunrise is due to the rotation axis of the planet; that axis is strung through the north pole to the south pole and the axis is nearly at right angles to the direction pointing to the sun. I do say “nearly” because the deviation of 23 degrees gives us seasons.

If you have not appreciated the effect of jet lag as a direct consequence of the roundness of the Earth, shame on you!

sun path in northern hemisphere
Image from https://sites.google.com/site/feutrill8/home/energy/passive-solar-house-design

2.) Seasonal variation of the daylight period.

In North America, why is daytime long in the summer, but short in the winter? It’s a consequence of the curvature of the Earth as associated with the tilt of the Earth’s rotation axis relative to the plane of the ecliptic!

When I said that the sun rises at different times everywhere on Earth, I did mean it. In addition to the time zones, there is a seasonal variation to the sunrise time as well which is linked to your latitude. The reason this point is important is because time zones are reproducible by a planet that is shaped like a cylinder… this isn’t flat, but it’s also not technically round. The north-south variation of the daylight period has to do with how your local reference measurement of “flat” varies on the surface of the Earth relative to how you travel around the rotation axis of the planet. To a good first approximation, there are only two days a year when everyone along a single longitude line has the same sunrise… the days of the equinoxes, which is to say the first day of spring and the first day of autumn. This occurs because the Earth reaches a place in its orbit where the 23 degree tilt of the rotation axis is in a direction that is exactly perpendicular to the direction toward the sun, canceling out the effect of the tilt on that day so that the north pole is neither leaning toward nor away from the sun.

You will note that this explains very clearly the track which the sun takes across the sky based on latitude. At far north latitudes, the sun never rises very high when it’s up and it takes a grazing path across the southern horizon before it sets. The opposite is true in the far south, where the sun takes a grazing path across the northern horizon. At other less extreme latitudes, the path of the sun can deviate either somewhat north or somewhat south of the apex of the sky; for example it always favors traveling south of that apex when seen from the United States or Europe, or north of it when seen from South Africa or Australia. At equinox, when seen from the equator, the sun rises dead in the east, goes straight overhead through the apex of the sky and sets dead in the west. At midsummer, in Iceland, the sun rolls around the horizon in a clockwise manner without ever quite setting. This is because the north part of the rotation axis of the Earth tips toward the sun during the summer just enough that no part of the local surface is obscured from sunlight throughout the day.

((edit 3-26-20: There’s a small detail here that I need to fix. On the day of the spring equinox, along the equator, the sun rises 23 degrees south of east, travels straight up to the apex of the sky at midday, then moves to set 23 degrees north of west. At the autumnal equinox, the opposite occurs, the sun rises 23 degrees north of east and sets 23 degrees south of west. Why does it do this? Because the axial tilt of the Earth is 23 degrees and this means that the belt of the Earth’s equator doesn’t lie in the celestial plane of the ecliptic. As such, during one half of the day, someone standing on the equator views the sun from below the plane of the ecliptic, then switches to seeing the sun from above the plane in the other half of the day, resulting in an inclination of the sun with respect to east and west at sunrise and sunset.

If you photograph a fixed portion of the sky containing the sun from the same position on the surface of the Earth at exactly the same time during the day throughout the year and then superpose all of those images, the sun will appear to trace out a figure called an Analemma. In this case, the analemma is shaped like a “Figure-8.”

Analemma photograph by Jack Fishburn taken 1998-1999 at Bell Labs in New Jersey. Credit Wikipedia.

For the inevitable flat earther who doesn’t understand, this photograph was taken in multiple exposures –yes, the buildings were front-lit so that you can see them! The exposures giving the sun’s position for the analemma were very very brief while the primary exposure used to brighten the buildings was with the sun at a completely different position in the sky off-camera. There is no fakery here; moreover, I invite you to reconstruct the circumstances and take an analemma photo for yourself in order to see the reality of it.

The analemma pattern is an elegant observation that depends quite strongly on the roundness of the Earth in large part because it is due explicitly to the rotation axis of the spherical body upon which we live.))

Flat earthers misinterpret the behavior of the sun during the day near the north pole region as evidence of a flat earth in large part because the behavior in that local region -only- is a close approximation of what a flat disc shaped planet, like a record turning around the Earth’s axis, can do during the day at the appropriate season. They then ignore the fact that mid-latitudes behave more like a turning cylinder and frequently omit that daylight in the extreme south behaves like a disc turning in the opposite direction from the north (if the sun is visible there.) Only a globe can tie all these local behaviors together. The fact that the sun disappears below the horizon in Iceland for months on end during winter is conveniently ignored by flat earth arguments… without a rounded curve to the Earth for the sun to hide behind, the sun would never be able to fall below any horizon.

The track the sun takes across the sky, and therefore the time it rises in the morning, relative to your latitude of observation throughout the year is best explained by a round Earth.

Image from https://www.moonconnection.com/moon_phases.phtml

3.) Common shape of observable celestial bodies.

Every planet or moon that you can look at through the telescope is always circular in shape when seen from every possible angle. It may be possible to argue that the moon is also a disc where the face is pointed toward the Earth and the disc is simply far enough away that it doesn’t deform when seen from different places on the Earth, but this ignores the hemispheric shadow patterns of the moon lit by the sun. Full moon always rises just as the sun sets; half moon is near its apex when the sun either rises or sets; new moon sets at nearly the same time as the sun sets. The shadowing of the half or quarter moon shows quite clearly that the moon has a spherical shape and that sunlight is obscured from some surfaces of the moon by the shape of the moon itself in a pattern that can only be spherical. All large planetary celestial bodies visible by an average telescope are apparently spherical by the same argument.

The argument that the Earth only has a disc-like shape in light of this is an argument of undue exclusivism. Why should the Earth, which is a body known to be bigger than the spherical Mars based on gravitational mass measurements, be a different shape than Mars, when it is known that all observable planet-sized masses are spherical in shape? Why should Earth be different? There are some tiny moons that have non-spherical shapes, but these are known to be much less massive than Earth. Truth is that nobody has ever looked through a telescope and seen even one (continuous) astronomical body with a flat, disc-like shape. (Galaxies don’t count because they are entirely discontinuous structures.)

lunar eclipse
Image from https://www.nydailynews.com/news/world/ny-news-super-moon-wolf-blood-lunar-eclipse-20190114-story.html

4.) The Earth’s shadow on the moon during a lunar eclipse is circular when seen at all inclinations.

When the Earth comes between the sun and the moon, a circular shadow can be seen to cut across the face of the moon, rendering the moon dark. The aspect of this shadow is always circular, no matter the inclination of the moon in the sky when it happens. If the moon sits near the horizon when it moves into the Earth’s shadow, the edge of the Earth’s shadow appears curved. If the moon is high up near the apex of the sky when it passes into the Earth’s shadow, the edge of the shadow appears to have the same curve. A disc would have a round shadow from one aspect, but differing curves from other aspects and at least one aspect where a shadow has a definite straight edge. The Earth casts no such shadow!

The shadow the Earth casts on the moon always has a rounded edge. This is only possible if the Earth has a globe-like shape which always projects shadows of circular aspect.

view from an airplane window
Image from https://www.photojaanic.com/blog/view-from-the-airplane-window

5.) When you’re standing on the ground, the horizon you see is sharp, with a clear edge between the sky and ground.

This is a subtle but very important point. Suppose you’re on a hike at the local open-space. You look off and marvel at the line of the horizon; the edge is quite sharp. If you try the same experiment in the window seat of an airplane (suppose you’re a deviant who unplugs from your personal screen during the airplane flight in order to actually look at the world around you for a moment) you would see that the horizon is no longer sharp. It becomes diffuse and very hard to see. Fact is that the horizon can only become sharpish again if you get up into space out of the atmosphere!

The distance to your local horizon on Earth depends on your altitude over the surface. The higher you go, the farther away you can look before the curve of the Earth hides what lies beyond. The only thing about this is that the atmosphere is imperfectly transparent; over a distance of miles, particulates in the air and heat fluctuations tend to scramble up the straight lines that light rays would prefer to travel. As such, the further your horizon is from you as long as there is intervening atmosphere, the harder it is to see clearly. This variation of horizon clarity as a function of your altitude when you try to see it is a direct consequence of the roundness of the Earth and you can observe it yourself by comparing how the horizon looks depending on if you’re standing on the ground or if you’re in an airplane. The sharpest horizon will always be the one encountered at the lowest observation altitude.

Now, this shows an important effect of flat earth that’s rarely ever discussed. If the Earth is flat, the horizon line while standing on the surface is expanded to being the distance of the edge of the surface, which is as far away as the edge can possibly be. The path light must travel to bring an image of that distant edge is through a huge amount of atmosphere (even flat earthers would have a hard time denying the existence of the very air they breathe). This means that images of the horizon line would be very scrambled up and difficult to see. So, on a flat earth, the surface of the Earth would merge smoothly with the sky and you would likely not really see a line dividing them. Note, you would need to be away from obstructions like mountains and hills to see this… you would need to be on a flat with an unobstructed view of the “horizon.”

curve of the earth 2
Image from https://www.nasa.gov/feature/top-15-earth-images-of-2015


6.) You can actually see the curve of the Earth if you know where to look for it.

Given the example of the above image, we’re all sort of conditioned to think that the Earth can never actually look curved while standing on the surface. When the horizon is very close, it’s true: the curve is very slight and difficult to see. There is however a conditional way in which you can start to see some things you may not have expected. If you use a true straight edge to compare with what your eyes might otherwise think to be flat, you will find curves… for instance, looking at the surface of the ocean with a straight edge in hand. Here, you might suddenly realize that the ocean can be drawn up into a bulge over a distance of miles, perhaps due to pressure shifts or the vagaries of the tide. More even than that, if you do this experiment at the top of a sky scraper, say the Empire State Building in New York looking east, the deviation predicted by the actual curvature of the Earth relative to the sight horizon is appreciable enough to be visible on comparison to a straight edge (as in, ~2 millimeters of gap at either end of a ruler held in front of your face). Sitting in the pilot seat of an airliner or a jet fighter at cruising altitude with a full appreciable view of the horizon, the curve should be qualitatively visible even if the horizon line is very diffuse in the distance.

I started doing calculations about this after I noticed a curve to the ocean surface while I was standing on the sea shore. I was trying to determine how visible the curve of the earth actually is and it turns out that it is visible to an unexpected degree at relatively low altitudes if you have a good straight edge to compare it to. As I said, you can absolutely see it from a skyscraper if you use the correct tools to look.

Edit 9-24-19:

When I started doing calculations on this, I also started to look for it deliberately myself. I particularly tried to look out of the window whenever I got to fly in airliners, but I failed most of the time because the clarity of the horizon is just very bad without absolutely perfect conditions. Recently, I got lucky and managed one flight where I had perfect conditions.

Look closely at the following picture and tell me what you see:


Looks pretty flat there, doesn’t it? In this particular case, I got very clear skies with low lying clouds marking exactly where the horizon is. There are some scattering effects to the light which make the horizon very difficult to see, which is to be expected at this altitude in an airplane (note the previous point); I tried this experiment both with and without clouds and the clouds here only serve to make the effect more visible. This picture was taken with a plain old Samsung Galaxy S8 pressed up against the window. No special filters, not fish eye lenses. To the unaided eye, you may not see it, but check out what happens when you add a computer perfect straight edge for comparison:

formatted curve picture

The horizontal red line was applied to the picture in Power Point and shifted downward until it grazes the horizon in the center of the picture. If you then follow the rim of the horizon to the edge of the picture, you’ll note that there’s a gap between the red line and the horizon! The gap is marked here with the small yellow bracket on the right edge. On the opposite side, near the airplane wing, the red line is also above the horizon, showing the horizon to be a distinct convex curve. This, folks, is the curve of the Earth seen from the window of an airliner at cruising altitude!

If you doubt me, I beg you, go and do the same experiment. Look for yourself! It isn’t hard. Further, this is really a tiny picture… when you see it with your eyes, you’ll note that it’s easier to see because of the actual large size of the sky! That it appears in this picture is a testament to how visible it actually is.

For the inevitable fool who claims that the window of the airliner contains a fish eye, look at the wing of the airplane. It’s straight, or maybe even bent in the wrong direction to suggest a fish-eye. Some of these windows do bulge and deform, but you can shift your head around and see for yourself where it does, then look out of a region of the window that minimizes this distortion. The problem with random fish-eye lens claims usually comes down to the pesky fact that foreground features in the picture have straight edges, which wouldn’t happen with a true fish-eye. Moreover, you could always go to the open air observation deck of the Empire State Building and look for the curve from there… no windows to block you then!

Image from https://www.mnn.com/earth-matters/climate-weather/stories/nasa-images-of-hurricanes-from-space

7.) Cyclonic motion of hurricane-type storms is due to the roundness of the Earth.

Why is it called a cyclone? Because it has a distinct cyclic motion… it turns in a circle!

A cyclone north of the equator turns in a counter clockwise fashion when seen from above. A cyclone south of the equator turns clockwise. This always occurs. Why?

The typical party line of what causes this is simply the “Coriolis effect,” which is absolutely true. The reason Coriolis effect occurs is because of the slight decoupling between the atmosphere and surface of the planet on the large scale of the storm. When examined in the northern hemisphere, as the Earth rotates (in a right-hand sense going from West to East as seen from space) at the southern edge of the storm, the surface of the Earth is traveling slightly faster to the East than at the northern edge. As a result, the surface of the Earth drags the southern edge of the storm just a bit more strongly than the northern edge. The established fluid mechanics that hold the storm together reflect this by creating a gyre that goes fast to the East along the south edge, circulates to the north, swings around back south, and is accelerated again to the East at the southern edge where the surface drags on it most strongly. Many people misunderstand that Coriolis Effect is the same thing as Coriolis force, which it actually isn’t quite. The reason for the difference is because a basic assumption of the pure Coriolis force is that objects experiencing Coriolis force are completely decoupled from the rotating frame when they are moving, which is actually not true on real Earth where the atmosphere is only loosely decoupled from the surface… a rotating storm rotates because it can’t feel the full Coriolis force since the atmosphere isn’t moving totally decoupled from the surface. You could almost say that the highest altitude part of the storm is feeling the fullest Coriolis force, while the lowest altitude part is being sheared from the top of the storm by its coupling to the surface.

The reason flat Earth models can’t handle Coriolis effect is because the flat Earth can’t reverse the direction of storm circulation when observed south of the equator. In the southern hemisphere, the northern edge of the storm is dragged most strongly to the East, causing clockwise circulation by the same mechanism I outlined above.

How do you observe all this without a satellite photo? This would be fairly subtle because you need to know where you are on the surface in relation to the center of the storm, to know which direction the wind should be expected to travel. In other words, it would take some dedicated thought and careful observation, which flat earthers don’t seem to do that well!

As a small aside, the direction that water circulates as it goes down the toilet or is let out of the sink is actually not a reflection of Coriolis effect, regardless of the popularity of the claim. You can establish circulation in either direction under these circumstances because the coupling of the water to the surface here is very strong and there are only tiny differential forces on the water across the diameter of your toilet bowl, so effects of local water flow tend to dominate over effects of the rotating Earth.

Image from https://www.constellation-guide.com/the-southern-cross/

8.) Certain constellations are visible in the night sky only from certain places on Earth because the horizon of the round Earth otherwise hides them.

The constellations of the zodiac are only visible for half a year. Not the same half a year for each sign, to be sure, but only half a year at a time. Why is this? Because the period of time that we mark as a day is totally decoupled from the period of time that it takes for the planet to go around the sun. A year takes 365.25 something or other days (New Years Eve is the most arbitrary and ridiculous holiday ever… the Earth basically never actually finishes its orbit around the sun when the Ball drops in Times Square). For half of the Earth’s orbit around the sun, the body of the Earth points you toward the sun when certain zodiac constellations would be up in the sky, washing them out. Those constellations then rise at night for the other half of the Earth’s orbit, visible when the sun is no longer in the way. Literally, the body of the Earth blocks you from seeing certain things at certain times, but not at other times. This in itself could be explicable on a flat Earth, except for the next part.

For certain constellations, depending on whether they are in the far northern part of the sky or the far southern part of the sky, are never visible from certain locations on the surface of the Earth. The north star, Polaris, is not visible from south of the equator. The Southern Cross, on the other hand, is not visible from north of the equator. When you’re at the north (or south) of the planet, the body of the planet blocks constellations in the south (or north) part of the sky. Traveling smoothly from North to South and seeing certain constellations become visible above the local horizon is a direct result of the Earth having curvature.

walsenburg spanish peaks
Image from http://one-pilgrims-journey.blogspot.com/2016/01/walsenburg-spanish-peaks-in-colorado.html

9.) During travel on the surface of the Earth, you can see big mountains rise up over the horizon as you approach them.

I’ve included this point because it’s true. I’ve also specialized this argument to suggest a mode of observation. Leave the telephoto lens at home. Just watch for it as you drive across the prairie toward a big mountain range.

This is the old “mast of a ship disappearing over the horizon” argument. The one big problem with this argument is that it depends on you making the observation in such a way that you don’t pick up the non- linearities possible in the travel of light. For the region of sky very near to the horizon, light grazing along the planet’s surface has a maximal probability of interacting with abrupt shifts of density in the air caused by local coupling of the atmosphere to the ground (say by heat radiating off the surface, or cold water sucking heat out of the air). Within these regions, light rays can be uniformly bent so that images of the sky are projected apparently into the ground or images of the ground are projected up into the sky. With a telephoto lens, you can see these images, which may be originating from somewhere beyond the local horizon. This is of course part of why the horizon line becomes increasingly hard to see when examining it from high over the surface as mentioned before; light doesn’t always travel in straight lines and the longer the light interacts with the atmosphere, the more likely it is to bend in some unpredictable fashion.

Looking for mountains coming up over the horizon can get the view you’re looking for up above this cluttered region where the light does weird things. (Keep in mind that Flat Earthers use weird optical effects as an argument for the flatness of the Earth).

Image from https://en.wikipedia.org/wiki/Fata_Morgana_(mirage)

I’m concluding here with an example of a Fata Morgana –the cool name for a type of mirage. In this kind of mirage, the surface of the ocean is hotter than the air above it, meaning that the accompanying density change through the volume of the air places high density air above low density air. The shift in the index of refraction allows certain rays of light at very shallow angles of incidence to experience “total internal reflection,” where the air can act as a mirror. There are a great many photoshopped fake Fata Morgana pictures showing boats hovering above the water. To be a true Fata Morgana, the image will include both the actual boat, seen directly and, beneath it, it’s reflection off the density-shift mirror formed in the air over the water, making it look like twin boats joined at the bottom. You can see Fata Morgana type mirages for yourself on a hot day driving down a long, flat, empty road. It’s simply an image of the region of sky just above the horizon. What this mirage proves is simply that you must always be careful with your eyes. Some things you think you see are true, while some are false. I’ve listed a series of true observations above, pending an extraordinary reinterpretation that I know (from satellite data) not to be forthcoming.

I may or may not add to this list as I encounter other unique, observable points.

Published by foolish physicist

Low level academic enthralled with learning how things work.

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