The Earth is not perfectly spherical. Its diameter is longer across the equator than between the poles; it is oblate spheroid. This fact is often questioned by flat-Earthers. According to them, every picture of the Earth from space shows the Earth as a perfect sphere, and never as an oblate spheroid. Then they would present it as ‘evidence’ that scientists have been lying to us.
But it is actually possible to determine that the Earth is in fact oblate spheroid from pictures of the Earth taken from space.
The Earth is spherical, but not perfectly a sphere. At a glance it would appear perfectly spherical. But let’s do precise measurements to pictures of the Earth taken from space.
We used satellite images from Himawari-8. The resolution of the pictures is 11000×11000, or 121 megapixel, which should be enough. For this purpose, we have to find images that show visible part of the Earth perfectly illuminated by the Sun. We could find 4 matching images as follows.
- hima820150923112000fd.png: 10906×10868
- hima820160320112000fd.png: 10905×10870
- hima820160923112000fd.png: 10906×10869
- hima820170922112000fd.png: 10906×10869
The number after the filenames are the size of the Earth in the corresponding images in pixels. The average size is 10905.75×10869. And the difference is 0.338%.
According to above measurements, we can actually determine that the Earth is in fact oblate spheroid. Its diameter across the equator is longer than between the poles. The number is also very close to the difference of the diameters in the WGS84 standard, which is 0.336%.
So, we can conclude that the pictures show the Earth as expected: it is an oblate spheroid, and the difference between its diameters is also very close to the expected number.
Detailed description of our analyses follows.
Finding Suitable Images
We need images that show the visible part of the Earth fully illuminated by the Sun, so we can easily measure horizontal and vertical distance in the images.
The Himawari-8 satellite is a geostationary satellite. It is always above the equator on a constant longitude. With that in mind, the images we need are taken when it is noon during equinox.
After perusing Himawari-8’s database, we could find four suitable images:
Unfortunately, during March 2017 equinox, Himawari-8 didn’t produce any image.
To perform analysis of the images, we used a shell script with ImageMagick. The goal is to perform the same processing to all images, and to avoid subjectivity. The following is the script we used.
#!/bin/sh for A in *.png ; do echo $A convert $A -fuzz 30% -trim +repage -format 'scale=5; %w ; %h; (%w / %h) - 1\n' info: | bc done
The script performs cropping, then it determines the dimensions of the results and calculates their difference.