Ask HN: Is there a globe with the exact shape of the Earth? | Hacker News Reader

Ask HN: Is there a globe with the exact shape of the Earth?

12 pointssoneca15 comments

Is it possible to buy a globe that models with reasonable accuracy Earth's topographic surface? Not a sphere, nor the oblate spheroid approximation, but the real thing?

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To scale? It's about 1000-to-1 ratio from Earth's diameter to the tallest mountains. A 1 m globe would have 1 mm tall mountains.

I saw a video on YT that said basically if you scale the Earth down to something you can place on a table, it would still feel smooth to the touch. The globe would have to be some really huge number before you could detect features by touch.

Unfortunately I don't remember what channel that was. But they did a lot of comparisons to show why. You can pretty much get that idea just looking out a jet window, since the Earth already looks pretty smooth even at that close range.

While everyone else had mentioned that Mt Everest would barely be a blip when making a round globe, I want to bring up another way the Earth is non-uniform as a sphere: The elipsoid shape, in that Earth is wider around the equator than it is on a north-south axis[1]. That's attributed to the rotation of the earth, and it's about 70,000 feet - Or about 11 miles. Out of a diameter of 8000 miles, I don't think you'd be able to spot the difference in the same 1 meter sphere that people are holding as an example.

It'd make a very cool art project, though.

https://oceanservice.noaa.gov/facts/earth-round.html

The most oblate planet is Jupiter. Being large, rotating rapidly, and being kind of squishy[1]... it's about 6% wider than it is tall, which is around 9,000 kilometers. Enough to be noticeable to the eye.

[1] Ok, squishiness doesn't really factor into it.

Are you looking at the specific mountain range shapes too, or simply the overall gist of the ball-like part?

I wonder if it could be 3D printed with reasonable precision to suit your needs. I'd look at shapeways, and if you can't find it maybe somebody can 3D model it for you first.

https://www.shapeways.com/marketplace?tag=earth

Both. The overall shape and the mountains and ocean deeps.

From your link, there is this "Topographic model" (https://www.shapeways.com/product/Z4BFMJN63/topographic-eart...), which is close, but it still seems to assume a perfectly spherical overall shape (which I think it is incorrect).

How are you going to perceive the .01% difference in height vs width of the earth? Are you planning to use calipers to study it?

I assumed the difference was more than that. So apparently the premise of my question was wrong. The topographic model seems to be enough for what I want

Generally when you say those very lumpy models of the Earth, they've exaggerated elevation differences by many multiples. On Wikipedia there's an image with elevation exaggerated 10,000x: https://en.wikipedia.org/wiki/Geoid

How do you define "exact"? What are you measuring?

I am thinking of a scale of how Earth is shaped (without the water).

"Exact" was used in opposition to the commonly used perfect spheric models you can easily buy. I am not sure how precise you want me to define "exact", though; I used it unpretentiously.

The challenge is that when the Earth gets shrunken down to the size of a globe the height differences of the topographical features become imperceptible. The same is true for how oblate the Earth is at the equator, its too subtle to appear at-scale. I don't have the math but I believe the height difference between Mt.Everest and the Mariana Trench is thinner than a sheet of paper for the size of globe that can fit on your desk, if I recall correctly.

Right. The height difference between the high and low points is roughly 20 km. That's 1/650 of Earth's diameter of roughly 13000 km. If your globe on your desk is 65 cm wide, the topographic variation is 1 mm. Not quite thinner than a sheet of paper, but imperceptible to the human eye.

Globes that show topography magnify it in the vertical direction, by at least 10x. Mountains may look huge to us puny humans, but they're infinitesimal at the scale of Earth's full size.

Thanks for both clarifications. I should have done the math before asking.

If you would’ve done the math first I wouldn’t have enjoyed the conversation. Now we know. I actually had a globe back in the day that did have raised areas for land. That was obviously not to scale. Now you have to figure out how to explain to flat earther’s their big question “how does the water stick?”. I suppose if you figure out how to shove enough mass into that globe, you could show them how gravity would do it. ;-)

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