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Comment by luc4sdreyer | Hacker News Reader

> Nobody had a clue

In the 3rd century BC, Aristarchus calculated that the Sun was between 18 and 20 times farther away from the Earth than the Moon, and proposed the Heliocentric model as a result. The true value is instead approximately 400 times. But it's incredible given that he didn't have lenses, the value of Pi, and that the Geocentric model was considered correct until 1800 years after his death.

https://en.wikipedia.org/wiki/Aristarchus_of_Samos#Distance_...

Nice video about the cosmic distance ladder by Terence Tao: https://www.youtube.com/watch?v=7ne0GArfeMs

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yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”.

He didn’t say nobody had a clue about heliocentrism.

But I believe he was the winner for many years under price is right rules.

Smugly: "1 mile."

Can you claim to be a winner under the rules of a game that won’t be invented yet for hundreds of years?

Yes. The fact that even this was a thought and he was charting the space bodies and trying to establish distances between them. The rules were invented. The players just were not famous.

* thousands

Plus they didn't know the distance to the moon

I appreciate that he worked on it at least. Around the same era, someone else calculated the circumference of the earth (and that it was round) in a pretty accurate fashion (between −2.4% and +0.8% off) based on measuring shadows on equally sized posts at different locations on the same date. Googled, it was Eratosthenes, the cities were Alexandria and Syene/Assuan.

One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: https://youtu.be/G8cbIWMv0rI?si=CuX49ki1GIvBLpeL

How did they take measurements in two different cities at the same time without clocks?

IIRC they walked directly north and measured at midday.

His method was fundamentally sound though. He realized that moonlight is reflected sunlight, and that if you observe the angle between the sun and the moon in the sky at exactly half moon, you can calculate the distance to the sun relative to the distance to the moon.

He almost certainly knew that it was closer to 400x, but could not believe it, or did not think others would believe it. Given the size of the Earth (which he knew), that would have made the distance to and the size of the Sun something hard to stomach.

Can we call it an estimation if it's a range (18 to 20 times further than the Moon) and yet it is incorrect?

If he said "between 2 and 1'000'000 times farther than Moon", it would be very imprecise, but not incorrect. If he said "20 times farther" - it would be an extremely inaccurate estimate.

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