nikhil.io

Enjoyed this two-part video titled “How We Measure The Cosmos” by 3Blue1Brown where ace mathematician Terry Tao explains how human beings answered the question “How far away is that thing?” over our history and at a cosmic scale. Took us a good while and, as one could predict, got faster towards the current time. Trying to answer that question also led us to discover (and only around 100 years ago!¹) that our galaxy is merely one of 100-200 billion in the observable universe².

In that video, Prof. Tao talks about how you can infer the shape of the Earth based on the shadow it casts on the moon. Some searching led me to this amazing image. This is not what happens in the sky, however. You’ll need to imagine a fern frond³ unfurling to form a nice long arc when you meditate over it:

1. Well ahkchually they spotted one in 1845 but didn’t know it was outside our own galaxy so I’ll stand by my exclamation.↩︎

2. “The numbers are not going to change much,” Livio added, pointing out the first galaxies probably formed not too long before that. “So a number like 200 billion [galaxies] is probably it for our observable universe.”↩︎

3. Which are known as ‘fiddleheads’ for a reason that took me longer than permissible to understand…↩︎