✨In the 11th century, the famous Muslim polymath Al-Biruni figured out the Earth's radius using nothing more than a mountain and a bit of trigonometry. 📐
The insight was brilliant:
Stand on a mountain, and the horizon dips below the horizontal. That dip isn't an optical illusion; it's a geometric signal. It creates a right triangle where the mountain's height (h) and the Earth's radius (R) are the only variables.
Measuring the mountain's height without climbing down:
He used a simple trigonometric trick: from two points on the plain, he measured the angle to the peak. Knowing the distance between those points, he calculated the mountain's height with a formula surveyors still use today:
H = D / (cot A1 – cot A2)
From the peak, he measured the dip angle to the horizon: α = 34′ (just over half a degree):
R = h * cos(α) / (1 - cos(α))
How did he compute the cosine of such a tiny angle?
Without modern calculators, he used a sophisticated technique: he started with the known value of cos(60°) and used the half-angle formula to work his way down to the required value for his 34′ angle.
He calculated the Earth's radius as 6,340 km. The modern value is 6,371 km.
An error of less than 1%. In 1030 CE.
Three days after the abduction in Sitakunda, the packed Dead body of #Jubodol leader was recovered from Sea beach in Sayedpur, Sitakund.
https://t.co/IGnryakYYK
No words to describe the joy of speaking to @AungNaingSoeAns, released today from prison with his @trtworld colleagues after more than 2 months. He is relieved, grateful to all his supporters and described it as an experience. Now waiting for the same for Reuters colleagues.
We heard "#NeverAgain" after the Holocaust, it was said after Srebrenica, it was said after the Rwanda genocide, but it's happening right now, again. In #Myanmar. The #Rohingya#Muslims are facing genocide by the Myanmar army, and the word watches on. Again.
#HumanRights
#Myanmar to take back 450 #Hindu refugees from #Bangladesh at a refugee camp set up in #Rakhine as the first step of repatriation process https://t.co/jbm5ueKdZ0
According to the human rights org Odhikar, there were 408 disappearances recorded in Bangladesh between January 2009 and November 2017.
Most of them are opposition BNP, Jamaat & Shibir leaders and activists.
#BringBackOurBrothers#EnforcedDisappearances
Bangladesh army continues to be used for civilian law enforcement leading to allegations of serious human rights violations. Military intelligence, DGFI, accused in alleged disappearances. RAB a is force that deploys military into policing. https://t.co/KELvHKCwgp