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Cosmic Distance Ladder on Instagram: "In the fourth century BCE, Eratosthenes took advantage of the small deviation between the angle of the summer solstice Sun in the cities of Syene (more or less on the Tropic of Cancer) and Alexandria (hundreds of miles to the north) to obtain the first reasonably accurate, recorded measurement of the circumference of the Earth. For this, he needed to know the precise distance between the two cities. We have joked that Eratosthenes hired a “graduate student” to walk between the towns. The truth may not be too far off—in that era there were professional bematists whose job was to precisely measure long distances, either through methodical pacing or with early odometers. The history of the cosmic distance ladder is replete with such carefully collected data which has always relied on two things: well-calibrated tools and a plethora of tireless researchers whose names have frequently been lost to history. We see this in the many scholars of Tycho Brahe’s Uraniborg collecting decades of heroic naked-eye astronomical observations. It is also in the adept organization and remarkable spectroscopic analysis of the glass plate photographs at the Harvard Observatory by dozens of the Harvard “Computers”—skilled women who developed the ability to categorize the spectra of hundreds of stars an hour and maintained a working knowledge of the features of thousands of bright stars in the northern and southern hemispheres. Today, teams of hundreds of scientists collect many terabytes of observational data streamed to us from a wide range of complex telescopes on Earth and delicately calibrated specialized instruments in space observatories. Eratosthenes would likely be baffled by the technology and sophisticated mathematics of modern astronomy, but perhaps he would recognize that it is still fundamentally the same type of science, driven by both data and theoretical reasoning, that it was in his day. He would certainly recognize the importance of the countless unsung researchers who wrangle the volumes of data that astronomy demands. #DistanceLadder #astronomy #bematist #DataScience #AncientAstronomy #RenaissanceAstronomy #HarvardObservatory #VeraCRubinObservatory"

3 likes, 0 comments - cosmic_distance_ladder on June 19, 2025: "In the fourth century BCE, Eratosthenes took advantage of the small deviation between the angle of the summer solstice Sun in the cities of Syene (more or less on the Tropic of Cancer) and Alexandria (hundreds of miles to the north) to obtain the first reasonably accurate, recorded measurement of the circumference of the Earth. For this, he needed to know the precise distance between the two cities. We have joked that Eratosthenes hired a “graduate student” to walk between the towns. The truth may not be too far off—in that era there were professional bematists whose job was to precisely measure long distances, either through methodical pacing or with early odometers. The history of the cosmic distance ladder is replete with such carefully collected data which has always relied on two things: well-calibrated tools and a plethora of tireless researchers whose names have frequently been lost to history. We see this in the many scholars of Tycho Brahe’s Uraniborg collecting decades of heroic naked-eye astronomical observations. It is also in the adept organization and remarkable spectroscopic analysis of the glass plate photographs at the Harvard Observatory by dozens of the Harvard “Computers”—skilled women who developed the ability to categorize the spectra of hundreds of stars an hour and maintained a working knowledge of the features of thousands of bright stars in the northern and southern hemispheres. Today, teams of hundreds of scientists collect many terabytes of observational data streamed to us from a wide range of complex telescopes on Earth and delicately calibrated specialized instruments in space observatories. Eratosthenes would likely be baffled by the technology and sophisticated mathematics of modern astronomy, but perhaps he would recognize that it is still fundamentally the same type of science, driven by both data and theoretical reasoning, that it was in his day. He would certainly recognize the importance of the countless unsung researchers who wrangle the volumes of data that astronomy demands. #DistanceLadder #astronomy #bematist #DataScience #AncientAstronomy #RenaissanceAstronomy #HarvardObservatory #VeraCRubinObservatory".

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