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--- un:almagest-revolutions [2025/03/02 00:26] – [2. From Arithmetic to Geometry] asad
+++ un:almagest-revolutions [2025/03/02 02:25] (current) – asad
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 In the work of transforming astronomy from mathematics to physics through cosmology, Galileo's name must be mentioned. Following the Dutch, Galileo made a telescope and first pointed it at the sky in 1610, seeing many unseen stars, mountains and valleys on the moon, the phases of Venus, and four satellites of Jupiter. By observing the phases of Venus, he understood that Venus indeed revolves around the sun, and Jupiter's satellites (observations from January 1610 are shown above) made him realize that it was possible for something other than the Earth to be orbited in the universe. Although not definitive proof, these two pieces of information made Galileo the greatest propagandist for Copernicus, for which he was sentenced to lifelong house arrest.
-By the time Newton published 'Mathematical Principles of Natural Philosophy' in 1687, there was little doubt among scientists and philosophers about the heliocentric model of 'Revolutions,' although it was not yet proven beyond all reasonable doubt. However, it is ironic that when Einstein published his modified gravity through the theory of general relativity, we somewhat returned to Ptolemy and Copernicus, to the Almagest and Revolutions. Because Einstein's relativity ultimately showed that there is no absolute motion; all motion ultimately depends on the coordinate system. To calculate the motion of the solar system, we can take any point as a reference, whether it is the Earth, the sun, or the center of mass of the entire system.
+By the time Newton published [[wp>Philosophiæ Naturalis Principia Mathematica|Principia]] in 1687, there was little doubt among scientists and philosophers about the heliocentric model of 'Revolutions,' although it was not yet proven beyond all reasonable doubt. However, it is ironic that when Einstein published his modified gravity through the theory of general relativity, we somewhat returned to Ptolemy and Copernicus, to the Almagest and Revolutions. Because Einstein's relativity ultimately showed that there is no absolute motion; all motion ultimately depends on the coordinate system. To calculate the motion of the solar system, we can take any point as a reference, whether it is the Earth, the sun, or the center of mass of the entire system.
 ===== - Proof of Revolutions =====
+==== - Aberration: 1720s ====
 To understand the first observational proof of the 'Revolutions' model, we need to go back to the eighteenth and nineteenth centuries from Einstein in the twentieth century. In the eighteenth century, the direct proof of Earth's motion around the sun came from measuring the aberration of light. The significant proof of the nineteenth century came from stellar parallax. The amount of aberration is about 20 arcseconds, while parallax is only 1 arcsecond. It took almost a hundred years for telescope precision to improve from 20 to 1 arcsecond, which is why the discovery of aberration (1720s) and parallax (1830s) are about a hundred years apart.
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 One of the greatest astronomers of the eighteenth century, England's James Bradley, published this change in the position of stars due to Earth's velocity in 1727. The observations of the aberration of Gamma Draconis (blue curve) and 35 Camelopardalis (red curve) are shown above. It is seen that the aberration of Gamma Draconis is at its maximum of 20 arcseconds in March and September. After Bradley's discovery, astronomers began to calculate the proper motion of stars by subtracting the effect of aberration caused by Earth's orbit from the star's position. This greatly increased the precision of observations.
+==== - Parallax: 1830s ====
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