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--- un:almagest-revolutions [2025/03/02 01:50] – [5. From Geometry to Physics] asad
+++ un:almagest-revolutions [2025/03/02 02:25] (current) – asad
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 ===== - 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 ====
 {{:courses:ast201:parallactic-ellipse.png?nolink&700|}}