Ulugh Beg
Ulugh Beg determined the length of the tropical year as 365d 5h 49m 15s, which has an error of +25s, making it more accurate than Nicolaus Copernicus' estimate which had an error of +30s. Ulugh Beg also determined the Earth's axial tilt as 23;30,17 degrees in sexagesimal notation, which in decimal notation converts to 23.5047 degrees.