Researchers include biologists, geologists, oceanographers, physicists, astronomers, glaciologists, and meteorologists. Aerial telescopes were employed by several other astronomers. The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists. The King was a proficient amateur astronomer, who collaborated with the best French astronomers. The observatory was destroyed and dozens of talented astronomers and mathematicians were driven away. Aryabhata and Varahamihira were two great astronomers and mathematicians. Each crown appointed three astronomers and cartographers, three pilots and three mathematicians. The Planet Nine hypothesis is supported by several astronomers and academics. Astrophotography is a popular hobby among photographers and amateur astronomers. They have several notable advantages for amateur astronomers intent on research. The sundial was further developed by Muslim astronomers. Proper motion was unknown to ancient astronomers. However, it also corrected Ptolemy based on findings of earlier Arab astronomers. The effect is well-known among amateur astronomers. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership.