OTL, Neptune was not recognised to be a planet until it was found to be perturbing Uranus' orbit in 1846, but it had been observed and noted on star charts before, first in December 1612 and January 1613 by Galileo Galilei. In July 2009, it was discovered that Galileo may have, in fact, recognised that what he took for a star had moved slightly. Unfortunately, Neptune had just begun its yearly period of retrograde motion across the sky, and consequently was nearly stationary against the background stars; as a result of this, he never looked for it again or realised that he'd found a new planet, presumably dismissing it as an optical aberration or atmospheric effect, or as a floater or other aberration inside his eyes.
But what if Galileo had happened to choose a different time of the year to observe that particular patch of sky? What if he'd seen Neptune while it was in strong prograde motion, and subsequently been interested enough to make more observations and chart the planet's track across the sky? What would be the effects of the eighth planet being discovered 233 years before OTL, and before planet #7 to boot? Would Neptune have shown observable (with the equipment of the time) discrepancies in its orbit that would lead to the rapid discovery of Uranus, or would the big gap between Saturn and the new blue planet have itself been enough to raise astronomers' suspicions and get them to look for the planet in between? Might the discovery of how vigilant one needs to be to keep from missing a planet, especially a slow-moving one like Neptune, itself lead to the earlier discovery of Uranus? Or might Uranus remain undiscovered until a century or two later, at which time astronomers wind up with egg on their faces trying to explain how they caught the dim, slow-moving planet far from Earth and the Sun, yet missed the bigger, brighter, faster, and closer planet? Would Neptune's much earlier discovery lead to astronomy progressing significantly faster than OTL in an attempt to find any more planets, pulling the other sciences along with it? Would it even be named Neptune ITTL? It might still have its OTL name, since it's still deep, deep blue, inevitably leading someone to thoughts of the sea, which inspired its OTL naming after the Roman sea god, and since there'll still be the precedent of naming planets after Roman gods, and combining the two leads one to the name of the Roman sea god, who just so happens to be called Neptune, but might the blueness instead lead some to think of the sky, of sweet, ripe, berries, or of their lover's eyes, and might the astronomers of the 1600s think "the Romans may have named the planets after their pagan gods, but we're Christians!" and name the newly discovered planet or two after prominent Christian figures, holy places, their home nations, or prominent political patrons instead? The possibilities are endless!
But what if Galileo had happened to choose a different time of the year to observe that particular patch of sky? What if he'd seen Neptune while it was in strong prograde motion, and subsequently been interested enough to make more observations and chart the planet's track across the sky? What would be the effects of the eighth planet being discovered 233 years before OTL, and before planet #7 to boot? Would Neptune have shown observable (with the equipment of the time) discrepancies in its orbit that would lead to the rapid discovery of Uranus, or would the big gap between Saturn and the new blue planet have itself been enough to raise astronomers' suspicions and get them to look for the planet in between? Might the discovery of how vigilant one needs to be to keep from missing a planet, especially a slow-moving one like Neptune, itself lead to the earlier discovery of Uranus? Or might Uranus remain undiscovered until a century or two later, at which time astronomers wind up with egg on their faces trying to explain how they caught the dim, slow-moving planet far from Earth and the Sun, yet missed the bigger, brighter, faster, and closer planet? Would Neptune's much earlier discovery lead to astronomy progressing significantly faster than OTL in an attempt to find any more planets, pulling the other sciences along with it? Would it even be named Neptune ITTL? It might still have its OTL name, since it's still deep, deep blue, inevitably leading someone to thoughts of the sea, which inspired its OTL naming after the Roman sea god, and since there'll still be the precedent of naming planets after Roman gods, and combining the two leads one to the name of the Roman sea god, who just so happens to be called Neptune, but might the blueness instead lead some to think of the sky, of sweet, ripe, berries, or of their lover's eyes, and might the astronomers of the 1600s think "the Romans may have named the planets after their pagan gods, but we're Christians!" and name the newly discovered planet or two after prominent Christian figures, holy places, their home nations, or prominent political patrons instead? The possibilities are endless!