Run a search of the planet Neptune and you'll find out all sorts of interesting facts. It's the fourth largest planet in the Solar System, its magnetic field is offset and does not go down a pole-to-pole line, and its moon Triton orbits opposite of Neptune's rotation — meaning it could not have formed in conjunction with the planet and must have been captured at a later date. 

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And speaking of dates, you'll discover that Neptune was discovered empirically by astronomer Johann Galle. Using disruptions in the orbital speed of Uranus that could only be caused be a very large body, Galle was able to narrow down where that "large body" should be and voila! Neptune joined the party on September 3, 1846.

Or not. 

Using the popular Starry Night computer software, David Jamieson of the University of Melbourne in Australia reversed-engineered the orbit of the planet by several hundreds of years back to 1612 to prove a long-held rumor. Cross referencing where Jupiter was at the time, Jamieson argues that it was no other than Galileo Galilei who should be credited as Neptune's formal discoverer.

By pure coincidence, Neptune and Jupiter were at nearly the exact same position in the sky when Galileo turned his telescope up. While the astronomer was busy identifying the Jovian moons Ganymede, Europa, and Calisto, he noticed a dim "star" to the upper left of Jupiter itself. A month later, Galileo examined Jupiter and its moons again, but the "star" had moved. It was now to the lower left. 

Galileo drew both scenes, and it is from these drawings Jamieson makes his case.

Had Galileo taken more frequent sightings, he would have seen Neptune pull off the very un-star-like stunt called planetary occultation. Because of the movements of Neptune, Jupiter, and the Earth itself, Neptune would have appeared to go backwards across the sky towards Jupiter from the left, get eclipsed by Jupiter, and then emerge again from the left. All astronomers of the age knew of occultation; Mars did it to Jupiter, Jupiter did it to Saturn, etc.

But Galileo had two things working against him. The first was that the idea of there being more planets other than the ones that could be seen with the naked eye was outlandish at best; in Galileo's time, Saturn was accepted as the most distant. That led to the second hurdle, that Galileo may simply not have recognized what he was seeing.

Jamieson is sure, as are other astro-historians, that Galileo would have figured it out...if only he had the time

Harried by the church for decades for his theories that the Sun was the center of the Solar System, and that, contrary to the Bible, the Earth did indeed move on its own, Galileo was famously brought to trial in 1633, forced to recant his ideas, and give up his work.

The drawing of Neptune was filed away, and the planet returned to the void until Galle, some 200 years later. 

TagsNeptune, Galileo, Jupiter