On July 12, 2011, we celebrated what some have called “Neptune’s birthday.” Hubble released four pictures of the planet to commemorate Neptune’s first full orbit since its discovery on September 23, 1846. On that day, Johann Galle at the Berlin Observatory found Neptune based on the mathematical prediction of a French astronomer, Urbain Le Verrier. Because Neptune takes almost 165 years to complete its orbit around the Sun, a lot has happened during the Neptunian year since we learned of the planet’s existence.
However, calling this a “birthday” smacks of anthropomorphism and a human-centered view of the universe. Neptune has been around for billions of years, and no one can say when it was “born” to any precision better than many millions of years. In the grand scheme of things, does it really matter that we finally got around to noticing Neptune on that day? Plus, it is fun to note that Neptune had been seen before that day, but not recognized for the planet it is.
A few months earlier, in England, James Challis was actually searching for the new planet, based on the prediction of John Couch Adams, not Le Verrier. After the discovery was announced, it was uncovered that Challis had observed Neptune twice, but had not analyzed the data enough to find it. The national rivalries were strong in those days, and so was the outcry that England had “lost” the discovery to France and Germany. The full story of Neptune’s discovery makes for one of the best scientific soap operas of all time (try to find the out-of-print book “The Discovery of Neptune” by Morton Grosser).
Going back further, the earliest observations of Neptune date back to some of the earliest observations with a telescope. In December 1612 and January 1613, Galileo was following the motions of Jupiter and its four large moons, which he had discovered a couple years earlier. Neptune was in his field of study, and was noted by Galileo as seeming to move relative to a nearby star, yet not recognized as a planet.
All in all, anytime is a good time to release more Hubble pictures of Neptune. Since its the seasons last over 41 years each, we’re getting a drawn-out and detailed view of the emergence of summertime in Neptune’s southern hemisphere.