On this date in 1846, the planet Neptune was discovered by Urbain Le Verrier and John Couch Adams, then verified by Johann Galle. Galileo (the philosopher-mathematician-astronomer, not the spacecraft that orbited Jupiter) may actually have seen it more than two hundred years earlier, but he mistook it for a star. Additional controversy surrounded whether the Frenchman and the Brit should really share credit for the discovery, and recent assessment leans toward Le Verrier doing the more significant work.
Between 1930 and 2006, Pluto held the title of farthest planet from the Sun. Pluto was discovered by Clyde Tombough, who was born in Streator, Illinois, and later worked at the Lowell Observatory in Arizona. But Pluto was reclassified because it never cleared the neighborhood of its own orbit, and few were more devastated than the residents of Streator. In other words, it didn’t have enough planetary gravitas and doesn’t push and pull other objects in its orbital neighborhood. Neptune not only celebrates its discovery day today, but last week it celebrated the five-year anniversary of its return to ascendancy as the farthest planet from the Sun.
The eighth planet was named by its discoverer, Le Verrier, after the Roman god of the sea. The planet has thirteen moons. Neptune is seventeen times heavier than the Earth, has high surface gravity, and takes almost 165 years to orbit the Sun. None of us on Earth will live through a complete Neptune orbit. Imagine if each season lasted 40 years. What’s really mind-boggling when you think about time and how we measure it by the Earth’s rotation (a day) and orbit (a year) is that, because Neptune isn’t solid like the Earth, its equator takes about two hours longer to rotate than its poles, 18 hours and 16.1 hours, respectively.
Some of what we know about Neptune and many of the images we have of it—photos of its rings, its dark spots (storms)—are a result of the flyby of Voyager 2 in 1989. PBS based Neptune All Night on that spacecraft flyby. According to NASA, 11,000 workyears were devoted to Voyager 1 and 2 through the Neptune flyby; that’s equivalent to one-third of the work effort devoted to building the Great Pyramid at Giza. These spacecraft each carry a disc, the Golden Record, of 115 images and also many sounds, including greetings in 55 languages, chosen by Carl Sagan and his team, just in case Voyager runs into anybody else out there. Antennas are still tracking these spacecraft as they move farther and farther away, now into the Heliosheath. In fact, in 1998, Voyager 1 passed Pioneer 10 to become the spacecraft to travel farthest from Earth.
Okay, so maybe it’s not exactly the eight planet’s birthday, but discovery is worth celebrating. Unfortunately, Neptune can never be seen with the naked eye, but a telescope or even binoculars can help us make it out in the night sky. Click HERE for some information about peeking at Neptune this fall.
Lofty Ambitions Blog 
Great music, but Neptune is not the furthest planet from the Sun. Please do not take the controversial vote by four percent of the IAU, most of whom are not planetary scientists, as fact when this is not the case. Hundreds of planetary scientists rejected the “reclassification of Pluto in a formal petition led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. According to the geophysical planet definition, a planet is any non-self-luminous spheroidal body in orbit around a star (or that once orbited a star only to be subsequently ejected from that orbit). If the object is large enough for its own gravity to squeeze it into a round shape, it’s a planet. That makes Eris the furthest planet in our solar system though this may very well change with new discoveries.
Thanks for the comment! Here’s an account of the Pluto & Eris situation: http://www.astronomytoday.com/astronomy/eris.html. And here’s another with some cool info (we appreciate the title’s typographical remark): http://www.gps.caltech.edu/~mbrown/planetlila/.
I assume that you’ve seen this interview: http://www.thedailyshow.com/watch/wed-january-28-2009/neil-degrasse-tyson.
Thank you! I’ve been to pretty much all these sites, as I’ve spent the last five years researching the Pluto controversy. I’ve even gone back to school to study astronomy at least in part due to inspiration from the Pluto debate. You might even find some old comments on mine written in response to these articles. I am currently writing a book of my own on Pluto, so I’ve had to do a lot of research. Interestingly, Dr. Tyson seems to have moved to a more neutral position; in his TV program of “The Pluto Files,” he admits the debate remains ongoing.
Here are some sites for you to check out:
http://gpd.jhuapl.edu/ The Great Planet Debate, held at the Johns Hopkins University Applied Physics Lab in August 2008 in response to the IAU decision. I was lucky enough to attend and even give a brief presentation. Audio transcripts of all sessions are on the site.
http://laurelsplutoblog.blogspot.com My blog advocating a geophysical planet definition, just over five years old.
http://www.theatlantic.com/technology/archive/2010/12/the-argument-for-pluto-why-the-tiny-dwarf-is-still-a-planet/68123/ Previw of my Pluto book in “The Atlantic.” The book is still behind schedule.
http://www.nasa.gov/audience/foreducators/9-12/features/what-is-a-planet.html Exercise for high school students, “What Is A Planet?”
http://kencroswell.com/NinthRockFromTheSun.html Article by astronomer Dr. Ken Croswell on why Pluto is still a planet.
http://www.space.com/9594-fighting-pluto-planet-title-planetary-scientist-alan-stern.html Interview with Dr. Alan Stern, New Horizons Principal Investigator, on why Pluto and all dwarf planets are still planets.