How can a planet have a birthday?
In reality, it cannot. However we can celebrate its discovery in a way that is similar to the way we celebrate our own birthdays. Most of us celebrate a birthday each time our planet completes one orbit around the Sun. One Earth orbit of the Sun takes one year. Neptune was discovered by Johann Gottfried Galle, an astronomer at the Berlin Observatory, just after midnight on September 24, 1846. Neptune orbits the Sun at a distance more than 30 times farther than Earth. At that distance it moves slowly, taking nearly 165 Earth years to complete one orbit around the Sun.
July 12, 2011 marks one complete orbit for Neptune since its discovery. So happy “one-orbit-since-discovery-day” Neptune!