09/24/2026
On this day (or rather, this night) in 1846, astronomers discovered Neptune!
After the planet Uranus was identified in 1781, observers soon noticed strange distortions in its orbit that didn't make sense according to Newtonian physics. However, they could potentially be caused by the gravitational pull of another, more distant planet not visible to the naked eye. By 1845, Uranus had nearly completed one full revolution around the sun since its discovery. Astronomers Urbain Jean-Joseph Le Verrier in Paris and John Couch Adams in Cambridge, England, both had the data they needed to independently calculate the location of this hypothetical planet in the night sky at a given time.
Based on Le Verrier's predictions, Johann Gottfried Galle was able to formally view the new planet from the Berlin Observatory on the night of September 23–24, 1846. It was only 1 degree from the calculated position! Subsequent investigation revealed that other astronomers had observed Neptune in the past, including Galileo more than two centuries before, but they had not identified it as a planet due to the relative slowness of its movement across the sky.
If you've read this far, there's a decent chance you're a huge astronomy nerd! If so, we think you'll enjoy the SMITHSONIAN ATLAS OF SPACE for the astrophysics, and ON A MISSION for the space program history🤩
https://www.smithsonianbooks.com/store/aviation-military-history/smithsonian-atlas-of-space-a-map-to-the-universe-from-the-big-bang-to-the-future/
https://www.smithsonianbooks.com/store/aviation-military-history/on-a-mission-the-smithsonian-history-of-us-women-astronauts/
Image credits: 1) NASA Voyager 2 post-encounter view of Neptune south pole as the spacecraft sped away on a southward trajectory, 5/8/1999. Courtesy of NASA/JPL. 2) Picture of Neptune produced from the last whole planet images taken through the green and orange filters on NASA's Voyager 2 narrow angle camera, 10/30/1998. Courtesy of NASA/JPL.
Source: https://www.nasa.gov/history/175-years-ago-astronomers-discover-neptune-the-eighth-planet/
