Machine translation of the Wikipedia article https://fr.wikipedia.org/wiki/Transit_d%27Uranus_depuis_Neptune to English by Google:
Imaging of a transit of Uranus from Neptune. (There will a priori be no transit on the date indicated, Stellarium , the software used, not being able to carry out calculations so distant in time.
The transit of Uranus from Neptune occurs when Uranus is directly between the Sun and Neptune . It then has, since Neptune, the shape of a small black disc moving slowly above the disc of the sun. This transit lasts approximately 42 hours.
This is the rarest transit among the eight planets in the solar system , given the long orbital period of 172 years (Uranus from Neptune), the tiny apparent diameter of the Sun (1.07 arc minutes, close to of the limit of human visual acuity ) as observed from Neptune, and the inclination of the two orbits relative to themselves, 1.5 degrees, which is smaller than that of the other groups of two planets.
Uranus' next transit from Neptune will take place in October 38172.
The transits observed from Pluto and other objects in the Kuiper belt and disc of scattered objects are even rarer, due to the inclination of its orbit, compared to that of other planets.
Notes and references
(en) This article is partially or entirely from the English Wikipedia article entitled "Transit of Uranus from Neptune" (see the list of authors).
(en) Jean Meeus , Transits , Willmann-Bell,1989
"SOLEX 9.1" [ archive ofApril 29, 2009], at http://chemistry.unina.it/ (accessed August 14, 2014)
Note that this French Wikipedia article says that it is "partially or entirely from the English Wikipedia article" and that page no longer exists!
I think the origin of this prediction is in question. Of course this transit can happen some time, but solar system modeling predictions this far into the future are extremely sensitive to even tiny errors in the present.
UPDATE: There is an entry in the Wikipedia article List of future astronomical events
- October, 38,172 AD A transit of Uranus from Neptune, the rarest of all planetary transits32
32Aldo Vitagliano (2011). "The Solex page". Università degli Studi di Napoli Federico II. Archived from the original on 29 April 2009. Retrieved 20 July 2012.
The archived page does not seem to contain a mention of this event, and the link to the original is dead.