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If Triton had an equatorial orbit, then solar eclipses would occur around the Neptunian equinox - same as with Saturn and Uranus. But Triton's orbit is infamously inclined to Neptune's equator, so common intuition doesn't help in guessing when an eclipse will happen.

Googling this issue leads nowhere apart from articles on Triton occulting background stars. I'm pretty sure an easy way to see this would be to the set the location in Stellarium as the Sun itself, observe Triton, and note when it passes over Neptune. Unfortunately, I am unable to do so now or in the near future.

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According to Wikipedia, all of Neptune's inner moons can cause solar eclipses. At that distance, "the Sun's angular diameter is reduced to one and a quarter arcminutes across". Triton has an angular diameter of 26 to 28 arcminutes, so it can easily cover the Sun. However, Triton eclipses are quite rare, due to its highly inclined orbit. Also, these eclipses are very brief, because Triton's orbital period is only 5.876854 days (~5 days, 21 hours) and its orbit is retrograde relative to Neptune's axial rotation.

The Triton eclipse season occurs twice per Neptune's orbital period (164.8 years), and it's possible for Triton to eclipse the Sun several times during this period.

The most recent eclipse season occurred in late 1952 / early 1953. I think the closest eclipse occured on 1952-Nov-11 5:43 UTC. The next eclipse season will be in 2046, with the eclipses on 2046-Jul-30 15:39 and 2046-Aug-5 12:41 both being very close.

Here are some ecliptic latitude & longitude plots, produced using Horizons. The timestep is 10 minutes.

Neptune eclipse, 1952

Neptune eclipse, 2046


Here's a plot for (most of) a recent orbit of Triton, with a 6 hour timestep.

Current Triton orbit lat & lon

And here's the plotting script. The controls are similar to my 3D orbit plotting script given in this answer. Set the aspect_ratio to zero to use the default aspect ratio chosen by matplotlib. The offset option puts 0° longitude in the centre of the plot. The curve option will generally create a mess if the longitude wraps around.

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  • $\begingroup$ Thank you. I wonder if there's any scientific documentation from the 50's about this. $\endgroup$
    – user267545
    Dec 29, 2023 at 0:55
  • $\begingroup$ @user267545 I couldn't find anything in a brief search. I guess it would be very hard to observe from Earth, even with modern telescopes. $\endgroup$
    – PM 2Ring
    Dec 29, 2023 at 1:01
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    $\begingroup$ There's an improved version of the plotting script here: astronomy.stackexchange.com/a/55178/16685 (The old version can fail when a body has a complicated name). $\endgroup$
    – PM 2Ring
    Mar 27 at 10:29

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