Can Pluto be seen with the naked eye from Neptune when Pluto and Neptune are closest?

  • When Neptune and Pluto are closest, about 100 million mi (160 million km) from each other, would an observer on Neptune (or rather on one of its moons, since Neptune is gaseous) be able to see Pluto, and maybe even Charon, with the naked eye? If not, could Pluto be seen in average binoculars? I think Pluto would appear a bit smaller than Mercury from Earth (but at much lower apparent brightness because of the distance from the Sun).


    Hi, this is not an answer to your question, just an idea. If you have Stellarium, you could change the planet in location window to Neptune and watch Pluto from there. It gives you an endless opportunity to tweak and try things. All the best!

    @lordparthurnaax Thank you. I do have Stellarium, but I dunno when Neptune and Pluto came/come closest. I think it was in the 1970s/80s when Pluto was closer than Neptune. I'll research their intersection dates.

    As a rule of thumb, halving the distance to an object decreases its apparent magnitude by about $-2.5 \log_{10} 4 ≈ -1.5$. To get Pluto into the visible range, you'd have to decrease the mangitude by about 7.5 relative to its magnitude on Earth, so you'd need to be about 32 times closer to Pluto than the Earth is to (barely) see it with the naked eye. If I've worked my numbers right, this very conveniently works out to be about 1 AU away (maybe a bit less.)

    Pluto and Neptune never get within 160 million km of each other. More like 2.5 billion km at their closest. See: https://astronomy.stackexchange.com/questions/22304/when-and-where-are-pluto-and-neptune-closest-to-each-other

  • No, it cannot. Far from it.


    The closest approach between both planets is roughly 16 AU due to the 3:2 orbit resonance. Pluto will even then be a tiny dot among many with a brightness around 14 mag.


    You can try that with Stellarium yourself, placing the observer on Neptune and looking for Pluto. You just have to find the right time. One such time is approx. in the year 2877.


    Thank you for the year. I just studied Stellarium, looking at Pluto from Proteus, but the closest I got Pluto was in end of 2003 / beginning of 2004 at 27.29 au from me.

    Alright, in spring 2881 I got Pluto as close as 20.05 au from me on Proteus. It wasn't visible even in a good telescope.

    I found an 18.9 au approach in 1896.

    @MikeG Indeed, 18.88 au from me in fall 1896. Still not visible at 70x magnification.

    14 mag? Isn't it the same brightness as what we see from Earth?

    In Stellarium, I found a 9.8 AU distance between Pluto and Neptune, in -2527. Not sure if it's really reliable, though. With a 12.9 mag, as seen from Neptune. Oooooh. And 10 mag at 3 AU in October 99861. XD

    @EricDuminil Pretty sure this is fake news.

    So, does this mean people on Neptune are still perfectly unaware of Pluto's existence?

    People on earth also know about pluto without being able to see it with the unaided eye

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Content dated before 7/24/2021 11:53 AM