Did I see Pluto with my naked eye?

Question

Early this morning going out on the balcony, I looked up on a star chart app to verify it was Jupiter I was seeing. Then I noticed the alignment of Mars, Saturn, and Pluto on the app.

Never being able to identify it before, I stared at where Pluto should be and I'm pretty sure I saw it.

My only question is - since it's said that planets shine and stars twinkle, it did seem that Pluto was flicking a bit. Is this normal? Something to do with the relatively low luminosity and greater length of space?

It wouldn't have been Pluto, it's far too small and faint to be seen without a really powerful telescope. It was most likely a star that just happened to be in roughly the same place. — , Mar 15 '18 at 16:50
I agree with the previous statement. There's absolutely no chance to see Pluto with your naked eye. One can't even see objects of Plutos size in the asteroid belt (which is much closer) with the naked eye. — AtmosphericPrisonEscape, Mar 15 '18 at 17:12
Thanks for setting me straight. Good thing I didn't go into the real world bragging yet. — Jason P Sallinger, Mar 15 '18 at 17:47
Pluto is so small that it fails to fully occult stars. That's small enough to twinkle. But I still think you fooled yourself. — Joshua, Mar 15 '18 at 21:12
If Pluto was visible to the naked eye, it would have been known since antiquity. But it was not, neither were Uranus or Neptune which are closer, larger, and brighter. — swbarnes2, Mar 16 '18 at 17:00
Some asteroids are sometimes naked-eye visible, but they're unlikely to be on your chart, so I reckon there's a small chance it was one of those. — Anton Sherwood, Mar 16 '18 at 20:50

score 103 · Accepted Answer · answered Mar 15 '18 at 18:06

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Pluto is something like magnitude 14. The limit for the human vision is somewhere between magnitude 6 (widely accepted) and 8-ish (highly trained observers with perfect vision in ideal conditions using special techniques - and it's a bit controversial anyway).

There's zero chance that was Pluto. It was definitely a fixed star.

answered Mar 15 '18 at 18:06

Florin Andrei

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The difference is somewhere between 250 to 1000. It means, it is not a little bit fainter to be visible, it should be 1000 times lighter to be visible like a very faint star. – peterh Mar 15 '18 at 19:30
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It surely wasn't Pluto indeed. You cannot be sure it was a star though (e.g. satellite, plane, ...) – Eric Duminil Mar 16 '18 at 20:37
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But a plane must move faster on the sky than a planet, does it not? – mathreadler Mar 18 '18 at 08:06
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@mathreadler: Planes that are far away but flying in your exact direction can be surprisingly bright and stable in the sky. – Eric Duminil Mar 18 '18 at 10:42
Since when are stars "fixed"? ;-) – uhoh Mar 19 '18 at 02:49
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Obviously stars are fixed, or they'd all come crashing down on us. – Vince O'Sullivan Mar 19 '18 at 08:27
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@uhoh "Fixed star" is a commonly used term in astronomy, although nowadays it's more of a historic interest, since we now understand that most star-like objects visible with the naked eye, which appear to be unmoving relative to each other, are indeed stars. Even so, it's still in use, so don't be surprised when you hear it. https://en.wikipedia.org/wiki/Fixed_stars – Florin Andrei Mar 20 '18 at 20:21
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@FlorinAndrei Since it has a latin equivalent (e.g. Wikipedia's reference to stellae fixae) it's officially "a thing". I always enjoy your substantial and authoritative answers btw! – uhoh Mar 21 '18 at 02:10

Haunt_House · Answer 2 · 2018-03-19T05:10:28.523

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As Florin correctly stated, it can't have been Pluto. You have probably looked at it and you have even gotten its light in your eyes. That little itty bitty shine just has no chance to make your retina do anything (edit: Interesting link in the comments. Might be that people actually can sense single photons. Doesn't help at all to see Pluto though).

Stellarium is a nice tool in order to check which star you might have confused with Pluto. This is what it has to offer:

The red crosshair is where Pluto should be and Stellarium doesn't bother to color a single pixel because Pluto is about 14.28 mag. 5 mag difference mean 100 times dimmer, so Pluto is at least 10000 times less bright than many of the stars that you see in this image, let alone the two planets (Mars is about 26 times closer than Pluto atm.).

My guess is that you have seen Pi Sagittarii (HIP 94141) which would be 2.85 mag and lines up nicely with the planets. Unless I'm wrong, it's roughly 37000 times brighter than Pluto

edited Mar 19 '18 at 05:10

answered Mar 16 '18 at 03:29

Haunt_House

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That little itty bitty shine most definitely can make your retina do something: https://www.nature.com/news/people-can-sense-single-photons-1.20282 - your brain just won't pick it up when there's other, more intense signals anywhere. – Michael Borgwardt Mar 16 '18 at 08:29
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@MichaelBorgwardt they tested a whole 3 people... hardly good methodology – Alex Robinson Mar 16 '18 at 10:51
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"other, more intense signals" - such as good old thermal noise in the amplifier stack. – John Dvorak Mar 16 '18 at 12:01
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@Cursed Why? If I want to show that something is possible, showing that it works on 3/3 participants seems good enough to me. (And it's not like that were 3 trials, those were thousands of trials with 3 participants). – sgf Mar 16 '18 at 16:46

Did I see Pluto with my naked eye?

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