<p>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). </p>

<p><a href="http://stellarium.org" rel="noreferrer">Stellarium</a> is a nice tool in order to check which star you might have confused with Pluto. This is what it has to offer:</p>

<p><a href="https://i.sstatic.net/UmpQ5.jpg" rel="noreferrer"><img src="https://i.sstatic.net/UmpQ5.jpg" alt="Stellariun screenshot showing Saturn, Mars and Pluto"></a></p>

<p>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.).</p>

<p>My guess is that you have seen <a href="https://en.wikipedia.org/wiki/Pi_Sagittarii" rel="noreferrer">Pi Sagittarii</a> (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</p>

CC BY-SA 3.0
2018-03-16T08:29:38.283Z
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
CC BY-SA 3.0
2018-03-16T10:51:02.893Z
@MichaelBorgwardt they tested a whole 3 people... hardly good methodology
Alex Robinson
CC BY-SA 3.0
2018-03-16T12:01:16.077Z
"other, more intense signals" - such as good old thermal noise in the amplifier stack.
John Dvorak
CC BY-SA 3.0
2018-03-16T16:46:01.317Z
@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
CC BY-SA 3.0
2018-03-16T03:29:55.770Z
2018-03-19T05:10:28.523Z
2018-03-19T05:10:28.523Z
Haunt_House
<p>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).</p>

<p>There's zero chance that was Pluto. It was definitely a fixed star.</p>

CC BY-SA 3.0
2018-03-15T19:30:52.757Z
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
CC BY-SA 3.0
2018-03-16T20:37:47.457Z
It surely wasn't Pluto indeed. You cannot be sure it was a star though (e.g. satellite, plane, ...)
Eric Duminil
CC BY-SA 3.0
2018-03-18T08:06:17.673Z
But a plane must move faster on the sky than a planet, does it not?
mathreadler
CC BY-SA 3.0
2018-03-18T10:42:51.800Z
@mathreadler: Planes that are far away but flying in your exact direction can be surprisingly bright and stable in the sky.
Eric Duminil
CC BY-SA 3.0
2018-03-19T02:49:18.270Z
Since when are stars "fixed"? ;-)
uhoh
CC BY-SA 3.0
2018-03-19T08:27:33.453Z
Obviously stars are fixed, or they'd all come crashing down on us.
Vince O'Sullivan
CC BY-SA 3.0
2018-03-20T20:21:20.540Z
@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
CC BY-SA 3.0
2018-03-21T02:10:55.073Z
@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
CC BY-SA 3.0
2018-03-15T18:06:47.107Z
2018-03-15T18:06:47.107Z
Florin Andrei
<p>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.</p>
<p>Never being able to identify it before, I stared at where Pluto should be and I'm pretty sure I saw it.</p>
<p>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?</p>

CC BY-SA 3.0
2018-03-15T17:12:56.587Z
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
CC BY-SA 3.0
2018-03-15T17:47:13.483Z
Thanks for setting me straight.  Good thing I didn't go into the real world bragging yet.
Jason P Sallinger
CC BY-SA 3.0
2018-03-15T21:12:19.910Z
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
CC BY-SA 3.0
2018-03-16T17:00:11.073Z
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
CC BY-SA 3.0
2018-03-16T19:34:03.057Z
Marvin, maybe ?  EDIT: sorry, he's from Mars
Jason P Sallinger
CC BY-SA 3.0
2018-03-16T20:50:50.797Z
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
CC BY-SA 3.0
2018-03-18T21:49:08.897Z
On planets twinkling: "[why does venus flick?](https://astronomy.stackexchange.com/q/10455/22261)"
outis
<pluto><naked-eye>
Did I see Pluto with my naked eye?
Jason P Sallinger
# Did I see Pluto with my naked eye?

(Asked by: username_0 on 2018-03-15)

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?

**Tags:** pluto, naked-eye
> **Comments:**
> **username_1**: 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.  
> **username_0**: Thanks for setting me straight.  Good thing I didn't go into the real world bragging yet.  
> **username_2**: Pluto is so small that it fails to fully occult stars. That's small enough to twinkle. But I still think you fooled yourself.  
> **username_3**: 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.  
> **username_0**: Marvin, maybe ?  EDIT: sorry, he's from Mars  
> **username_4**: 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.  
> **username_5**: On planets twinkling: "[why does venus flick?](https://astronomy.stackexchange.com/q/10455/22261)"  

---

## 2 answers

### Answer by username_11 on 2018-03-15. Score: 103 | Accepted answer

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.

> **Comments:**
> **username_12**: 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.  
> **username_13**: It surely wasn't Pluto indeed. You cannot be sure it was a star though (e.g. satellite, plane, ...)  
> **username_14**: But a plane must move faster on the sky than a planet, does it not?  
> **username_13**: @mathreadler: Planes that are far away but flying in your exact direction can be surprisingly bright and stable in the sky.  
> **username_15**: Since when are stars "fixed"? ;-)  
> **username_16**: Obviously stars are fixed, or they'd all come crashing down on us.  
> **username_11**: @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  
> **username_15**: @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!  

---

### Answer by username_6 on 2018-03-16. Score: 18

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](http://stellarium.org) is a nice tool in order to check which star you might have confused with Pluto. This is what it has to offer:

[![Stellariun screenshot showing Saturn, Mars and Pluto](https://i.sstatic.net/UmpQ5.jpg)](https://i.sstatic.net/UmpQ5.jpg)

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](https://en.wikipedia.org/wiki/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

> **Comments:**
> **username_7**: 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.  
> **username_8**: @MichaelBorgwardt they tested a whole 3 people... hardly good methodology  
> **username_9**: "other, more intense signals" - such as good old thermal noise in the amplifier stack.  
> **username_10**: @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).  

---

