# Brightness of daylight on Pluto, in real terms
**URL:** https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430
**Category:** Factual Questions
**Created:** [October 3, 2015, 10:30pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430 "2015-10-03T22:30:19Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [October 3, 2015, 10:30pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/1 "2015-10-03T22:30:19Z")
Pluto looks quite a nice place to visit; I’m thinking of spending a week there between Christmas and New Year. Obviously it’s a long way from the sun, so I know it’s not going to be so warm as the planet you have here, and more importantly to me, not so bright.
How bright is the midday sun on Pluto, in comparison to various familiar light levels on Earth? Bright as a heavily overcast day? Dusk immediately following sunset? Nighttime illuminated by a full moon?
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [October 3, 2015, 10:40pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/2 "2015-10-03T22:40:52Z")
About 250 times brighter than a full moon viewed from Earth.
> [@](#):
>
> The Earth orbits the Sun, on average, at a distance of about 150 million km. Pluto has a very elliptical orbit, but has an average distance of about 5.9 billion kilometers, or roughly 39 times the Earth’s distance from the Sun. Using the method above, the Sun must be 392 = about 1500 times fainter, or more grammatically correctly, 0.00065 times as bright. That’s pretty faint!
>
> Or is it? Well, let’s compare that to how bright the full Moon looks from Earth. To us here at home, the Sun is about 400,000 times brighter than the full Moon, so even from distant, frigid Pluto, on average the Sun would look more than 250 times brighter than the full Moon does from Earth!
From here: [http://blogs.discovermagazine.com/badastronomy/2012/03/15/bafact-math-how-bright-is-the-sun-from-pluto/](http://blogs.discovermagazine.com/badastronomy/2012/03/15/bafact-math-how-bright-is-the-sun-from-pluto/)
ETA: Full article has more details and also shows brightness difference depending on Pluto’s distance from the Sun (since Pluto is in an elliptical orbit).
Oh, and the temperature will be somewhere between about -375 and -400 deg F. Bring a jacket.
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### Author:  [@sbunny8](https://boards.straightdope.com/u/sbunny8)
#### Post date: [October 3, 2015, 10:45pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/3 "2015-10-03T22:45:57Z")
nm
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### Author:  [@sbunny8](https://boards.straightdope.com/u/sbunny8)
#### Post date: [October 3, 2015, 11:08pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/4 "2015-10-03T23:08:17Z")
Pluto’s orbit is eccentric, varying from 29.7 to 49.3 AUs. So the amount of sunlight on Pluto varies from .041% to .011% of what we get on Earth. A bright sunny day on Earth is around 110,000 lux so on Pluto you’d get anywhere from 45 to 121 lux. That’s a bit more than what we see at sunrise or sunset on an overcast day on Earth. [Daylight - Wikipedia](https://en.wikipedia.org/wiki/Daylight)
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [October 3, 2015, 11:28pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/5 "2015-10-03T23:28:33Z")
Here’s another discussion of it, comparing how the Sun would look from each of the planets.
[What would the sun look like from Jupiter or Pluto?](http://astrobob.areavoices.com/2012/01/05/what-would-the-sun-look-like-from-jupiter-or-pluto/) (Includes comparative illustration.)
Note that, from Pluto, the Sun would appear no larger (or not much) than a typical star, yet its brightness would be as others have said above.
> [@](#):
>
> . . . The accepted human eye limit for discerning the shape of an object in the sky is one arc minute or 1/30 the size of the sun or full moon. Only the sharp-eyed among us would be able to see the sun as a disk from Uranus and Neptune, while Pluto would elude all.
>
> Perhaps the most amazing thing about the shrinking sun is that it remains extremely brilliant right on out to Pluto. Not radiant like the way we see it from Earth of course, but brighter than you might suppose. At the dwarf planet’s distance of 3.6 billion miles, the sun shines at magnitude -19 or eight magnitudes fainter than here at home. Standing on Pluto’s methane frosted surface, it would shine about 240 times brighter than the full moon. That’s the power of a star.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [October 3, 2015, 11:37pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/6 "2015-10-03T23:37:13Z")
Cool, so bright enough to read by? I’ll take some books.
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### Author:  [@Mikeisskeptical](https://boards.straightdope.com/u/Mikeisskeptical)
#### Post date: [October 4, 2015, 12:35am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/7 "2015-10-04T00:35:19Z")
> [@Mangetout](#):
>
> Cool, so bright enough to read by? I’ll take some books.
I’d take a gameboy or some cards or something too. It’s a long trip.
Bon voyage!
P.S. Bring back some rocks.
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### Author:  [@burpo\_the\_wonder\_mutt](https://boards.straightdope.com/u/burpo_the_wonder_mutt)
#### Post date: [October 4, 2015, 12:44am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/8 "2015-10-04T00:44:47Z")
This thread from last week, was VERY informative for me. Near the end, is a link to a site showing comparative sunlight between Earth and Pluto. I was amazed, you might be, too.
> **[Pluto -- now in COLOR!](https://boards.straightdope.com/sdmb/showthread.php?t=769868)**
>
> New high-res. photos from the flyby in color: http://finance.yahoo.com/news/sharpest-pluto-photos-ever-released-200954159.html We’ve known for almost 15 years that Pluto was “mostly brown”, but it’s better at high resolution ...
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### Author:  [@Andy\_L](https://boards.straightdope.com/u/Andy_L)
#### Post date: [October 4, 2015, 12:52am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/9 "2015-10-04T00:52:59Z")
Many, many SF writers talk about how dim the Sun would be from Pluto (or even from the Asteroid belt), but Heinlein at least, described light on Pluto (in “Have Spacesuit, Will Travel”) correctly: writing “The ground was covered with snow, glaringly white even under that pinpoint Sun” and “With no disc you could be sure of, it looked like an electric arc.”
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### Author:  [@iljitsch](https://boards.straightdope.com/u/iljitsch)
#### Post date: [October 4, 2015, 11:06am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/10 "2015-10-04T11:06:43Z")
In photographic terms, a sunny day on Pluto is about 10 stops dimmer than the same on earth. So if your iPhone can take a picture at 1/1000th of a second with ISO 32 here on earth, on Pluto it would have to go to ISO 800 and 1/40th of a second.
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### Author:  [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)
#### Post date: [October 4, 2015, 1:03pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/11 "2015-10-04T13:03:14Z")
> [@sbunny8](#):
>
> Pluto’s orbit is eccentric, varying from 29.7 to 49.3 AUs. So the amount of sunlight on Pluto varies from .041% to .011% of what we get on Earth. A bright sunny day on Earth is around 110,000 lux so on Pluto you’d get anywhere from 45 to 121 lux. That’s a bit more than what we see at sunrise or sunset on an overcast day on Earth. [Daylight - Wikipedia](https://en.wikipedia.org/wiki/Daylight)
So let’s say 100 lux. A 40W bulb sends out 450 lumen according to Wiki. Let’s say you are reading at a distance of 2 meters from the bulb. Now a 2 meter radius sphere has an area of roughly 50 square meters. Therefore it seems to me that the bulb at 2 meters has an illumination of only 9 lux. And you can certainly read by at a distance of 2 meters. So bring your book. A 100W bulb would give about 40 lux.
So this suggests that Pluto would be illuminated about as well as a room at night.
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### Author:  [@Oukile](https://boards.straightdope.com/u/Oukile)
#### Post date: [October 4, 2015, 3:44pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/12 "2015-10-04T15:44:49Z")
> [@iljitsch](#):
>
> In photographic terms, a sunny day on Pluto is about 10 stops dimmer than the same on earth. So if your iPhone can take a picture at 1/1000th of a second with ISO 32 here on earth, on Pluto it would have to go to ISO 800 and 1/40th of a second.
Good idea to express it in photographic terms. Let me do it with more details.
2^10.5 is close to 1500. If the Sun is 1500 times fainter, then it is 10.5 stops dimmer. There is no atmosphere on Pluto which will give us a bit more light so I’ll settle for 10 stops.
On Earth in bright daylight, I set my camera to 100 ISO, f/11, 1/100s
As I land on Pluto, I set the dials to:
3200 ISO, f/11, 1/100s -\> this is 5 stops more
3200 ISO, f/2.8, 1/100s -\> 4 extra stops, total 9 stops
3200 ISO, f/2.8, 1/50s -\> 1 extra stop, total 10 stops.
So this is how you would set your camera on Pluto. Nothing that a modern DSLR can’t handle. The shadow would look a bit harsh though so I advise you bring your reflector.
I have shot a few times with similar settings: this is typically what you’ll get in a concert, indoors or outdoors at night, or in a theater, or in a church, or in a pub.
Considering that the light comes from a single spot (the Sun), it must be very directional and cast strong shadows. Think of some indoor concert where the scene is lighted by a single row of spotlights. I imagine that’s how it would look like on Pluto.
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### Author:  [@Derleth](https://boards.straightdope.com/u/Derleth)
#### Post date: [October 4, 2015, 7:41pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/13 "2015-10-04T19:41:01Z")
[NASA has a website where you can input your location (or any location) and it will tell you when the next time the ambient daylight there will be as bright as high noon on Pluto.](http://solarsystem.nasa.gov/plutotime/) Of course, this assumes there aren’t any clouds or anything else which would tend to darken the skies, and it doesn’t take light pollution from streetlights and so on into account.
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### Author:  [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)
#### Post date: [October 5, 2015, 2:24am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/14 "2015-10-05T02:24:14Z")
> [@engineer\_comp\_geek](#):
>
> …
> Oh, and the temperature will be somewhere between about -375 and -400 deg F. Bring a jacket.
Brrr… that’s pretty cold. Maybe you would prefer a destination like [Barrow, Alaska](https://en.wikipedia.org/wiki/Barrow,_Alaska), which usually doesn’t get much colder than -20 to -30 deg F. I would still recommend a jacket, though.
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### Author:  [@Pleonast](https://boards.straightdope.com/u/Pleonast)
#### Post date: [October 5, 2015, 3:41am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/15 "2015-10-05T03:41:24Z")
How long could one stare at the Sun while on Pluto before seriously damaging your eyes?
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### Author:  [@iljitsch](https://boards.straightdope.com/u/iljitsch)
#### Post date: [October 5, 2015, 7:12am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/16 "2015-10-05T07:12:22Z")
Wouldn’t the brightness of the surface of the sun appear the same, with the difference in the total amount of light being smaller because the disc of the sun appears smaller? In that case damage will occur just as quickly as on earth, only the damaged area of your eye will be smaller.
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [October 5, 2015, 9:13am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/17 "2015-10-05T09:13:02Z")
A previous discussion on this subject here;
> **[At what distance could a human look directly at the sun without eye damage?](https://boards.straightdope.com/sdmb/showthread.php?t=729356)**
>
> On NPR.org there was an article about the Mars explorer catching a partial solar eclipse (Phobos being too small to fully obscure the sun). I asked if I would suffer eye damage if I looked at the sun directly on Mars, since it is so far away. ...
this seems to boil down to -
…don’t look directly at the Sun from Pluto.
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### Author:  [@iljitsch](https://boards.straightdope.com/u/iljitsch)
#### Post date: [October 5, 2015, 10:38am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/18 "2015-10-05T10:38:53Z")
> [@eburacum45](#):
>
> A previous discussion on this subject here;
There’s no denying it anymore, I (and everyone else here) needs to go get a life.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [October 5, 2015, 11:00am UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/19 "2015-10-05T11:00:49Z")
Yeah, looking at the Sun on Pluto would be just as damaging as from Earth (perhaps slightly more so, due to less atmosphere); it’d just damage a smaller spot on your retina.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [October 5, 2015, 6:46pm UTC](https://boards.straightdope.com/t/brightness-of-daylight-on-pluto-in-real-terms/733430/20 "2015-10-05T18:46:41Z")
> [@Chronos](#):
>
> Yeah, looking at the Sun on Pluto would be just as damaging as from Earth (perhaps slightly more so, due to less atmosphere); it’d just damage a smaller spot on your retina.
That effect must tail off with distance eventually, or all the stars would burn pinholes in our eyes.
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