Why Am I Staring at the Sun?

Jan 25

Looking directly at the Sun is something you should never do, but what if you really needed to?

CORRECTIONS

at 17:11, this conversion is inaccurate. 729in² should be 0.47m²
at 17:34, this conversion is inaccurate. 135in² would be 11.76m²
(noticed by youtube viewer aaron32190)

at 19:45, the denominator in the middle equation has already been squared, so the exponent of 2 should fall inside the parenthesis to indicate the unit m², rather than a value that has yet to be squared
(noticed by youtube viewer aaron32190)

at 20:00, this conversion is inaccurate. 1m and 5m should become 100cm and 500cm for the near and far radius, respectively.
(noticed by youtube viewer aa18812)

at 25:55, I say "magnitude of -1.47" when I meant -1.46. The distances that follow were calculated for -1.46, so this is just a minor misspeak.
(noticed by me)

— Citations —

Info.

"80% of folks in the US, 60% in Europe, and more than a third of the entire global human population lived in areas that are too light-polluted to see the Milky Way."
timecode 4:59

the new world atlas of artificial night sky brightness
2016, Falchi, et al.
Science Advances, Vol 2, Issue 6
§ results, ¶ "We found that about"

https://www.science.org/doi/10.1126/sciadv.1600377

"He wrote a letter to John Locke in 1692 where he describes an experiment gone wrong almost 30 years prior, back when he was a young man."
timecode 6:10

Bill Bunker's account of looking into a telescope pointed at the Sun without a protective filter.
timecode 43:52

eye injuries of early solar observers
2020, Dr. Young
SDSU
A: § Newton

https://aty.sdsu.edu/vision/others.html

"Up to 85% of stars in the Milky Way galaxy are red dwarf stars."
timecode 11:28

RECONS census of objects nearer than 10 parsecs
2018 RECONS
§ bottom chart, "M stars" / "all stars"

http://recons.org/census.posted.htm

"Some of these stars are so much larger ... than the Sun, it's comical."
timecode 12:03

Fundamental properties and atmospheric structure of the red supergiant VY Canis Majoris
2012, M. Wittkowski et al.
A&A Volume 540, April 2012
p. 4, table 2

https://www.aanda.org/articles/aa/abs/2012/04/aa19126-12/aa19126-12.html

"Sirius A has a magnitude of -1.46."
timecode 25:20

apparent brightness of Sirius A
1991 Bright Star Catalogue, 5th Revised Ed.
row "Vmag"

https://vizier.cds.unistra.fr/viz-bin/VizieR-5?-ref=VIZ657c73de35bcfd&-out.add=.&-source=V/50/catalog&recno=2491

"Sirius A was ... -1.44m in 1997."
timecode 25:20

apparent brightness of Sirius A
1997 The Hipparcos and Tycho Catalogues / ESA
row "Vmag"

https://vizier.cds.unistra.fr/viz-bin/VizieR-5?-ref=VIZ657c753737c73a&-out.add=.&-source=I/239/hip_main&recno=32325

"We need to know the output of the Sun, its stellar luminosity. ... It's 3.83x10^26 watts."
timecode 25:27

sun's stellar luminosity
2022, Dr. David R. Williams
NASA
row "Luminosity"

https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

"The Sun should appear to have a magnitude of -1.47 (sic) at a distance of a little over half a parsec out, or a bit over 100,000 astronomical units."
timecode 25:51

3.83×10^26 watts as apparent magnitude of -1.47
WolframAlpha
§ Results

https://www.wolframalpha.com/input?i=3.83%C3%9710%5E26+W+as+apparent+magnitude&assumption=%7B%22FS%22%7D+-%3E+%7B%7B%22LuminosityApparentMagnitudeDistance%22%2C+%22d%22%7D%7D&assumption=%7B%22F%22%2C+%22LuminosityApparentMagnitudeDistance%22%2C+%22m%22%7D+-%3E%22%E2%88%921.47%22

"For context, this is 20% of the way to Sirius, itself."
timecode 26:04

Sirius overview
Wikipedia
¶ 2

https://en.wikipedia.org/wiki/Sirius

"And it's right on the outer edge of the theoretical Oort cloud."
timecode 26:04

Oort cloud overview
Wikipedia
¶ 1

https://en.wikipedia.org/wiki/Oort_cloud

"A full Moon at its brightest tends to have an apparent magnitude of about -12.9."
timecode 26:48

full moon maximum brightness
Wikipedia
§ infobox, § explanatory notes "c"

https://en.wikipedia.org/wiki/Moon

"582 astronomical units, this is about how far out Voyager One got by about the year 2140."
timecode 27:06

Voyager FAQ
JPL / NASA
§ Present Status

https://voyager.jpl.nasa.gov/frequently-asked-questions/fast-facts/#:~:text=Voyager%201%20is%20escaping%20the,about%203.6%20AU%20per%20year.

"Over here, we can see this chart that is featured on Wikipedia and it catalogues a variety of magnitudes and what they relate to."
timecode 29:00

apparent magnitude overview
JPL / NASA
§ List of apparent magnitudes

https://en.wikipedia.org/wiki/Apparent_magnitude

"since the mid-20th century ... welding filters replaced potentially hazardous viewing materials such as glass with a deposit of soot"
timecode 31:55

historical use of welding filters
2021, B. Ralph Chou et al
AJ 162 103
§ Introduction, ¶ 4

https://iopscience.iop.org/article/10.3847/1538-3881/ac013e

"[welding filters are] a time-honored tradition. It's been used to look at the Sun for a long time. According to the AAS ... this is more than enough to safely observe the Sun."
timecode 31:55

welding filter safety
AAS
§ welding filters

https://eclipse.aas.org/eye-safety/safe-viewing#welding

"This is referred to as 'black polymer' which contains carbon particles suspended in a resin matrix."
timecode 35:22

black polymer material
2023, B. Ralph Chou
AAS
p. 5

https://eclipse.aas.org/sites/eclipse.aas.org/files/AAS-Chou-Tech-Report-Solar-Eclipse-Eye-Safety-2023.pdf

"They just analyzed shade 12 welding glass."
timecode 37:50

ISO 12312-2:2015 details
AAS
§ Transmittance

https://eclipse.aas.org/eye-safety/iso12312-2

Media

m1 - timecode 10:16

Hertzsprung-Russell diagram
2006, Richard Powell
modifications: vectorized and given new visual treatment

http://www.atlasoftheuniverse.com/hr.html

m2 - timecode 11:50

proxima centauri photo
2013 ESA/Hubble & NASA

https://esahubble.org/images/potw1343a/

m3 - timecode 42:24

solar telescope photos
2022 Lunt

https://luntsolarsystems.com/

CREDITS

Brandt Hughes
research, writer, hosts, camera operator,
audio engineer, music production, sound design,
editor, colorist, caption writer

Kinnon Martin & Annaliese Martin
telescope footage

Jeff McLaughlin
production assistance

Nathan Zimmerman
production assistance

MUSIC

"Limitations"
"Suns of the Dark Sky"
"The Sun Stares Back"
"It Keeps Expanding"
"Derivations"
"Asteroid Belt Vacation"
"Lord Sun"
"Paperwork"
"The Maker"

all produced by Brandt Hughes

available to download on
patreon bandcamp

Transcript

CHAPTER 1:
FATHER AND SUN

>> Well my stars.

What do we have here?

>> No way. They're yours‽ That is so cool. I'm not sure about this one. It's pretty bright, so I can't seem to get a good look at it.

>> Oh boy, okay. No, I'm talking about you.

>> Oh, what am I doing here? I don't know. I'm just present.

>> ...Right. Well I was thinking a little bit more metaphysical or historical. Or even really just a name but I like your answer all the same because if you take a look around presence is all-too-rare.

This is nice though, yeah? I like this for us. Can you do me a favor though? Please stop looking at the Sun.

>> But why?

>> All right, fair question. Because it can harm you.

>> Oh.

>> It can damage your eyes quite severely in some cases. Now that might feel unfair and it is. But that's the burden that someone carries when they have curiosity trapped inside of them. It is sometimes the cost that we have to pay for having limitations, but still wanting to know. So please, you can look anywhere else. Just... not directly at the Sun.

>> I think I understand your concern, but this is just simply what progress looks like. See, you were busy looking at the moon so I could get dizzy looking at the Sun.

Bars.

>> Everything you just said was nothing.

>> That is maybe the meanest thing I have ever heard in my entire life, but it's already bygones and I could really use your help. You're telling me not to look at the Sun, but I have to. I'm telling you, something is not right up there.

>> Do whatever you want. Just know that there are consequences to your actions. If you keep looking at the Sun, you're not going to be able to see much else. I just need you to know that I'm looking out for you. You know, there's going to be a day when--

>> -when you're not complaining about something? Not likely! Boom. You see what I did th--

Damn that's cool! Man, if I ever die, that's how I want to go... as a hat.

CHAPTER 2:
A MUNDANE EXCEPTION

Well, I really wanted to look at it, and I still do. I have to.

But... Now I'm too afraid to look directly at it. So instead I sat here as the Sun set. But the sky dissolved into this lightly salted canvas. Apparently, these are also stars.

Most are lost to the opaque haze that surrounds our cities, but some of the brightest can still shine through. Vega, Altair, Sirius, Rigel, Betel-- Oh man.

Our own galaxy, The Milky Way, is a lost heritage of sorts. We are embedded inside of it. If you pick any direction, you'll be looking through more of it. And yet I've never actually seen with my own eyes the unmistakable collective glow of our hundreds of billions of neighboring stars.

By the early 21st century, most people couldn't. 80% of folks in the US, 60% in Europe and more than a third of the entire global human population lived in areas too light-polluted to see the Milky Way.

Despite living in this isolation, we can still see enough stars to feel an intuitive dissonance. That during the day one star could be so caustic to the eye, yet during the night so many can pleasantly dazzle the gaze. After all, the Sun is a star just like all the others, right? But the problem remains. I still need to see it. And I'm now fully convinced that --- was right.

It would be unwise for me to just look directly at it. Certainly that would be a bad idea. I mean, beyond my own naiveté, it's hard to imagine that somebody would be foolish enough to just stare directly at it.

CHAPTER 3:
THE HAUNTING OF ISAAC NEWTON

That brings us back however many hundreds of years to Sir Isaac Newton, historically significant smart person. He was foolish enough to stare directly at it.

He wrote a letter to John Locke in 1692 where he describes an experiment gone wrong almost 30 years prior, back when he was a young man.

Newton was trying to form afterimages. You know, where you look at something bright and the image of that light lingers in your vision, but then fades a few moments later. And where else might you find a distinct bright light in the 1600s other than... well, the Sun?

So he sat himself in a dark room to better see the after images. Then he would crack open a door and let a bit of sunlight flood into the room. He placed a mirror into this beam of light and angled it to see the Sun. This worked beautifully.

He looked towards a dark corner of the room and the after image lingered and faded just as planned. But he quickly ran into a problem. After images are so ephemeral, that your time to study and observe them are extremely limited. So the only way to continue his study was to conduct the experiment again. Remember that in this dark room his eyes had dilated, letting the maximum amount of light enter, resulting in more damage. But this didn't concern him yet, so needing more information, he carried on with the third attempt.

However, there would not be a fourth attempt. Because now, a few hours into the experiment, he started to notice something unexpected. He could will the image to return so vivid, as if he looked upon the sun anew.

This novelty soon contorted into a wicked haunting as the sun became easier and easier to conjure, but harder to vanish. As panic sets in, the brilliant echo then seems to corrupt his left eye, which didn't even look at the Sun.

Just a few hours later, he had locked himself in a dark room in hopes of recovery. But even in this isolation, eyes closed, sound of crickets in the night, he still couldn't avoid the Sun staring back at him. He stayed there for three long days, devoting himself to evict this ever-present Sun from his sight and from his mind.

It was a week in all before he regained the use of his eyes and a few months more before he stopped seeing that searing white spot in his vision.

His eyes may have healed, but the experience shook him so profoundly that even though 30 years had separated him from these events at the time of his writing, he still feared that he might think of the Sun and it could reappear in his sight.

CHAPTER 4:
MAIN SEQUENCE

So the Sun is dangerously bright. We know this, vicariously, due to Isaac Newton's curiosity and slight misfortune of being born before the invention of the light bulb. Although, I can't imagine looking at a light bulb for a long time would be good for your eyes either.

But to protect my eyes, we must know thine enemy. The Sun is a star. Of course. Classic Sun.

But is it like all of the other stars, as I had assumed earlier? Are all stars quite so bright?

Well, no-- eh. Sort of? It depends on how you define the question. Right?

Stars are categorically bright as far as objects in the universe go. If you compare it to something like a baseball or dirt, an amoeba, moss, whatever! The star is going to be brighter.

There are very few things that are brighter than stars, but don't let that fool you because stars are a wildly diverse category of objects.

If we take a bunch of nearby stars and we plot them out on a diagram by their brightness and color, we have what's called a Hertzsprung-Russell diagram, and uh you can immediately see a few different distinct formations.

These are subcategories of stars, right? Because stars are so different that we need to break it up into little groups so that way we actually know what we're talking about.

The Sun is what's called a main sequence star, which just means it's on this main diagonal branch, there. Our Sun is also a G type star.

What does that mean? Why a G? Some questions were never meant to be answered.

I don't kn-- I think it's a chemistry thing. Really it just kinda ends up being like it's a color. It's the--It's the star with G type color.

And so if we look at the diagram, we can just--we can just see that it's right there. And if we compare it to a bunch of other stars, we see that the Sun is not really much of an outlier.

It's really doing like the star equivalent of not making eye contact so that way you don't have to interact with it. It's just blending in. Very middle of the road, nothing too exceptional.

But this is a little misleading because the Sun is actually brighter than the vast majority of stars. Straight up.

85% of stars in the Milky Way galaxy are red dwarf stars. Red dwarf stars are so dim. How dim are they? They are so dim that we can't see a single one with the unaided human eye from Earth, despite the fact that the star that is nearest to the Sun, our closest neighbor, is a red dwarf star. That sneaky little guy.

So from that we can intuit that here from Earth we can really only see the brightest stars. And when I say brightest, I mean it. Some of these stars are so much larger and brighter than the Sun. It's comical to even compare them.

But how come all stars, even these comically large stars, why are all of them appearing smaller and dimmer than the Sun? This may seem like a basic question, but don't underestimate the power of a basic question.

Let's think through some of the possible explanations here. One is, you know, there's a bunch of interstellar dust and nebula gases and just in general stuff getting in the way. Right? And that can block light and that can make stars appear slightly less bright.

Another possible contributing factor could be redshifting. Right? As stars move away from us, the light gets kind of stretched and elongated into lower and lower frequencies of light. And if this happens enough, some of that light can still reach us but it can be such low frequency that we can't see it. It's no longer in the visible spectrum of light. Because humans, we just have--we just have this narrow little band of sensitivity.

But I don't think this contributes to all of the dimming and we haven't gotten to the size yet. So there's one last factor, and I think it predominantly outweighs the others because it does describe the dimming and the size discrepancy.

This single word really characterizes the defining trait of outer space, as I see it. Of course, I'm talking about...

CHAPTER 5:
DISTANCE

Distance! Stuff sure is far apart. More so than any earthbound human is prepared to conceptualize. But now that we're thinking about distance, that opens us up to a question that I can't wait to find the answer to.

How far does a person have to be from the Sun before the Sun just becomes another star in the night sky? Where you can look upon it with wistful ignorance of its terrifying power. I'm not talking about using protective equipment or looking at the Sun through atmospheric phenomena or anything like that. I'm talking about just strictly using distance to protect your eyes. Where does that threshold exist?

Honestly, I don't know. Is it as close as any of the planetary orbits? Is it even within the solar system?

Well, before we get too deep into this question, we should hit some fundamentals first. I've told you that stars appear less bright at a distance, but to understand how much less bright, we should discuss the inverse square law.

So what is the inverse square law? Great question. Thank you. I thought you'd never ask. The inverse square law is a description of a finite property, usually some form of energy, that starts as a point and then extends out in all directions. And because it's finite, it gets less dense as it does so. Really it's just geometry, and because it's geometry, we see it across nature all the time. And the inverse square law helps us describe things like the behavior of sound, gravity, or even light.

To really reinforce this idea, I think you'll need to see it in action though. But in order to do so, we'll need to scale everything way, way down. Because otherwise we're dealing with distances that are not scaled to the human experience and it will just be really hard to wrap our minds around. But stars are so extreme. I can't imagine how difficult it'll be to find an appropriate analog that is at the correct, small scale. It just seems farcical. How am I going to find anything (increasingly exasperated) that even remotely resembles or compares to something so drastically huge and so immensely--

Oh, I did it. That was easy. I just discovered a micro star and uh, it only outputs 360 watts of energy. I've never seen anything like it in all my day. Let me just get this set up right over here. There we go. Nice.

As we know, stars emit light in all directions, but this demonstration is just going to work better and be more clear if we only look at a small slice of the ever-expanding sphere of light. So I've taken the micro star and I have trapped it inside of this box. I have taken to calling it a star box and it blocks all of the light except for what can shine through this little window right here.

Our records indicate that the people of this time not only had star boxes, but really loved them. They were such a curious people. It's said that there was a star box on just about every city corner and folks would often meet up at their nearest star box to socialize and to admire the light. Why were they so fascinated by this? Well, it's easy to see. Check it out.

At one meter away, our patch of light spans about 27 inches horizontally and 27 inches vertically. Forgive my mixing of units. And this gives us an area of about 730 square inches. At a vertical slice of one meter in distance, the patch of light is still the same size 27 inches across in both directions. However, at a distance of five meters, we have an opportunity to use our powers of observation. The light is now 135 inches across in both directions. This gives us a surface area of over 18,000 square inches which happens to be 25 times the area. But notice that our light source didn't change at all. So it's the same amount of light, but it's hitting a larger area.

So in effect, light is being spread thin. Not strictly speaking, of course, light doesn't have thickness quite like that. I'm speaking metaphorically. You get the idea. Light is being distributed over an area.

A sample taken at five meters is going to be 1/25 as bright as a sample of the same size taken at one meter. The inverse square law describes this behavior.

Now that we have context, we must confront The Dreaded Math Section. It's fine. Math is scary to me, but this is honestly quite manageable. The real math sickos won't even break a sweat.

We start with our source light, which is outputting 360 watts in a spherical wavefront of light. Well, in reality it's more complicated than that, but we're just conceptualizing a hypothetical singular wavefront. A vertical slice of sorts.

Anyway, this wavefront keeps expanding until something gets in its way, and then it bounces off in a wavelike manner. As the light spreads out, it doesn't gain or lose energy, it just gets distributed over more area. So the entire wavefront will always add up to 360 watts regardless of size.

Now, remember, we took two measurements, a near sample at a distance of one meter and a far sample at a distance of five meters. I specifically wanted both of these samples to cover an area of one centimeter squared. So calculating how much light hit each sample is actually fairly straightforward.

We just have to take the source strength, which is 360 watts and divide it by the surface area of that sphere. Surface area of a sphere is defined by four pi r squared.

The radius is the distance from our sample to the source. So if we plug one meter into the radius and crunch the numbers, we get 28.6479. This is called our surface intensity, and it's how many watts cover a square meter. Because those are the units that we use for the source and for our radius.

Our samples are one centimeter squared, though. So if we use centimeters for r instead, we'll get how much light hit our sample and only our sample, at least under ideal conditions.

In doing so, we see that the near sample got 0.28648 watts per square centimeter. Our far sample was at a distance of 50 centimeters. And if we plug that in, we find that our far sample got 0.01146 watts per square centimeter.

It's quite evident that the near sample received 25 times more light. But if we're just trying to compare how much more or less light one sample received compared to the other, we can really simplify the formula here.

We start with the surface intensity formula for the far sample, and then we divide that by the same formula for the near sample.

Oh man, what a jumble. Look at this mess! But remember that by dividing something, say, ten divided by five, that's equivalent to multiplying by its inverse, so ten times one over five. If we apply that same principle to our formula here, we get a much cleaner s four pi radius near squared over s four pi radius far squared.

Now, look at how much we can reduce with this. Our source outputs the same amount of light during both measurements, so those cancel out. Four and pi can also be reduced. Oh now we're cooking.

We just have r squared on top and bottom. But there's one last thing we can do to really make this sing. Instead of measuring how far each radius is from the source of light, we can measure them as a proportion of the first radius.

So how many times further out is the far radius compared to the near radius? We do this quite simply by dividing the top and bottom by the near radius.

Now our formula is unitless, and our numerator reduces to one. That gives us one over the far radius divided by the near radius squared.

This is our generalized inverse square law formula. Ultimately, it's just the relationship between the surface area of two spheres of differing sizes.

So that was just a surface level explanation because brightness is a surprisingly complicated concept, but I just wanted you to understand how the intensity of light can drop off with distance.

But with that out of the way, let's start really seriously thinking about this question. And maybe we can devise a methodology for figuring out some safe viewing distances.

CHAPTER 6:
SKYMARKS

The key to figuring this out is to use the right unit of measure, and for that, we're going to turn to astronomers and use what's called magnitude.

This is going to unlock so much for us because magnitude is already specifically designed to compare the brightness of stars. So it'll simplify our calculations with figuring out how bright a star should appear to be at various distances.

Magnitude is a bit of a funny unit though. Not ha-ha funny, necessarily. More like ambiguously laughing in response to something that somebody said to you, but you didn't understand what they said and you want to play it cool and not let them know that you didn't understand it kind of funny.

To start with, you might hear folks just refer to magnitude, but there are actually two distinctly different magnitudes. There is absolute magnitude and apparent magnitude.

You can think of absolute magnitude as the intrinsic brightness of a star. It's a measure of how bright any given star is, as measured ten parsecs from the star itself. So it has a frame of reference relative to the star.

Apparent magnitude on the other hand, is just a measure of how bright the star appears to be from somewhere else. So you give it a frame of reference which is always assumed to be Earth, and the measurements should include the effects of atmosphere and distance, stuff like that, anything that would change the appearance as seen from Earth.

It's worth knowing both measurements exist, but I'm just going to use apparent magnitude, because what's important here is knowing how bright the Sun appears to be from the frame of reference of our eyes.

Magnitudes are expressed as numbers either positive or negative, usually positive, and are rather close to zero. It scales such that Vega lands pretty near but not exactly on zero.

But magnitude is measured inversely. So objects brighter than Vega have increasingly negative magnitudes and objects more faint have positive magnitudes.

And if that wasn't enough, magnitude is also logarithmic. So every full integer is about two and a half times difference in brightness. For example, a two magnitude star is about two and a half times brighter than a three magnitude star. But then it's about 100 times brighter than a seven magnitude star.

So let's start comparing to some landmarks. Skymarks? Points of reference.

The brightest object in the night sky is Sirius A, the brighter half of an incredible binary star system. One of my absolute favorites. And we could look at Sirius A all we want, no problem, no harm to the eyes. So it seems like a great place to start.

Sirius A has a magnitude of -1.46. Now, to figure out how far the Sun would have to be to match that, we need to know the output of the Sun, its stellar luminosity. Luckily, smarty-scientist types already figured this out. It's 3.83 times ten to the 26 watts, a hell of a lot brighter than that little star in our star box.

Knowing that, we can punch these numbers into our personal computers or write it out if that's what tickles your brain. And on the other side, we find that the Sun should appear to have a magnitude of -1.47 at a distance of a little over half a parsec out, or a bit over 100,000 astronomical units.

For context, this is 20% of the way to Sirius itself, and it's right on the outer edge of the theoretical Oort cloud.

It's hard to overstate how extraordinarily far away this is. Depending on how you define the boundaries of the solar system, it might be within it, but only just barely, or it might be well outside of it.

My eyes don't exactly strain looking at Sirius A so I have a hard time imagining that it's especially close to that threshold that we're looking for. But thinking about it now, though, I'm remembering something that might help us get a bit closer.

>> Go look at the moon. Like really look at it.

>> We have to look at the moon. A full moon at its brightest tends to have an apparent magnitude of about -12.9. That's 37,000 times brighter than Sirius! And we can still look at it just fine.

So how far would the Sun have to be to match the brightness of a full moon? That would be 582 astronomical units.

This is about how far out Voyager One got by about the year 2140, and it's halfway to the furthest point in dwarf planet Sedna's orbit.

>> Query deferred.

CHAPTER 7:
HISTORY OF INFORMATION

>> I'm going to-- I'm going to need a moment. Um... Suffice to say, just because Sedna's at 582 AU sometimes doesn't mean it always is. Eccentricity and all.

Um, I don't want to talk about it. Forgot my space suit. I forgot my space suit, okay!

It doesn't matter. I could hardly see the Sun anyway. It was so small. It was like a pinpoint of light. And I was really disoriented too. You know, outter space.

So now we have a new problem. The only thing I can think of that is in the sky that is brighter than the moon is the Sun. So we are fresh out of things to compare brightnesses to and we'll need a new approach to push us closer to this threshold.

I didn't want to resort to this, but I'm not sure I have a choice anymore.

grave. wiki underscore max brightness enter. force underscore center view enter. grave.

Over here, we can see this chart that is featured on Wikipedia and it catalogs a variety of magnitudes and what they relate to. Among them is one that says that -25 is the threshold at which the human eye experiences pain. It doesn't say anything about damage per se, but otherwise it sounds a whole lot like what we're looking for.

So if we crunch the numbers, that puts safe-viewing distance at a mere 2.2 astronomical units, which is just past Mars and right on the inside of the asteroid belt between Mars and Jupiter.

On a human scale, this is extraordinarily far away, but on a space scale, this is really quite close. But there are some caveats.

If you're clever, you might think that the problem is in logistically achieving this distance. If we move the Sun out to that distance, well... we cause a whole lot of problems for the whole solar system and Earth here as well. If we move ourselves out to that distance, well now we no longer have a whole planet's worth of atmosphere absorbing and scattering harmful cosmic rays, which can cause us some real problems.

But I'm not really concerned with either of those. We can engineer solutions to that if we really wanted to, but that's not the focus of today. So I'm not even thinking about that. What I am thinking about is that chart.

Where did this number come from? -25 magnitude.

Look, I like Wikipedia probably more than most, but all information comes with what amounts to a paper trail, a lineage of thought. It's that history that gives you context to know whether or not you can trust the information.

This information wasn't cited at all. It was added in 2016 by a user, and that is their only contribution.

So where did it come from? Did it come from a reputable scientific or medical journal? Did it come from a textbook? Did it come from... personal experimentation?

I simply have no way to know. And because it falls on such a clean, rounded off number, it feels extremely suspect to me. To tell you the truth, it feels like somebody just took a guess. And I have to treat it as a guess until it gets a history that I trust more than an IP address.

So now we have a range with an asterisk on the low end. But you know what? Humans are crafty and they love to put themselves at risk of bodily harm. So I'm sure they've engineered some sort of solution to look at the Sun from little ol' Earth here.

CHAPTER 8:
SEEING THE SUN

First up is welding filters. This is a time-honored tradition. It's been used to look at the Sun for a long time.

According to the AAS, the American Astronomical Society, this is more than enough to safely observe the Sun, which you can see is that bright spot right there. However, it has to meet two criteria in order to do so.

One, it can't be an auto-darkening filter. Some of these will change shade depending on what you're looking at, and if you're looking at the Sun, that puts your eyes at risk. You want a static single shade.

Two, it has to be a shade 12 or darker. The higher the number, the darker the shade of glass.

12 is often described as making the Sun look uncomfortably bright, but it's still technically safe to use. Shade 15 on the other end is described as making the Sun look unpleasantly dark, so shades 13 and 14 are most commonly recommended.

This is a shade 14 glass. And after using it a few times, I find the Sun to be pretty comfortable to look at through this. However, I have two problems with this technique in general and it's really more of a problem of convenience.

One, it's made out of glass and it's really dark, so it's highly reflective. So you sort of have to use like the photographer hood technique to reduce reflections or just hold it really close up to your eye.

Two, color reproduction is not a high priority with welding glass, so everything has this gross green tint to it.

It's fine. You can totally see the Sun and you can see details in the Sun. But you know, compared to some of our other techniques, it's just not the prettiest one.

And then we have basic solar filters like this. It comes in a variety of forms.

You can use it for camera lenses or you can use them for telescopes. If you have enough magnification, you can see some really great detail in the Sun. It's cost effective and they work great.

The same material even comes in a wearable form, which is typically marketed as solar eclipse glasses, but it doesn't actually have to be a solar eclipse for you to use them.

You can... you can just look at the Sun with eclipse glasses on a normal day.

Check these out. They are gorgeous in their simplicity, and they are the key to everything.

They're kind of a cardstock material for the frame, and the lens is a polymer which blocks the vast majority of incoming light but allows you to see the Sun and pretty much nothing other than the Sun.

That's how they work. But what we should be asking is why do we trust that they work?

And for most people it's simple. Somebody you trust told you that it's safe, maybe a parent, a coworker, somebody on the news, an astronomer, somebody on the Internet, and you believe them.

But for those of us for whom that is not enough, there is an additional assurance provided by the ISO.

This is the International Organization of Standardization, and it's a group of folks from all over the world who have come together to try to learn how to communicate better by agreeing on certain things.

My favorite standard of theirs is ISO 8601. This is the international standard for date formats, and it's the only format for writing dates that has ever made any sense to me.

Funny story. I once knew a guy who wrote dates some other way and he turned into a hat. So, you know, I'm not saying it's causation, I'm just saying, do you really want to take the risk?

We're not here to write dates, though. We're here to look at the Sun.

So that brings us to a different ISO standard, ISO 12312-2. And this is the safe solar viewing standard.

And the way that it works is that they list a uh-- a list of criteria, and if a material meets that criteria, it gets safety certified and people trust that it's safe.

Just so happens... these eclipse glasses are safety certified. They have it printed right there. So what we need to do is we need to dig into that standard and we need to understand the specifications that allow this to work.

And when we do, we get a mixture of letters and numbers. It's all very confusing. But if you put the letters and numbers together, we find something really quite fascinating.

We see the maximum amount of light allowed to transmit through the material and still be safety certified.

That's right. This is our threshold. It's the brightest thing you can look at safely, according to the ISO, at least.

Now, how did they come up with whatever this number is? My understanding is that they just uh, they just analyzed shade 12 welding glass.

Which, you know, fair enough. It's been used for a long time. It's uncomfortably bright, but not dangerously bright. So I think that's a fair enough approximation for me.

Now, what did they find with this? Well, they found that it allowed 0.0032% of light to pass through.

I presume this is mostly calibrated for the Sun. So if you look at something brighter than the Sun, these are not going to cut it.

It's also specified that this is a measurement of the visible spectrum of light. So caveat there.

Now, what do we do with this percentage? Well, thanks to the aforementioned smarty-scientist types, we can remember that the Sun has a stellar luminosity of 3.83 times ten to the 26 watts. Well, if we take our safe solar viewing percentage of this output, we get 1.23 times ten to the 22nd watts.

This is the stellar luminosity of a hypothetical star. Let's call it Batai.

So that's how bright Batai is. And if Batai were in place of the Sun and all other variables were identical, in theory, we could just just look at Batai all day. However long we want with the unaided eye and be totally fine. It would be perfectly safe.

Now, how bright is Batai really? It's--I mean, all stars are bright, right? So it's bright, but it's really on like, the bottom, bottom low end of what stars can be as far as brightness. This is brown dwarf brightness territory.

For context, do you remember Proxima Centauri? Which we mentioned earlier, it is the nearest neighbor to the Sun. It's a red dwarf star that we can't see unless we use telescopes.

Proxima Centauri is 60 times brighter than Batai. So what can we do with Batai? This little dim star.

Well, because we have its stellar luminosity and we have a distance by which we want to view it, we can derive an apparent magnitude. And with that we get -15.49, not -25. Okay?

Something that is -25 magnitude would be over 6,000 times brighter than Batai. So... very different conclusion there.

I think that's basically all we're going to get with Batai because we need the Sun. We're trying to look at the Sun. So what can we do-- What can we do with this apparent magnitude, which is now like the brightest thing we can look at in magnitude of form?

Well, because we have an apparent magnitude and we have the stellar luminosity of the Sun, we can derive a distance at which we see the Sun at that magnitude.

Now, you might want to prepare yourself. Okay? Take a couple of deep breaths in. Because I'm about to crack this wide open. I'm about to solve the mystery.

And the answer to that mystery is one hundred and seventy six AU.

Please, hold your applause until the end. You feel that feeling deep down? That's called gratification.

We had a problem and we found the answer. And that answer is a number.

What-- what does the number mean? That's a question you should always ask when it comes to outer space numbers, because they're all very abstract.

Well, immediately we can tell that 176 AU is much, much closer than our full moon estimate of 582 AU. And it feels way more plausible than our wiki estimate of 2.2 AU.

But, um... you know, realistically, this isn't even--176 is not like the actual real threshold. Remember, there are a lot of approximations and caveats.

Now, what is actually out there at 176 AU? There's not a lot. There's very-- there's very little.

There are a variety of scattered asteroids that nobody has ever heard of. That's the distance that Voyager One got by the year 2027.

Oh! And... of course, Sedna's out there. Sometimes. I'm not going to go check. I think I've learned my lesson. I'm staying here on Earth.

And by far the most impressive way to see the Sun from Earth is to use what's called a solar telescope. These are highly specialized pieces of equipment, and they produce just stunning views of the Sun.

They use filters and systems to isolate super, super narrow wavelengths of light. And depending on which wavelengths of light you're isolating, you can see different features and details in the Sun. Extraordinary.

So now let's say you don't have a solar telescope, but you do have a regular telescope and you don't have a solar filter to put on the front of it. Well, there is one additional technique you can use, and I really can't recommend it. It's maybe the most dangerous thing I have discussed today.

What you can do is you can line up the telescope with the Sun. You should always look at the shadow and not look at the Sun. That is how you line it up.

And once you've done so, it will project an image of the Sun out of the eyepiece. And there's a lot of great detail here. It's a nice, big, bright image.

But there are two major problems with this technique.

First, you might actually damage your telescope and nobody wants that.

Second, it might seem a little ridiculous, but you can actually forget that it is pointing at the Sun and you might look through the eyepiece at which point you bleach your retina. I've heard accounts of this and it sounds wildly unpleasant. It's the kind of mistake you don't make twice.

But pinhole cameras cost next to nothing and you can use those to look at the Sun as well. Not very detailed, but it gets the job done.

You can use your fingers or a colander. Or you can use leaves in a tree to make an improvised camera obscura projection.

This is probably most notable during eclipses because the shape of the Sun is so different that the projections look quite odd. But you can also use it to look at especially bright artificial lighting like I found with this bush and this LED strip.

But I've got a new favorite way to look at the Sun. It's called a Sun Spotter.

That's this thing! Wow. Look at this monolithic masterpiece, this gorgeous contraption.

But in order to see the Sun, we'll need to fully extend it out.

As you can see, it's this two lens projection system, and all you need to do is extend it out and line it up with the Sun.

Okay so the first lens collects more light than something like your eye would, and it focuses that image down into a very small but very bright point, maybe half a centimeter across.

The second lens is concave, though, so it projects the small, bright image into a much larger image of the sun against the back panel.

There are a few different ways that you can use this. You can sling it over your shoulder for a more handheld experience, which can be nice.

You're always looking away from the Sun, so it's perfectly safe and you can get a good view of the projected image this way. Earth rotates pretty quickly, so using this handheld lets you continually adjust to keep the Sun in alignment.

Or you can just set the whole thing down and prop it up. This gives you a really steady view of the Sun and it makes it super easy to lock in the focus.

And that's the Sun Spotter! I think it's really cool and I'm so pleased that it actually works.

Just look at that Sun. So big, so round.

Oh! Right. Uh, hmm.

I was so stricken by its luminous majesty that I completely forgot that I was looking for... Uh, I don't know.

I was looking for something. Whatever, I'm sure it's fine.

I guess that just goes to show that it doesn't necessarily matter what question you ask. There's always something to learn as long as you're diligent in your pursuit of that question.

Although, honestly-- the real lesson is probably don't look at the Sun.

Probably... Probably that--mostly, don't look at the Sun.

But every once in a while, don't.

Unless... don't.

EPILOGUE

You might be surprised to learn that a lot of information is held behind pay gates.

This includes things like the letter from Isaac Newton. You know, a historically significant document.

The ISO standard for solar viewing, research papers and so on.

I try to source free versions of these whenever possible, because I truly believe that information should be accessible. To that effect, this video was free to view.

However, if it gave you value and if you appreciate the uh-- the effort and if you have the means, consider supporting.

There are methods to do that listed in the description, including things such as direct support through Patreon and Bandcamp.

As always, thanks for your time.

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