# How's it possible that 70% of Earth receives sunlight simultaneously

• yohananregal
Welcome to PF. In summary, this article reports that nearly 70% of the Earth's surface is illuminated by the sun on July 8th UTC.f

#### yohananregal

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Hello, I am new here.
I am wondering, how is it possible for nearly 70% of the spherical Earth to be illuminated by the sun every July 8th? How can a sphere be illuminated beyond 50% with a single light source. How do we explain this?

Welcome to PF.

russ_watters
I am wondering, how is it possible for nearly 70% of the spherical Earth to be illuminated by the sun every July 8th?

It isn't possible. I think what you read is that 80% of the LAND AREA of the Earth is illuminated at a certain time on July 8th.

swampwiz, russ_watters and PeroK
Thank you so much.
This is a known phenomenon. My friend showed it to me. Every single news outlet reported on it. I did the math, of the 99% of Earth's population who receives sunlight every July 8th, if my math is correct, it ends up being 69.35% of Earth's surface. How is this possible?

It isn't possible. I think what you read is that 80% of the LAND AREA of the Earth is illuminated at a certain time on July 8th.
Hello, no, that is not correct. Nearly 70% of Earth's surface is illuminated with some degree of sunlight, every July 8th, UTC. That is a fact.

malawi_glenn
if my math is correct, it ends up being 69.35% of Earth's surface. How is this possible?
It's possible your maths is incorrect!

It isn't possible. I think what you read is that 80% of the LAND AREA of the Earth is illuminated at a certain time on July 8th.
Hello, you are incorrect. Can you help?

russ_watters
Hello, yes. If you look at Time and Date's map and do the math, it is 69.35% of Earth's surface. How is this possible?
Can you tell us exactly how you're arriving at this number?
Are you by any chance measuring the percentage of the area on that map that is illuminated vs dark?
Because if you're doing that, you need to be careful which of the four progressively darker contours you're measuring against.
The first one, i.e. the brightest part of the map, is the only one showing where the Sun is visible above the horizon. This is the one that is 50%* of the total area of the map, as one would expect on an illuminated sphere without an atmosphere.
The other three show various grades of twilight - this is where the Sun is below the horizon, so it doesn't shine directly onto any part of the Earth within those contours, but its light reaches the surface through a combination of diffraction and scattering in the atmosphere. In this way a sphere covered in an atmosphere-like medium can be illuminated more than 50% at any time (this is not specific to the 8th of July, but any day of the year). If you're measuring against those, you'll get more than 50%. But, again, in this case it is not direct sunlight.

*I'm not sure the map goes into that much detail, but even the first contour should cover a little over 50%, as the aforementioned diffraction (bending of light) makes the rising/setting Sun briefly visible above the horizon even though it is geometrically below it.

pinball1970, PeroK and russ_watters

Those sources do not have a 70% number anywhere.

PeroK and russ_watters
Can you tell us exactly how you're arriving at this number?
Are you by any chance measuring the percentage of the area on that map that is illuminated vs dark?
Because if you're doing that, you need to be careful which of the four progressively darker contours you're measuring against.
The first one, i.e. the brightest part of the map, is the only one showing where the Sun is visible above the horizon. This is the one that is 50%* of the total area of the map, as one would expect on an illuminated sphere without an atmosphere.
The other three show various grades of twilight - this is where the Sun is below the horizon, so it doesn't shine directly onto any part of the Earth within those contours, but its light reaches the surface through a combination of diffraction and scattering in the atmosphere. In this way a sphere covered in an atmosphere-like medium can be illuminated more than 50% at any time (this is not specific to the 8th of July, but any day of the year). If you're measuring against those, you'll get more than 50%. But, again, in this case it is not direct sunlight.

*I'm not sure the map goes into that much detail, but even the first contour should cover a little over 50%, as the aforementioned diffraction (bending of light) makes the rising/setting Sun briefly visible above the horizon even though it is geometrically below it.
Hello, I found the first article online.

I read time and date and several other sites. I traced the terminator lines onto a globe and the math works out. This is not what spherical trigonometry teaches in regards to the Heliocentric model. The model claims 50% illumination, including twilight zones, maybe a percentage or two more accounting for possible unpredictibly erratic atmospheric refraction.

But 19.35% more? How is this possible. This is kinda freaking me out.

including twilight zones
No, without the twilight zones. This is explained in the post you quoted.

Those sources do not have a 70% number anywhere.
Hello, Yes, I am aware of this. I had to do the math myself. I am asking for verification of that. Time and Date offers what they claim to be an accurate daylight map of that day and time. When I traced out the daylight, including the twilight zones, it came to just under 70% percent. This seems impossible. I can not find much info on this. But it has been widely reported.

No, without the twilight zones. This is explained in the post you quoted.
No, it doesn't. You clearly did not do the math. You are just making claims.

PeroK, weirdoguy and russ_watters
No, it doesn't. You clearly did not do the math. You are just making claims.
Before you do the math, you have to consider a few facts:

What does sunlight mean? The atmosphere reflects a portion of it so that we have light some minutes after sundown. Are your calculations based on the graphic you have shown us? In that case, your math is doomed to be wrong. There is no two-dimensional flat map of the earth. How did you measure areas? Have you taken the various possible projections into account?

You have to be careful with claims made in popular magazines. Their only purpose is to get you to read their advertisements. Facts are irrelevant.

glappkaeft and berkeman
No, it doesn't. You clearly did not do the math. You are just making claims.
I believe you that with the twilight zones it's 70%-ish. That's not the point. The point is, w/o the twilight zones, that map shows 50% illumination. Look:

It's the same area.

You don't get twilight zones without atmosphere. You get more than 50% from the indirect light only. It's all perfectly normal.

russ_watters, glappkaeft and fresh_42
Before I forget the main argument:

What makes the 8th of July different from any other day? Certainly nothing related to sunlight on earth. The only possibility is the different amount of land in sunlight and related to that the different number of people on land in sunlight. Whatever it is, it necessarily has to take something more into account than the sun and a sphere.

Yes, relatively small misunderstandings, repeatedly, coming from correct facts, in each step loosing details, ending up making little sense even when most inputs are true. The percentage of the Earth that experiences a astronomical twilight is a number I won't calculate before going to bed (soon) but it could be close to his number but doesn't fit the facts presented in the OP when using standard nomenclature.

Not using standard nomenclature is the best situation where you explain your thoughts in detail since no-one can "read" your thoughts.

Before you do the math, you have to consider a few facts:

What does sunlight mean? The atmosphere reflects a portion of it so that we have light some minutes after sundown. Are your calculations based on the graphic you have shown us? In that case, your math is doomed to be wrong. There is no two-dimensional flat map of the earth. How did you measure areas? Have you taken the various possible projections into account?

You have to be careful with claims made in popular magazines. Their only purpose is to get you to read their advertisements. Facts are irrelevant.
Hello, thank you.

I have considered all of those variables. The point remains. The math is, as far as I can tell, correct. I traced the lines onto a globe and did the math. Including all the twilight zones, I came up with 69.35% of Earth's surface to receive some degree of sunlight every July 8th. I understand my measurements could be off, even if I was off by as much as 1%, that still seems impossible. However the problem remains.

Refraction is an un-uniform, unpredictable yet necessary variable to reproduce what is claimed to be a predictable, annual event. How can this be? Weather resources such as time and date, and others definitively universally state that some approximation of: 136,350,000 million of 196,900,000 million square miles of Earth's surface, receive some degree of sunlight every July 8th. That is just under 70% of Earth's surface area.

Such light patterns, if due to refraction, certainly could not be predicted decades in advance. That would require some 38,001,700 mile sq. to be uniformly lit to some degree due to highly unpredictable variables that are also annual. I don't think you understand the question. I can not find any info on this at all, nor is anyone willing to double check my math. Why?

I have considered all of those variables.
Then show us how.
Refraction is an un-uniform, unpredictable yet necessary variable to reproduce what is claimed to be a predictable, annual event.
It is not unpredictable. Also show that.
Such light patterns, if due to refraction, certainly could not be predicted decades in advance.
It can be done by people who knows physics and computational science.

phinds, russ_watters and fresh_42
I believe you that with the twilight zones it's 70%-ish. That's not the point. The point is, w/o the twilight zones, that map shows 50% illumination. Look:
View attachment 313929
It's the same area.

You don't get twilight zones without atmosphere. You get more than 50% from the indirect light only. It's all perfectly normal.
Hello, Yes that is true, but then you also get less than 12 hour days. You are not understanding the issue.

I have considered all of the variables. The point remains. My math is, as far as I can tell, correct. I traced the lines onto a globe and did the math. Including all the twilight zones, I came up with 69.35% of Earth's surface to receive some degree of sunlight every July 8th. I understand my measurements could be off, even if I was off by as much as 1%, that still seems impossible. However the problem remains.

Refraction is an un-uniform, unpredictable yet necessary variable to reproduce what is claimed to be a predictable, annual event. How can this be? Weather resources such as time and date, and others definitively universally state that some approximation of: 136,350,000 million of 196,900,000 million square miles of Earth's surface, receive some degree of sunlight every July 8th. That is just under 70% of Earth's surface area.

Such light patterns, if due to refraction, certainly could not be predicted decades in advance. That would require some 38,001,700 mile sq. to be uniformly lit to some degree due to highly unpredictable variables that are also annual. I don't think you understand the question. I can not find any info on this at all, nor is anyone willing to double check my math. Why?

Then show us how.

It is not unpredictable. Also show that.

It can be done by people who knows physics and computational science.
May I ask, do you know how to calculate refraction?

I have considered all of the variables. The point remains. My math is, as far as I can tell, correct.
You really don't won't to learn do you? Communication is the FIRST step...

fresh_42 and russ_watters
May I ask, do you know how to calculate refraction?
Please be careful. Other posters here have been vetted for the most part, and are pretty good in the subject matter. The Mentors are watching your posts in this thread.

Please be careful. Other posters here have been vetted for the most part, and are pretty good in the subject matter. The Mentors are watching your posts in this thread.
May I ask, what that means, to be careful? I am asking people to double check my math. Would you be willing to do that?

I am asking people to double check my math. Would you be willing to do that?
Sure, I'm happy to check your math. Have you posted it already? Perhaps I've missed it. And it would help if you posted your math using LaTeX, if possible. There is a link below the Edit window "LaTeX Guide" to help with that. Thanks.

May I ask, what that means, to be careful?
You have been using an insulting tone in many of your posts so far. Please do not do that. Thank you.

May I ask, what that means, to be careful? I am asking people to double check my math. Would you be willing to do that?
Maybe you should show some math?

May I ask, what that means, to be careful? I am asking people to double check my math. Would you be willing to do that?
Maybe you should show some math?
Hello, I thank you for responding. I have shown some sources in this thread and provided all of my conclusions and methods. The math seems very simple to do. Would you be interested in double checking my work?