The rays of the sun are parallel

[michel123456]

The rays of the sun that hit the planet Earth are parallel, we know that. Even ancient Greek Eratosthenes knew that because he used this particularity for measuring the Earth's radius.

Then the question arises: why at the sunset do we see the sun rays converging towards the sun? (it is a sequel of an old thread I cannot find back)

[Strange]

!

Moderator Note

Why is this in Speculations? Are you proposing some “theory” to explain this?

 

[michel123456]

I couldn't find a better place.

Of course there is an answer. It is not a theory.

 

[Strange]

!

Moderator Note

As this is about geometry/perspective, I will move it to Mathematics 

 

You might want to compare with the parallel road edges in your other thread about perspective. 

[michel123456]

It has been closed.

I was looking for a forum about Geometry.

The meaning is to show that we are so deeply inserted into geometry to the point we don't even take notice of it.

[swansont]

1 hour ago, michel123456 said:

The rays of the sun that hit the planet Earth are parallel, we know that.

We know this?

That would imply that the sun's intensity is constant with distance, rather than dropping off as 1/r^2

Do you have any physics to support this claim?

The fact of the matter is that the rays are divergent, but with a very small angle

Quote

why at the sunset do we see the sun rays converging towards the sun?

Train tracks are parallel. They appear to converge in the distance. It's perspective/geometry, as discussed recently in your other thread. The angular separation gets smaller with distance, while the linear separation is constant. 

[Strange]

25 minutes ago, michel123456 said:

It has been closed.

That doesn't stop you looking at the picture.

25 minutes ago, michel123456 said:

The meaning is to show that we are so deeply inserted into geometry to the point we don't even take notice of it.

Except we do. For example, we have had two threads in the last few days about perspective.

[michel123456]

 

26 minutes ago, swansont said:

We know this?

That would imply that the sun's intensity is constant with distance, rather than dropping off as 1/r^2

Do you have any physics to support this claim?

The fact of the matter is that the rays are divergent, but with a very small angle

 

The sun's intensity is irrelevant.

The rays would be divergent if the Sun was a point but the Sun is huge compared to the Earth. Since the Earth receives rays from the entire surface of the sun (not only from its center) in fact the surface of the Earth receives converging rays (the orange ones on the sketch below). But because the Sun is so far away (much more than in the sketch), the rays are considered reaching the surface in a parallel way.

The grey rays on the sketch are spread around the Sun through the universe and do not reach the Earth.

 

If you compare the sketch with the picture, you will see that what we are observing is exactly the contrary of what is happening.

Edited October 9, 2019 by michel123456

[Sensei]

23 minutes ago, michel123456 said:

If you compare the sketch with the picture, you will see that what we are observing is exactly the contrary of what is happening.

...first draw it at the right scale...

Sun has radius ~0.7 mln km

Distance from the Sun to the Earth is ~150 mln km

150 / 0.7 = ~214 x

Have 1920x1080 screen resolution?

1920 is width of the entire screen.

1920 / 214 = ~9 pixels.

Draw circle with 9 pixels radius on the leftmost coordinate at x=0... and less than 1 pixel on the rightmost coordinate at x=1919 will be the Earth..

23 minutes ago, michel123456 said:

The sun's intensity is irrelevant.

Nonsense.

Do you have classical lightbulb in room? It's obeying inverse-square law too. Swansont's comment was about inverse-square law.

Edited October 9, 2019 by Sensei

[Eise]

Because.

First: the rays of the sun arrive here nearly parallel. But if they would be parallel, they would perspectively converge to one point, as my picture shows.

So second: you interpret your own picture wrong: the rays you see coming from the sun are not spreading, they are nearly pointed at you, they just go over your head, left of you, in front of you etc. But they do not radiate perpendicular to the sun's surface.

34 minutes ago, michel123456 said:

If you compare the sketch with the picture, you will see that what we are observing is exactly the contrary of what is happening.

Your sketch is wrong. I drew a few examples of what really is going on:

 

But of course you do not see the light rays that miss the earth (in the end you can't see2 light if it doesn't enter your eyes).

And last but not least, if you look into the opposite direction of the sun, you also see the sun beams converge:

From here. It also explains it:

Quote

Crepuscular rays appear to converge on the sun, anticrepuscular or antisolar rays converge in the opposite direction and you must have your back to the sun or sunset point to see them. They appear to converge towards the antisolar point, the point on the sky sphere directly opposite the sun. Like crepuscular rays they are parallel shafts of sunlight from holes in the clouds and their apparently odd directions are a perspective effect. Think of a long straight road, it converges towards the horizon but turn around and it also converges to the opposite horizon.   Crepuscular and anticrepuscular rays behave in the same way. 

Anticrepuscular rays are not rare but they must be sought carefully. When ordinary crepuscular rays are visible, turn around and search for their opposite numbers.  More rarely, sunrays pass right across the sky.

With a fish eye objective:

You do as the people who thought the earth is in the middle of the solar system: we do not feel the turning of the earth, we see the sky turn around us, so everything is turning around us.

Edited October 9, 2019 by Eise

[michel123456]

16 minutes ago, Eise said:

Because.

First: the rays of the sun arrive here nearly parallel. But if they would be parallel, they would perspectively converge to one point, as my picture shows.

So second: you interpret your own picture wrong: the rays you see coming from the sun are not spreading, they are nearly pointed at you, they just go over your head, left of you, in front of you etc. But they do not radiate perpendicular to the sun's surface.

 

Of course they don't radiate perpendicular to the Sun's surface, that's why I draw the orange ones in my sketch. The rays we receive are the ones between the orange triangle.

16 minutes ago, Eise said:

 

 

Your sketch is wrong. I drew a few examples of what really is going on:

 

But of course you do not see the light rays that miss the earth (in the end you can't see2 light if it doesn't enter your eyes).

 

 

My sketch is not wrong. I don't see we are disagreeing anywhere. The grey rays in my sketch are indicative. As I said, we are receiving rays from the entire surface of the Sun.

16 minutes ago, Eise said:

 

 

And last but not least, if you look into the opposite direction of the sun, you also see the sun beams converge:

From here. It also explains it:

With a fish eye objective:

You do as the people who thought the earth is in the middle of the solar system: we do not feel the turning of the earth, we see the sky turn around us, so everything is turning around us.

Interesting, I have never observed something like that. Usually I see the sunset at one side and (almost) black sky on the other side. Like in your fish eye picture.

34 minutes ago, Sensei said:

...first draw it at the right scale...

Sun has radius ~0.7 mln km

Distance from the Sun to the Earth is ~150 mln km

150 / 0.7 = ~214 x

Have 1920x1080 screen resolution?

1920 is width of the entire screen.

1920 / 214 = ~9 pixels.

Draw circle with 9 pixels radius on the leftmost coordinate at x=0... and less than 1 pixel on the rightmost coordinate at x=1919 will be the Earth..

Nonsense.

Do you have classical lightbulb in room? It's obeying inverse-square law too. Swansont's comment was about inverse-square law.

Nonsense??

The discussion is about the direction of the rays, not about their intensity.

And if you can draw "less than 1 pixel" be my guest.

Edited October 9, 2019 by michel123456

[Strange]

13 minutes ago, michel123456 said:

Nonsense??

The discussion is about the direction of the rays, not about their intensity.

And the reason the intensity falls off with an inverse square law is because they are not parallel, as you claimed. So very relevant.

 

[michel123456]

1 minute ago, Strange said:

And the reason the intensity falls off with an inverse square law is because they are not parallel, as you claimed. So very relevant.

 

That requires an explanation.

 

[Strange]

7 minutes ago, michel123456 said:

That requires an explanation.

Really?

The rays of light are radiating in a sphere from the surface of the Sun. Therefore the area subtended grows as distance², therefore the intensity falls off as 1/distance². Therefore the rays are not parallel. 

The rays that arrive at your eye (if you were foolish enough to look at the sun) would include both converging and diverging rays, because of its finite size (as you get half right).

[Eise]

28 minutes ago, michel123456 said:

Of course they don't radiate perpendicular to the Sun's surface, that's why I draw the orange ones in my sketch. The rays we receive are the ones between the orange triangle.

You only react on half of my post. How do you explain the converging sunbeams opposite of the sun?

[michel123456]

27 minutes ago, Eise said:

You only react on half of my post. How do you explain the converging sunbeams opposite of the sun?

Maybe you looked early when I was editing. I posted:

Interesting, I have never observed something like that. Usually I see the sunset at one side and (almost) black sky on the other side. Like in your fish eye picture.

Editing again, I looked at your link where my display gives a better resolution of the fish eye. Again I have never observed anything like that.

30 minutes ago, Strange said:

Really?

The rays of light are radiating in a sphere from the surface of the Sun. Therefore the area subtended grows as distance², therefore the intensity falls off as 1/distance². Therefore the rays are not parallel. 

The rays that arrive at your eye (if you were foolish enough to look at the sun) would include both converging and diverging rays, because of its finite size (as you get half right).

But we are not talking about the rays that do not reach the Earth. And the fact that the intensity drops down is irrelevant. However I understand that the square law is a result of geometry. (surprisingly because the geometry is plane, 2d, while the sphere is 3d). So intuitively it should be a cube law, contrarily to what is happening. (edited because irrelevant)

Anyways I still hope that everybody (except 2 or 3 respected members of this Forum) consider that the sun rays that reach the Earth are parallel. As stated in Eise link: https://www.atoptics.co.uk/atoptics/anti1.htm

Quote

Like crepuscular rays they are parallel shafts of sunlight from holes in the clouds and their apparently odd directions are a perspective effect. Think of a long straight road, it converges towards the horizon but turn around and it also converges to the opposite horizon.   Crepuscular and anticrepuscular rays behave in the same way. 

 

Edited October 9, 2019 by michel123456

[swansont]

1 hour ago, michel123456 said:

 

The sun's intensity is irrelevant.

I didn't say there was a dependence on the intensity. I said there was a dependence on the spatial behavior (specifically, radial) of the intensity.

 

Quote

The rays would be divergent if the Sun was a point but the Sun is huge compared to the Earth. Since the Earth receives rays from the entire surface of the sun (not only from its center) in fact the surface of the Earth receives converging rays (the orange ones on the sketch below). But because the Sun is so far away (much more than in the sketch), the rays are considered reaching the surface in a parallel way.

The grey rays on the sketch are spread around the Sun through the universe and do not reach the Earth.

 

If you compare the sketch with the picture, you will see that what we are observing is exactly the contrary of what is happening.

Your sketch is not to scale (which is consistent with this whole charade; see Sensei's comment), but even so, your lines are not parallel, as you admit. So this cannot possibly be a defense of the claim that light rays are parallel.

We can treat the light as being parallel as a first-order approximation, but claiming that they are actually parallel is a stronger statement, and not true.

[Strange]

14 minutes ago, michel123456 said:

But we are not talking about the rays that do not reach the Earth.

Now that is irrelevant. Do you think that only the rays that don't reach the Earth follow an inverse square law?

15 minutes ago, michel123456 said:

edited because irrelevant

And wrong.

Quote

Anyways I still hope that everybody (except 2 or 3 respected members of this Forum) consider that the sun rays that reach the Earth are parallel.

Approximately, yes. Personally, I would not have objected to the use of the word, assuming that you meant more parallel than the crepuscular rays. That is why I referred you to the picture you posted that showed the parallel edges of the road diverging in the same way.

This seems to be another utterly pointless (but more interesting) thread about your inability to understand perspective.

[Eise]

46 minutes ago, michel123456 said:

My sketch is not wrong. I don't see we are disagreeing anywhere. The grey rays in my sketch are indicative. As I said, we are receiving rays from the entire surface of the Sun.

Yes, but they do not converge as you suggest. Therefor I drew my red arrows: from every point of the sun light is emitted and diverging.

48 minutes ago, michel123456 said:

Interesting, I have never observed something like that. Usually I see the sunset at one side and (almost) black sky on the other side. Like in your fish eye picture.

It is not my picture of course. But you see how the sunbeams seem to diverge from the sun, and then converge again at the opposite horizon? That is because the beams are nearly parallel.

[michel123456]

14 minutes ago, Eise said:

Yes, but they do not converge as you suggest. Therefor I drew my red arrows: from every point of the sun light is emitted and diverging.

 

Right, the rays are emitted and diverging. We all agree.

How are they received?

[Strange]

6 minutes ago, michel123456 said:

Right, the rays are emitted and diverging. We all agree.

How are they received?

Do you think they stop diverging?

[michel123456]

It is not a difficult question: How are they received?

[dimreepr]

25 minutes ago, michel123456 said:

It is not a difficult question: How are they received?

It's not a difficult answer, not in parallel.

Even a laser doesn't emit light parallelally...

 

[Eise]

36 minutes ago, michel123456 said:

It is not a difficult question: How are they received?

Nearly parallel. The rest is perspective, as in my picture with the grid.

Edited October 9, 2019 by Eise

[studiot]

2 hours ago, michel123456 said:

As I said, we are receiving rays from the entire surface of the Sun.

 

3 hours ago, michel123456 said:

The grey rays on the sketch are spread around the Sun through the universe and do not reach the Earth.

 

This is fun but a small niggle here.

How are these two statements consistent with each other?

 

As a matter of interest, current approximations have the waves of light leaving points on the surface of the Sun as spherically expanding waves, but by the time they have reached Earth, we model them as plane waves.

Plane waves have parallel rays, spherical waves do not.