<p>The sun has an apparent diameter of about ½ a degree, so when its centre is ¼ degree below the horizon, it is no longer visible.</p>
<p>However, this is not the same time as when it would be ¼ degree below the horizon if there were no atmosphere, because the atmosphere bends the sun's light and it appears to be higher in the sky than it actually is. This effect is strongest at sunrise and sunset.  The amount of bending depends on the distribution of temperature layers in the atmosphere.  The light is usually bent by more than half a degree.  The result is that the calculated position of the sun has to be about 5/6 of a degree below the horizon before it appears to set.  And I say &quot;about&quot; because the amount of atmospheric bending is not constant.</p>
<p>Of course, in much of the world, the sun doesn't set below a horizontal surface like the ocean, but behind hills or trees.  The time of when the sun is no longer visible depends on the positions of the hills.  In a few places, such as on top of a mountain, the horizon is below the observer, and so the sun sets later.</p>
<p>I don't understand the second question.  The sky will start to get light well before sunrise. Shadows will form whenever there is a local source of light. It's just a matter of how good your eyes are.</p>
<p>There is no fixed relationship between the colour of the sun and the time.  It depends on factors such as the presence of dust or smoke in the atmosphere.  Recently there have been some bright red sunsets in Britain, as a result of wild-fires in North America. At other times, sahara sand can cause red sunsets, and volcanoes can create dramatic sunsets world-wide.</p>

CC BY-SA 4.0
2024-09-11T21:20:19.153Z
For the last question about the color of the Sun: what you said is correct, but there are some standard models for typical circumstances.  I am not too familiar with any, but I'd point anyone interested to the source code for open source planetarium software like Stellarium.
Greg Miller
CC BY-SA 4.0
2024-09-11T21:40:40.387Z
@James K Thank you for your answer, For the first question: I am working on a game that does not have hills or trees, so for me, 5/6 degrees is enough for the sun to disappear from view. However, I need to know at what height or degree it becomes completely dark and the sky turns entirely dark.

For the second question, I clarified it further in the question.

For the third question: I mean in natural conditions, for example, how the color temperature of sunlight increases from 2000K to 3500K between sunrise and the golden hour. Is this increase from sunrise to noon linear or quadratic?
Ahmed Dyaa
CC BY-SA 4.0
2024-09-12T01:33:15.830Z
Is the matter more complicated than the relationship between two values? In this case, are there equations to calculate the temperature of sunlight?
Ahmed Dyaa
CC BY-SA 4.0
2024-09-12T18:23:06.127Z
The sky is not a black body.  So it doesn't have a black body colour temperature.  It isn't the case that "sunset =2000K"
James K
CC BY-SA 4.0
2024-09-11T19:58:49.893Z
2024-09-11T19:58:49.893Z
James K
<ol>
<li><p>When or at what altitude does the sun completely disappear from view?</p>
</li>
<li><p>When does the effect of the sun on objects facing it begin, for example, the formation of shadows when sunlight hits objects? Does this start at sunrise and end at sunset, or does it occur at a fixed altitude degree and end at a fixed degree as well?</p>
</li>
</ol>
<p><strong>An example for clarification:</strong></p>
<p>The appearance of the shadow resulting from the collision of sunlight with objects after it's altitude was greater than 0 degree.
<a href="https://i.sstatic.net/Dbp1zs4E.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Dbp1zs4E.jpg" alt="The appearance of the shadow resulting from the collision of sunlight with objects after it's altitude was greater than 0 degree." /></a></p>
<p>There is no trace of the shadow resulting from the collision of sunlight with objects.
<a href="https://i.sstatic.net/eMhidPvI.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eMhidPvI.jpg" alt="There is no trace of the shadow resulting from the collision of sunlight with objects." /></a></p>
<p>At what altitude does shadow begin to appear under natural conditions?</p>
<ol start="3">
<li>Is there an accurate reference that explains the relationship between the change in the color temperature of sunlight and the time of day? For example, it equals 2000K at sunrise and sunset.</li>
</ol>

CC BY-SA 4.0
2024-09-11T22:09:26.670Z
For your second question, it's not an on/off situation, the shadows gradually fade when the sun starts to go below the horizon and are gone when the last part goes below the horizon.  That could be emulated by having the shadow color gradually change to match the non-shadowed color as the sun sets.
Greg Miller
CC BY-SA 4.0
2024-09-11T23:01:54.897Z
Yes, I can do that, but I need the values for the altitude degree or the time for the beginning of the fading or the appearance of the shadow until it completely disappears or appears so that I can Lerp the shadow strength between 0 and 1.
Ahmed Dyaa
CC BY-SA 4.0
2024-09-11T23:06:51.897Z
Related: https://en.wikipedia.org/wiki/Twilight & https://en.wikipedia.org/wiki/Atmospheric_refraction
PM 2Ring
CC BY-SA 4.0
2024-09-12T01:22:50.963Z
A shadow is cast by an object blocking light coming from a particular direction but not blocking equivalent light coming from other directions. This is obviously the case when any part of the Sun is even marginally above the horizon and its light is shining on the object, and the object isn't strongly lit by other sources of light (eg overhead floodlight). However, there may still be reflected light from the Sun even when it has small negative altitude, so there may still be a faint shadow, especially if there are no other light sources.
Chappo Hasn't Forgotten
<the-sun><light><sunrise><sunset>
Questions about sun (Disk, Shadow, Light color temperature)
Ahmed Dyaa
# Questions about sun (Disk, Shadow, Light color temperature)

(Asked by: username_0 on 2024-09-11)

1. When or at what altitude does the sun completely disappear from view?
2. When does the effect of the sun on objects facing it begin, for example, the formation of shadows when sunlight hits objects? Does this start at sunrise and end at sunset, or does it occur at a fixed altitude degree and end at a fixed degree as well?

**An example for clarification:**

The appearance of the shadow resulting from the collision of sunlight with objects after it's altitude was greater than 0 degree.
[![The appearance of the shadow resulting from the collision of sunlight with objects after it's altitude was greater than 0 degree.](https://i.sstatic.net/Dbp1zs4E.jpg)](https://i.sstatic.net/Dbp1zs4E.jpg)

There is no trace of the shadow resulting from the collision of sunlight with objects.
[![There is no trace of the shadow resulting from the collision of sunlight with objects.](https://i.sstatic.net/eMhidPvI.jpg)](https://i.sstatic.net/eMhidPvI.jpg)

At what altitude does shadow begin to appear under natural conditions?

3. Is there an accurate reference that explains the relationship between the change in the color temperature of sunlight and the time of day? For example, it equals 2000K at sunrise and sunset.

**Tags:** the-sun, light, sunrise, sunset
> **Comments:**
> **username_1**: For your second question, it's not an on/off situation, the shadows gradually fade when the sun starts to go below the horizon and are gone when the last part goes below the horizon.  That could be emulated by having the shadow color gradually change to match the non-shadowed color as the sun sets.  
> **username_0**: Yes, I can do that, but I need the values for the altitude degree or the time for the beginning of the fading or the appearance of the shadow until it completely disappears or appears so that I can Lerp the shadow strength between 0 and 1.  
> **username_2**: Related: https://en.wikipedia.org/wiki/Twilight & https://en.wikipedia.org/wiki/Atmospheric_refraction  
> **username_3**: A shadow is cast by an object blocking light coming from a particular direction but not blocking equivalent light coming from other directions. This is obviously the case when any part of the Sun is even marginally above the horizon and its light is shining on the object, and the object isn't strongly lit by other sources of light (eg overhead floodlight). However, there may still be reflected light from the Sun even when it has small negative altitude, so there may still be a faint shadow, especially if there are no other light sources.  

---

## 1 answers

### Answer by username_4 on 2024-09-11. Score: 2

The sun has an apparent diameter of about ½ a degree, so when its centre is ¼ degree below the horizon, it is no longer visible.

However, this is not the same time as when it would be ¼ degree below the horizon if there were no atmosphere, because the atmosphere bends the sun's light and it appears to be higher in the sky than it actually is. This effect is strongest at sunrise and sunset. The amount of bending depends on the distribution of temperature layers in the atmosphere. The light is usually bent by more than half a degree. The result is that the calculated position of the sun has to be about 5/6 of a degree below the horizon before it appears to set. And I say "about" because the amount of atmospheric bending is not constant.

Of course, in much of the world, the sun doesn't set below a horizontal surface like the ocean, but behind hills or trees. The time of when the sun is no longer visible depends on the positions of the hills. In a few places, such as on top of a mountain, the horizon is below the observer, and so the sun sets later.

I don't understand the second question. The sky will start to get light well before sunrise. Shadows will form whenever there is a local source of light. It's just a matter of how good your eyes are.

There is no fixed relationship between the colour of the sun and the time. It depends on factors such as the presence of dust or smoke in the atmosphere. Recently there have been some bright red sunsets in Britain, as a result of wild-fires in North America. At other times, sahara sand can cause red sunsets, and volcanoes can create dramatic sunsets world-wide.

> **Comments:**
> **username_1**: For the last question about the color of the Sun: what you said is correct, but there are some standard models for typical circumstances.  I am not too familiar with any, but I'd point anyone interested to the source code for open source planetarium software like Stellarium.  
> **username_0**: @James K Thank you for your answer, For the first question: I am working on a game that does not have hills or trees, so for me, 5/6 degrees is enough for the sun to disappear from view. However, I need to know at what height or degree it becomes completely dark and the sky turns entirely dark.  For the second question, I clarified it further in the question.  For the third question: I mean in natural conditions, for example, how the color temperature of sunlight increases from 2000K to 3500K between sunrise and the golden hour. Is this increase from sunrise to noon linear or quadratic?  
> **username_0**: Is the matter more complicated than the relationship between two values? In this case, are there equations to calculate the temperature of sunlight?  
> **username_4**: The sky is not a black body.  So it doesn't have a black body colour temperature.  It isn't the case that "sunset =2000K"  

---

