<p>We'll need the angular diameter of the Sun: 31.6-32.7 arcminutes; the Moon's is between 29.3 and 34.1 arcminutes (found on Wikipedia).</p>

<p>The solar eclipse case is 0 degrees; it can only be an eclipse if the Moon is touching the Sun. In that case, their centers are at most (32.7 + 34.1) / 2 = 33.4 arcminutes apart.</p>

<p>A lunar eclipse would occur if the Sun and Moon are diametrically opposite in the sky; the separation of their centers is then 180 degrees. The actual separation is at least (31.6 + 29.3) / 2 = 30.45 arcminutes <em>less</em> than 180 degrees.</p>

CC BY-SA 4.0
2018-12-24T08:14:00.117Z
This is what I found in this code by a guy where he predicts solar eclipse by calculating the seperation between sun and moon: 
"if the separation between the Moon and the Sun is less than half of max sun
angular size + half of max moon angular size + half of earth angular size
seen from the moon: "(1952 arcseconds + 2046 arcseconds)/ 2 + (12742 / 3474)
* 2046 arcseconds / 2  in degrees"
Pranav Satheesh
CC BY-SA 4.0
2018-12-24T08:14:33.417Z
Why is he using  earth angular size
seen from the moon for this calculation? The results are more accurate if we include that.
Pranav Satheesh
CC BY-SA 4.0
2018-12-24T08:18:02.763Z
Because that answers *another* type of question: how far the Moon can be from the point diametrically opposite to the Sun during a lunar eclipse, or how far they can be apart during a solar eclipse *when viewed from the center of the Earth*; the eclipse itself may occur on the North or South pole. Then you have to take into account the size of the Earth as well.
Glorfindel
CC BY-SA 4.0
2018-12-24T08:19:07.417Z
Please consider asking this as a new question, rather than editing this one; edits which invalidate existing answers are [generally frowned upon](https://meta.stackexchange.com/q/286803/295232).
Glorfindel
CC BY-SA 4.0
2018-12-24T08:32:26.347Z
https://astronomy.stackexchange.com/questions/28856/what-should-be-the-seperation-between-sun-and-moon-during-a-solar-and-lunar-ecli
Pranav Satheesh
CC BY-SA 4.0
2018-12-21T13:08:05.890Z
2018-12-21T13:08:05.890Z
Glorfindel
<p>How do we calculate the maximum angular separation between sun and moon during:</p>

<ol>
<li>Solar Eclipse</li>
<li>Lunar Eclipse</li>
</ol>

CC BY-SA 4.0
2018-12-22T20:35:04.250Z
You might want to clarify that you're looking for any fractional eclipse, not totality.
Carl Witthoft
CC BY-SA 4.0
2018-12-24T08:15:21.770Z
Yes! For any fractional eclipse, not just totality.
Pranav Satheesh
<solar-eclipse><lunar-eclipse>
What is the maximum possible separation between sun and moon in the earth sky for an eclipse to occur?
Pranav Satheesh
# What is the maximum possible separation between sun and moon in the earth sky for an eclipse to occur?

(Asked by: username_0 on 2018-12-21)

How do we calculate the maximum angular separation between sun and moon during:

1. Solar Eclipse
2. Lunar Eclipse

**Tags:** solar-eclipse, lunar-eclipse
> **Comments:**
> **username_1**: You might want to clarify that you're looking for any fractional eclipse, not totality.  
> **username_0**: Yes! For any fractional eclipse, not just totality.  

---

## 1 answers

### Answer by username_2 on 2018-12-21. Score: 5

We'll need the angular diameter of the Sun: 31.6-32.7 arcminutes; the Moon's is between 29.3 and 34.1 arcminutes (found on Wikipedia).

The solar eclipse case is 0 degrees; it can only be an eclipse if the Moon is touching the Sun. In that case, their centers are at most (32.7 + 34.1) / 2 = 33.4 arcminutes apart.

A lunar eclipse would occur if the Sun and Moon are diametrically opposite in the sky; the separation of their centers is then 180 degrees. The actual separation is at least (31.6 + 29.3) / 2 = 30.45 arcminutes *less* than 180 degrees.

> **Comments:**
> **username_0**: This is what I found in this code by a guy where he predicts solar eclipse by calculating the seperation between sun and moon:  "if the separation between the Moon and the Sun is less than half of max sun angular size + half of max moon angular size + half of earth angular size seen from the moon: "(1952 arcseconds + 2046 arcseconds)/ 2 + (12742 / 3474) * 2046 arcseconds / 2  in degrees"  
> **username_0**: Why is he using  earth angular size seen from the moon for this calculation? The results are more accurate if we include that.  
> **username_2**: Because that answers *another* type of question: how far the Moon can be from the point diametrically opposite to the Sun during a lunar eclipse, or how far they can be apart during a solar eclipse *when viewed from the center of the Earth*; the eclipse itself may occur on the North or South pole. Then you have to take into account the size of the Earth as well.  
> **username_2**: Please consider asking this as a new question, rather than editing this one; edits which invalidate existing answers are [generally frowned upon](https://meta.stackexchange.com/q/286803/295232).  
> **username_0**: https://astronomy.stackexchange.com/questions/28856/what-should-be-the-seperation-between-sun-and-moon-during-a-solar-and-lunar-ecli  

---

