<p>For a small region not far from the equator,
an <a href="https://en.wikipedia.org/wiki/Equirectangular_projection" rel="nofollow noreferrer">equirectangular projection</a> will do.
If you want celestial north to be up,
declination should increase from bottom to top,
and right ascension should increase from right to left.
To correct the aspect ratio, scale the RA axis by cos(dec).
Then the sun and moon are circles of the respective angular radii, without the RA scale factor.</p>

<p>In the equation for $z$, $\Delta$ is the declination of the sun, $\delta$ is the declination of the moon, and $a$ is the difference in their right ascensions.</p>

<p><img src="https://i.sstatic.net/j2Lh0.png" alt="visualization of partial solar eclipse"></p>

CC BY-SA 3.0
2016-07-12T01:28:30.497Z
2016-07-13T01:56:12.813Z
2016-07-13T01:56:12.813Z
Mike G
<p><a href="https://i.sstatic.net/FCUb8.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/FCUb8.png" alt="enter image description here"></a></p>

<p>In relation to the image above, although the topic relates to math, how can I visualise the situation described in the final equation presented, i.e., the declinations, ascensions, solar and lunar radii. A diagram would be of great help.</p>

CC BY-SA 3.0
2016-07-11T14:08:38.320Z
A solar eclipse happens when the point on Earth where you are, the center of the Moon, and the center of the Sun, fall on one straight line.  The equation is just saying "the angle between the sun/moon (from your point of view) has to be small".
Fattie
<solar-eclipse>
Solar Eclipse: How it occurs
Einstein the troll
# Solar Eclipse: How it occurs

(Asked by: username_0 on 2016-07-11)

[![enter image description here](https://i.sstatic.net/FCUb8.png)](https://i.sstatic.net/FCUb8.png)

In relation to the image above, although the topic relates to math, how can I visualise the situation described in the final equation presented, i.e., the declinations, ascensions, solar and lunar radii. A diagram would be of great help.

**Tags:** solar-eclipse
> **Comments:**
> **username_1**: A solar eclipse happens when the point on Earth where you are, the center of the Moon, and the center of the Sun, fall on one straight line.  The equation is just saying "the angle between the sun/moon (from your point of view) has to be small".  

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## 1 answers

### Answer by username_2 on 2016-07-12. Score: 0 | Accepted answer

For a small region not far from the equator,
an [equirectangular projection](https://en.wikipedia.org/wiki/Equirectangular_projection) will do.
If you want celestial north to be up,
declination should increase from bottom to top,
and right ascension should increase from right to left.
To correct the aspect ratio, scale the RA axis by cos(dec).
Then the sun and moon are circles of the respective angular radii, without the RA scale factor.

In the equation for $z$, $\Delta$ is the declination of the sun, $\delta$ is the declination of the moon, and $a$ is the difference in their right ascensions.

![visualization of partial solar eclipse](https://i.sstatic.net/j2Lh0.png)


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