<p>After watching a <a href="https://www.youtube.com/watch?v=7wZKAoUeGRw" rel="nofollow noreferrer">Smarter Every Day 2 YouTube video</a> featuring Gordon Telepun, I purchased his ebook <a href="https://play.google.com/store/books/details/Gordon_Telepun_Eclipse_Day_2024_and_More?id=YCBnEAAAQBAJ" rel="nofollow noreferrer"><em>Eclipse Day 2024 and More</em></a> off the Google Play store. In the book, he has a link to <a href="http://xjubier.free.fr/en/site_pages/SolarEclipsesGoogleMaps.html" rel="nofollow noreferrer">Xavier Jubier’s website of solar eclipse maps</a>. On that site, he has every total and hybrid eclipse between 20 June 1955 and 15 December 2039 mapped onto Google Maps. The part that is confusing me is that there are two different measurements for magnitude and moon/sun ratio. My understanding is that the magnitude is the amount of the sun covered by the moon. So, a magnitude of 1.00945 means the moon is 0.945% bigger than the sun. So, that is the ratio of the moon’s size to the sun, right? Then, how does “Moon/Sun size ratio” have a different measurement of 1.05500? That’s a 4.5… % increase. So, what is the difference between the two, and can one be calculated from the other, or is much more data needed?</p>
<p>Just to be clear, the question is ‘What is the difference between the “Magnitude at Maximum” and “Moon/Sun size ratio”’ on Xavier Jubier’s eclipse maps. Secondarily, I would like to know if knowing only the one data point of either magnitude or moon/sun ratio is sufficient to calculate the other, or if more complex methods are needed.</p>

CC BY-SA 4.0
2024-04-25T08:28:54.590Z
To calculate the eclipse magnitude, you need to know the angular distance between the two centres, as well as the angular size ratio.
PM 2Ring
CC BY-SA 4.0
2024-04-25T14:19:55.943Z
Perhaps it is as simple as magnitude is area, size is angular diameter, so magnitude is approx. square of size (with adjustments for off-center eclipses)
antlersoft
CC BY-SA 4.0
2024-04-25T16:28:13.397Z
Good question. At the northern or southern limit, the magnitude is given as 1.000. That makes sense because the Moon can't cover any more than the diameter of the Sun. At the centerline, I notice that (1-moon/sun ratio)/(1-magnitude) = 2.000. That is a clue, but not entirely sure what it means.  It may indicate how far the Moon's limb extends beyond the Sun's limb at the middle of the eclipse which would be half the difference in diameters.
JohnHoltz
CC BY-SA 4.0
2024-04-25T17:31:57.907Z
On the centerline, they are the same thing.  Just looks like he used the radius for one and the diameter for the other.  As you move away from the centerline, the magnitude will change and has the definition $ \frac{L_1 - \Delta}{L_1+L_2} $ where $\Delta$ is the distance from the centerline.  Other variables described here: https://www.celestialprogramming.com/eclipsesGeneratingBesselianElements/generatingBesselianPolynomials.html
Greg Miller
<the-sun><the-moon><solar-system><earth><solar-eclipse>
What is the difference between a solar eclipse's (a) magnitude and the (b) moon/sun size ratio?
Curious Layman
# What is the difference between a solar eclipse's (a) magnitude and the (b) moon/sun size ratio?

(Asked by: username_0 on 2024-04-25)

After watching a [Smarter Every Day 2 YouTube video](https://www.youtube.com/watch?v=7wZKAoUeGRw) featuring Gordon Telepun, I purchased his ebook [*Eclipse Day 2024 and More*](https://play.google.com/store/books/details/Gordon_Telepun_Eclipse_Day_2024_and_More?id=YCBnEAAAQBAJ) off the Google Play store. In the book, he has a link to [Xavier Jubier’s website of solar eclipse maps](http://xjubier.free.fr/en/site_pages/SolarEclipsesGoogleMaps.html). On that site, he has every total and hybrid eclipse between 20 June 1955 and 15 December 2039 mapped onto Google Maps. The part that is confusing me is that there are two different measurements for magnitude and moon/sun ratio. My understanding is that the magnitude is the amount of the sun covered by the moon. So, a magnitude of 1.00945 means the moon is 0.945% bigger than the sun. So, that is the ratio of the moon’s size to the sun, right? Then, how does “Moon/Sun size ratio” have a different measurement of 1.05500? That’s a 4.5… % increase. So, what is the difference between the two, and can one be calculated from the other, or is much more data needed?

Just to be clear, the question is ‘What is the difference between the “Magnitude at Maximum” and “Moon/Sun size ratio”’ on Xavier Jubier’s eclipse maps. Secondarily, I would like to know if knowing only the one data point of either magnitude or moon/sun ratio is sufficient to calculate the other, or if more complex methods are needed.

**Tags:** the-sun, the-moon, solar-system, earth, solar-eclipse

> **Comments:**
> **username_1**: To calculate the eclipse magnitude, you need to know the angular distance between the two centres, as well as the angular size ratio.  
> **username_2**: Perhaps it is as simple as magnitude is area, size is angular diameter, so magnitude is approx. square of size (with adjustments for off-center eclipses)  
> **username_3**: Good question. At the northern or southern limit, the magnitude is given as 1.000. That makes sense because the Moon can't cover any more than the diameter of the Sun. At the centerline, I notice that (1-moon/sun ratio)/(1-magnitude) = 2.000. That is a clue, but not entirely sure what it means.  It may indicate how far the Moon's limb extends beyond the Sun's limb at the middle of the eclipse which would be half the difference in diameters.  
> **username_4**: On the centerline, they are the same thing.  Just looks like he used the radius for one and the diameter for the other.  As you move away from the centerline, the magnitude will change and has the definition $ \frac{L_1 - \Delta}{L_1+L_2} $ where $\Delta$ is the distance from the centerline.  Other variables described here: https://www.celestialprogramming.com/eclipsesGeneratingBesselianElements/generatingBesselianPolynomials.html  

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## 0 answers

