<p>The orbits of the Galilean satellites have a roughly 2° incline. </p>

<p>Based on their distance from Jupiter and on the radius of Jupiter, I computed the apparent diameter of Jupiter from these satellites. The apparent diameter of Jupiter from each of these satellites is 19°, 12°, 7.5° and 4.3° for Io, Europa, Ganymede and Callisto respectively. </p>

<p>Therefore, the Galilean satellites pass in the shadow of Jupiter once per orbit around Jupiter. This means that there are eclipses on a daily basis. </p>

<p>For satellites with a more inclined plane like Themisto and Himalia, eclipses will happen less often, perhaps every six years (half of a Jupiter revolution). </p>

CC BY-SA 4.0
2019-11-22T21:32:27.470Z
It's probably not too far off to say that every time a Galilean satellite goes behind Jupiter from our perspective, it's near a lunar eclipse for that satellite.
Barmar
CC BY-SA 4.0
2019-11-23T06:38:43.553Z
Thanks for these numbers, which touch on a related question that I have not posted.  I see pictures of the shadow of Io on Jupiter far more often than the shadow of any other body.  Is that because of orbital inclination?  Apparently not!
Anton Sherwood
CC BY-SA 4.0
2020-09-02T15:58:38.947Z
How to find the duration of Jovian lunar eclipses? For example, for Europa
Snack Exchange
CC BY-SA 4.0
2019-11-22T15:05:05.620Z
2020-02-07T10:51:13.570Z
2020-02-07T10:51:13.570Z
usernumber
<p>Every Galilean moon and inner moon go into lunar eclipse once per orbit.</p>

<p><strong>How often is there a lunar eclipse of the Jovian moons?</strong></p>

<p>I set up a little animation of the Galilean moons (I didn't include the <a href="https://en.wikipedia.org/wiki/Moons_of_Jupiter#Groups" rel="noreferrer">inner moons</a>), and made a few assumptions (negligible moon size, sun at infinity, perfectly circular orbits) and found that there is a lunar eclipse in the Jovian system just under 10% of the time.</p>

<p><a href="https://i.sstatic.net/mlh49.gif" rel="noreferrer"><img src="https://i.sstatic.net/mlh49.gif" alt="Animation of the galilean moons of Jupiter going into Jupiter&#39;s shadow"></a></p>

<p>Here's a bigger version of the second graph.
<a href="https://i.sstatic.net/1Y7Sj.png" rel="noreferrer"><img src="https://i.sstatic.net/1Y7Sj.png" alt="enter image description here"></a> </p>

CC BY-SA 4.0
2019-11-23T02:58:19.053Z
`+n!`Time is in hours?
uhoh
CC BY-SA 4.0
2019-11-23T04:19:24.823Z
@uhoh I didn't have a particular time unit in mind when I coded it, but it looks to be in days. Sorry about the poor quality animation, I had to severely sacrifice quality to get it under 2 mb.
Ingolifs
CC BY-SA 4.0
2019-11-23T19:16:48.340Z
If you count *every* moon, I imagine the answer is not far off from "constantly".
Hearth
CC BY-SA 4.0
2019-11-24T11:13:50.983Z
@Ingolifs: Awesome animation. I can host a better quality version, if you wish.
Eric Duminil
CC BY-SA 4.0
2019-11-25T00:47:48.803Z
@Hearth, including the innermost moons, a back of the envelope calculation finds that Metis, Adrastea, Amalthea and Thebe spend approx. 20%,19%,13% and 10% of their time in Jupiter's shadow respectively. There will be some overlap with each other and with the Galilean moons, so those percentages aren't strictly additive. Themisto and the outer moons of Jupiter are so far out, and have such high inclinations (typically $30^o$ to $50^o$) that they are basically never in Jupiter's shadow.
Ingolifs
CC BY-SA 4.0
2019-11-25T06:04:42.387Z
@uhoh didn't you see the animation? The units are in tenths of a second.
Aequitas
CC BY-SA 4.0
2019-11-25T09:06:13.427Z
@Aequitas the Galilean moons have periods between two days and two weeks, so while the units probably aren't hours, they are certainly not tenths of a second. This SE site is about the real world, not a video game, though games are discussed occasionally; [1](https://space.stackexchange.com/q/22834/12102), [2](https://space.stackexchange.com/q/38343/12102)
uhoh
CC BY-SA 4.0
2019-11-26T04:53:37.307Z
@uhoh I think Aequitas is making a joke, based on the rate of the animation
Ingolifs
CC BY-SA 4.0
2019-11-26T06:05:37.300Z
@Ingolifs oh, (smacking forehead with palm in dramatic fashion...)
uhoh
CC BY-SA 4.0
2019-11-26T09:16:00.530Z
It's ok. I only got it after 6 hours myself.
Ingolifs
CC BY-SA 4.0
2019-11-23T00:32:37.327Z
2019-11-23T00:40:44.613Z
2019-11-23T00:40:44.613Z
Ingolifs
<p>For the Earth-Moon system, the orbit of the Moon is at a slight incline compared to the plane of the ecliptic. This incline is enough for there to be eclipses roughly twice a year rather than every lunar month. </p>

<p>But Jupiter is much bigger, so its shadow is bigger also. So it seems more likely for a satellite to go into its shadow. How often does this happen?</p>

CC BY-SA 4.0
2019-11-22T15:55:29.177Z
MIght separate into "how often does each of the major Jovian moons go into eclipse"
Carl Witthoft
CC BY-SA 4.0
2019-11-23T00:01:36.403Z
related (and kind-of cool!) [When will the next series of mutual eclipses of Jupiter's moons begin?](https://astronomy.stackexchange.com/q/23477/7982) **tl;dr:** January through August of 2021
uhoh
CC BY-SA 4.0
2019-11-23T21:57:45.550Z
I suppose that also depends on where you draw the line between a moon and a random chunk of ice in one of the rings.
John Dvorak
<jupiter><eclipse-non-earth-related><galilean-moons>
How often are there lunar eclipses on Jupiter
usernumber
# How often are there lunar eclipses on Jupiter

(Asked by: username_0 on 2019-11-22)

For the Earth-Moon system, the orbit of the Moon is at a slight incline compared to the plane of the ecliptic. This incline is enough for there to be eclipses roughly twice a year rather than every lunar month.

But Jupiter is much bigger, so its shadow is bigger also. So it seems more likely for a satellite to go into its shadow. How often does this happen?

**Tags:** jupiter, eclipse-non-earth-related, galilean-moons
> **Comments:**
> **username_1**: MIght separate into "how often does each of the major Jovian moons go into eclipse"  
> **username_2**: related (and kind-of cool!) [When will the next series of mutual eclipses of Jupiter's moons begin?](https://astronomy.stackexchange.com/q/23477/7982) **tl;dr:** January through August of 2021  
> **username_3**: I suppose that also depends on where you draw the line between a moon and a random chunk of ice in one of the rings.  

---

## 2 answers

### Answer by username_7 on 2019-11-23. Score: 19 | Accepted answer

Every Galilean moon and inner moon go into lunar eclipse once per orbit.

**How often is there a lunar eclipse of the Jovian moons?**

I set up a little animation of the Galilean moons (I didn't include the [inner moons](https://en.wikipedia.org/wiki/Moons_of_Jupiter#Groups)), and made a few assumptions (negligible moon size, sun at infinity, perfectly circular orbits) and found that there is a lunar eclipse in the Jovian system just under 10% of the time.

[![Animation of the galilean moons of Jupiter going into Jupiter's shadow](https://i.sstatic.net/mlh49.gif)](https://i.sstatic.net/mlh49.gif)

Here's a bigger version of the second graph.
[![enter image description here](https://i.sstatic.net/1Y7Sj.png)](https://i.sstatic.net/1Y7Sj.png)

> **Comments:**
> **username_2**: `+n!`Time is in hours?  
> **username_7**: @uhoh I didn't have a particular time unit in mind when I coded it, but it looks to be in days. Sorry about the poor quality animation, I had to severely sacrifice quality to get it under 2 mb.  
> **username_8**: If you count *every* moon, I imagine the answer is not far off from "constantly".  
> **username_9**: @Ingolifs: Awesome animation. I can host a better quality version, if you wish.  
> **username_7**: @Hearth, including the innermost moons, a back of the envelope calculation finds that Metis, Adrastea, Amalthea and Thebe spend approx. 20%,19%,13% and 10% of their time in Jupiter's shadow respectively. There will be some overlap with each other and with the Galilean moons, so those percentages aren't strictly additive. Themisto and the outer moons of Jupiter are so far out, and have such high inclinations (typically $30^o$ to $50^o$) that they are basically never in Jupiter's shadow.  
> **username_10**: @uhoh didn't you see the animation? The units are in tenths of a second.  
> **username_2**: @Aequitas the Galilean moons have periods between two days and two weeks, so while the units probably aren't hours, they are certainly not tenths of a second. This SE site is about the real world, not a video game, though games are discussed occasionally; [1](https://space.stackexchange.com/q/22834/12102), [2](https://space.stackexchange.com/q/38343/12102)  
> **username_7**: @uhoh I think Aequitas is making a joke, based on the rate of the animation  
> **username_2**: @Ingolifs oh, (smacking forehead with palm in dramatic fashion...)  
> **username_7**: It's ok. I only got it after 6 hours myself.  

---

### Answer by username_0 on 2019-11-22. Score: 15

The orbits of the Galilean satellites have a roughly 2° incline.

Based on their distance from Jupiter and on the radius of Jupiter, I computed the apparent diameter of Jupiter from these satellites. The apparent diameter of Jupiter from each of these satellites is 19°, 12°, 7.5° and 4.3° for Io, Europa, Ganymede and Callisto respectively.

Therefore, the Galilean satellites pass in the shadow of Jupiter once per orbit around Jupiter. This means that there are eclipses on a daily basis.

For satellites with a more inclined plane like Themisto and Himalia, eclipses will happen less often, perhaps every six years (half of a Jupiter revolution).

> **Comments:**
> **username_4**: It's probably not too far off to say that every time a Galilean satellite goes behind Jupiter from our perspective, it's near a lunar eclipse for that satellite.  
> **username_5**: Thanks for these numbers, which touch on a related question that I have not posted.  I see pictures of the shadow of Io on Jupiter far more often than the shadow of any other body.  Is that because of orbital inclination?  Apparently not!  
> **username_6**: How to find the duration of Jovian lunar eclipses? For example, for Europa  

---

