# Are eclipses of planets by the moon a thing? **URL:** \ **Category:** Factual Questions\ **Created:** [November 11, 2022, 10:11pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767 "2022-11-11T22:11:21Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 11, 2022, 11:13pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/21 "2022-11-11T23:13:55Z")
> [@JohnGalt](#): > > The effect was that Venus suddenly blinked on, which was kind of amazing to me; I’m sure I said “Cool!” This is _exactly_ what I’m here for. I think with Jupiter, Saturn and Mars it might be even more exciting since the sky will generally be darker (though the moon will generally be fuller which might balance things out). ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 11, 2022, 11:14pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/22 "2022-11-11T23:14:31Z")
> [@k9bfriender](#): > > OTOH, unless you are looking through a telescope, Jupiter just looks like a really bright star, and you see stars going behind the moon all the time. Planets don’t look like stars. Mainly, they don’t twinkle as much as stars, because they aren’t point sources of light. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 11, 2022, 11:20pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/23 "2022-11-11T23:20:57Z")
> [@k9bfriender](#): > > I didn’t say that Jupiter wasn’t any brighter than a star, I said it looked like a really bright star. It really doesn’t though. I have a fairly good sense of where the ecliptic is much of the time, even when the moon isn’t visible. I can generally be quite confident if I see something really bright on that plane that it’s a planet, not a bright star like Sirius. Last week I saw Jupiter - I wasn’t sure which one it was initially but I was pretty confident it was one out of Saturn, Jupiter or Mars, and I was right. Tonight I saw Mars for the first time in months, and knew immediately what it was. Seeing the moon occulting one of the stars in the area of the ecliptic would be a lot less exciting. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 12, 2022, 3:21am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/24 "2022-11-12T03:21:35Z")
You can’t really mistake Jupiter or Venus for any other object in the sky. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [November 12, 2022, 3:45am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/25 "2022-11-12T03:45:35Z")
With a telescope or good binoculars, you can see something like this: > **[A Saturn-Moon Spectacle](https://skyandtelescope.org/observing/celestial-objects-to-watch/a-saturn-moon-spectacle/)** > > There will be other occultations of Saturn this year — but none with February's prime-time appeal for North American observers. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 12, 2022, 1:58pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/26 "2022-11-12T13:58:36Z")
> [@The\_Stafford\_Cripps](#): > > It really doesn’t though. I have a fairly good sense of where the ecliptic is much of the time, even when the moon isn’t visible. I can generally be quite confident if I see something really bright on that plane that it’s a planet, not a bright star like Sirius. We seem to be talking past each other somehow. I didn’t say you can’t identify it as a planet, or that it wasn’t on the plane of the ecliptic, or even that it twinkled. I said it looked like a really bright star, and that is true, it is a bright point of light in the sky. Before we knew what they were, we called them “wandering stars”, and we still do, because that’s what the word “planet” originally means. The point was that a bright point of light in the sky going behind the moon is not nearly as dramatic and noticeable as a lunar eclipse. Experiencing an eclipse in person is much different from seeing a picture or video of it. For an occultation, a video is going to be more or less the same as seeing it for yourself. > [@The\_Stafford\_Cripps](#): > > Last week I saw Jupiter - I wasn’t sure which one it was initially but I was pretty confident it was one out of Saturn, Jupiter or Mars, and I was right. Right, the planets are generally going to be more noticeable than stars, and they are on the plane of the ecliptic. If it’s in the dark night sky, it has to be one of those three. Now, one of the “benefits” of living in a highly light polluted place is that the planets are easy to identify since they are often just about the only things I can see in the sky. (I can barely make out the big dipper on a clear night.) > [@The\_Stafford\_Cripps](#): > > Seeing the moon occulting one of the stars in the area of the ecliptic would be a lot less exciting. I guess my perspective is that seeing Jupiter get occulted by the moon wouldn’t really be “exciting”. I wouldn’t bother to stay up much past my bedtime to see it, and I think my reaction would be, “Oh, neat.” Now, an occultation _during_ an eclipse, that may be more interesting. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 12, 2022, 2:16pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/27 "2022-11-12T14:16:26Z")
I dunno; an occultation might be less exciting than a solar eclipse, but I’d consider it much more so than a lunar eclipse. A lunar eclipse is gradual, due to the penumbra and the bloodshine. An occultation is sudden. As an aside, occultations of planets and stars by the Moon also offer a tremendous wealth of scientific data. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 12, 2022, 3:42pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/28 "2022-11-12T15:42:27Z")
> [@Chronos](#): > > A lunar eclipse is gradual, due to the penumbra and the bloodshine. An occultation is sudden. The eclipse starts off gradual, but when that last bit of light goes out, that’s sudden. It goes from the moon still casting shadows (though dimmed) to the moon just going out. I’d be interested in going out somewhere actually _dark_ to see one, as I think that would be even more dramatic, as in my area, there’s really not that much difference between a full and no moon. > [@Chronos](#): > > occultations of planets and stars by the Moon also offer a tremendous wealth of scientific data. Occultations by asteroids can give some useful information, but I’ve not heard of occultations by the moon having any particular scientific use. OTOH, during an eclipse, you can see impacts on the moon on the near side. Usually, a crescent or even new moon has too much Earthshine to see them. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [November 12, 2022, 9:26pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/29 "2022-11-12T21:26:17Z")
Try this link: As a subscriber, I get to share ten articles a month. > **[Three Planets Will Slide Behind the Moon in an Occultation (Published 2017)](https://www.nytimes.com/2017/09/17/science/occultation-moon-mars-venus-mercury.html?unlocked_article_code=Th_jWsQ0H7XZNN1vmbyiwUUDNR8xfK_lRN6o28wTTMNpxyW2VHEjLBn8qPIl1k6xLrdCihkfW0kTyZ3sUHfOWgbLEQAENZ37oSPvvh-rqJwQ6y0BHm49UfMSWhR6nRmExBXK2GooOV6B0PlT63UHxQyM2Z4CgDwjjKjGMI8HJHteTaSYVNZczIRxXRPV77EIU7ERe7tc5wCdSXA97VEpLmGcb8uh-mQHSRGCUttDLZOZ4JgPL03S1NKNcBboXkYdqX9TLgXLMhXOr42HWyVJMHtB0GQro4iMRLB5qbWjtfZoxg38QhfZ0Q9w1MAWRXnKUW_rlanUc7K_ZebeItmTcPdQooUUGo0hnnSaUH8&smid=share-url)** > > The moon will momentarily block Venus, then Mars and then Mercury, offering a vivid reminder of the cosmic clockwork of our solar system. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [November 12, 2022, 10:28pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/30 "2022-11-12T22:28:23Z")
Actually, just yesterday the website Astronomy Picture of the Day posted a very interesting picture of a [planet eclipsed by the moon](https://apod.nasa.gov/apod/ap221111.html). But there really isn’t that much to see in the big picture – it’s only in that expanded view that you can clearly see Uranus about to be eclipsed, even though it’s about 15 times bigger than the moon! ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 12, 2022, 11:36pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/31 "2022-11-12T23:36:59Z")
Unfortunately, Uranus isn’t visible to the naked eye\*, so unless you had a telescope, there wouldn’t have been much to see either. It may be 15 times bigger than the moon, but it’s a whole lot further away. \*It is just bright enough that it could theoretically be seen by someone with very good eyes on a very dark night, but it’s certainly no Jupiter. ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [November 12, 2022, 11:58pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/32 "2022-11-12T23:58:21Z")
> [@The\_Stafford\_Cripps](#): > > I notice that there don’t seem to be mentions of Saturn or Jupiter being occulted, which brings me back to the OP: does their plane or something mean that they only pass directly behind the moon twice in 43276 years or whatever? The moon’s orbit is tilted about 5 degrees to the ecliptic, which means that it’s only positioned to possibly occult a planet when the moon crosses the ecliptic (twice a month, at opposite sides of its orbit). This means that there are two regions of the sky where a moon-planet occultation can occur. Inner planets like Venus and Mars pass through those regions fairly often, and apparently Uranus is in one of them now. Jupiter and Saturn aren’t positioned to be occulted, and with their relatively long orbital periods years can go by before they are. EDIT: A quick search indicates a lunar occulation of Jupiter on 17 May 2023 and one of Saturn on 03 May 2024. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 13, 2022, 9:09am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/33 "2022-11-13T09:09:38Z")
> [@k9bfriender](#): > > I said it looked like a really bright star, and that is true, it is a bright point of light in the sky. It doesn’t. I weakened my point by mentioning the ecliptic, but there are no stars that look like what Jupiter and Mars do just now, no planets that look like Sirius. I’m not sure why you feel the need to keep saying that seeing a bright Jupiter obscured or reappearing behind a mostly dark moon would not be exciting, when the desire to see that is the whole point of my thread. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 13, 2022, 9:12am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/34 "2022-11-13T09:12:24Z")
> [@Hari\_Seldon](#): > > Try this link: As a subscriber, I get to share ten articles a month. Thank you, that was interesting. As I mentioned before, it hadn’t occurred to me that such occultations would be so localised. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 13, 2022, 9:15am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/35 "2022-11-13T09:15:36Z")
> [@k9bfriender](#): > > nfortunately, Uranus isn’t visible to the naked eye\*, so unless you had a telescope, there wouldn’t have been much to see either. I have tried to see Uranus with ordinary hand held binoculars, just for the sake of it. I think I probably did see it but in this case it was hard to distinguish from the faint stars in its neighbourhood, especially as it was difficult to somehow check the star map and then adjust my eyes again to the darkness. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [November 13, 2022, 9:24am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/36 "2022-11-13T09:24:39Z")
> [@Steve\_MB](#): > > EDIT: A quick search indicates a lunar occulation of Jupiter on 17 May 2023 and one of Saturn on 03 May 2024. Thanks. It looks like both planets will be close to the sun in the sky on those occasions and the Saturn one won’t be visible at all from where I am. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [November 13, 2022, 9:57am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/37 "2022-11-13T09:57:21Z")
> [@k9bfriender](#): > > Occultations by asteroids can give some useful information, but I’ve not heard of occultations by the moon having any particular scientific use. In the past the moon was the first step for calculating the absolute distances to the other planets by triangulation. The relative distance is easy to calculate from Kepler’s Laws, but the absolute had to go step by step, more or less as follows: assume the stars to be at an infinite distance from Earth. Taking them as background, calculate by triangulation he distance to the moon by observing an occultation from one point of the Earth and comparing it with the same simutaneous observation from as close to the antipodes as possible. Knowing the distance to the moon, calculate the distance to Venus: triangulate during an accultation. By Kepler’s Law, you now can calculate the distance to the other planets and the sun. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [November 13, 2022, 1:14pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/38 "2022-11-13T13:14:06Z")
Grazing occultations are another interesting one. The edge of the moon brushing past a star causes the star to wink in and out, and in principle can tell you something about the lunar terrain - as the star is shining through the valleys. In the modern day of extensive lunar mapping not such a big deal, but a cool concept. A zillion years ago a fellow lunatic and I went out to observe one such grazing occultation. Back then things were a bit primitive. I had my Celeston 8, and we drove out to where the occultation was predicted to occur. The location is very sensitive, much more so than a solar eclipse. Within a few hundred meters I think. To be of any interest the observation timing needed to be quite precise. The trick was to take a radio tuned into the time service and a tape recorder that would hear you as you called out the occultation and also heard the time signals. Sadly, we got all set up, and the clouds came over. So cold and disappointed we packed up and never bothered again, our attempt to aid in pushing back the barriers of science thwarted. Grazing occultations of the planets are perhaps a bit of fun as well. Again, very fine location dependence. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 13, 2022, 1:41pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/39 "2022-11-13T13:41:49Z")
> [@Steve\_MB](#): > > The moon’s orbit is tilted about 5 degrees to the ecliptic, which means that it’s only positioned to possibly occult a planet when the moon crosses the ecliptic (twice a month, at opposite sides of its orbit). This means that there are two regions of the sky where a moon-planet occultation can occur. True, but also those positions in the sky themselves shift over time, as the orbit of the Moon precesses. IIRC, that’s about a 19-year period. And occultations of stars can also tell you something about the angular size of the stars, since they don’t quite wink out all at once. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [November 13, 2022, 2:09pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/40 "2022-11-13T14:09:29Z")
> [@dtilque](#): > > Planets don’t look like stars. Mainly, they don’t twinkle as much as stars, because they aren’t point sources of light. True, but Jupiter extends [30 - 51 arc seconds](https://skycalendar.com/tutorial/angulardiameter.html). The minimum resolution of the Mk 1 eyeball for people with exceptional eyesight is 1 arc _minutes_ – 60 arc seconds; for most people it’s 3 arc minutes. There are reports of people being able to see [Venus as a crescent](https://en.wikipedia.org/wiki/Phases_of_Venus#Naked_eye_observations) because it extends as much as 66 seconds. Jupiter, though, is going to appear to be a point, albeit a non-twinkling one. [Previous page](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767.md?page=1) [Next page](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767.md?page=3)