# 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:** 10\ **Page:** 3
**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, 3:49pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/41 "2022-11-13T15:49:45Z")
There’s resolution, and then there’s resolution. You can’t tell anything about the shape of Jupiter by sight, and you couldn’t distinguish two points that close together from a single point, but you can visually tell that Jupiter isn’t a point source. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 13, 2022, 10:07pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/42 "2022-11-13T22:07:12Z")
> [@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. 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. 100% true, but there’s a bit more to it. I expect you already know what I’m about to mention but I wanted to add it for any other folks who’re less astronomical. As seen from Earth, the Moon is about 1/2 a degree = 30 arc-minutes in diameter. So half that in radius. If we ignore the small amount by which the other planets are not exactly on the ecliptic, we see the Moon can occult a planet any time the center of the Moon itself is within about +/- 15 arc-minutes of the ecliptic. By my definitely rough and ready calcs, that amounts to occultations being possible while the Moon’s celestial longitude is +/- 12 degrees of the moment of ecliptic crossing. Which corresponds roughly to +/- 12 clock hours of that moment. So out of the ~28 days of the Moon’s orbit, there are two ~1-day periods on opposite sides of the Moon’s orbit where planetary occultations are possible. I suspect you meant that by your choice of the word “regions” in “This means that there are two regions of the sky where a moon-planet occultation can occur.” But now we know (roughly) how big those regions are. Two days out of 28 is about 7%. ---
**Author:** ![JohnGalt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johngalt/32/184_2.png) [@JohnGalt](https://boards.straightdope.com/u/JohnGalt)\ **Post date:** [December 6, 2022, 2:05am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/43 "2022-12-06T02:05:23Z")
I want to bump this thread with a reminder about the [Lunar occultation of Mars](https://in-the-sky.org/news.php?id=20221208_16_100) on December 7th. It’s visible across much of the US, and it won’t be late at night. If it’s not cloudy I hope to get my granddaughter outside to see it; it’ll be about 9:30 pm here when it starts. When I told her about it, she said “But the moon doesn’t move!” This will be a good chance for her to see that it DOES move, just slowly. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [December 6, 2022, 3:28am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/44 "2022-12-06T03:28:25Z")
Depends what you count as “slowly”. If you think about it, if the moon takes 27.3 days to orbit the Earth, that works out to an average of 13.2 degrees per day, which means roughly half a degree, or its own diameter, each hour. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 6, 2022, 4:30am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/45 "2022-12-06T04:30:48Z")
Its diameter is about 2,200 miles. So it’s moving very roughly 2200mph along it’s orbit. Not so slow. It’s easy to watch the Moon move as long as you’ve got a decent line of sight to the horizon as it’s rising or setting. Kinf of like watching a snail, the progress is slow, but unmistakable. ---
**Author:** ![JohnGalt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johngalt/32/184_2.png) [@JohnGalt](https://boards.straightdope.com/u/JohnGalt)\ **Post date:** [December 6, 2022, 4:45am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/46 "2022-12-06T04:45:48Z")
The start and stop times of these Mars occultation are about an hour apart. So I can explain to my granddaughter that the moon moves about the distance of its own diameter each hour; it’s one thing to read that but another thing to actually see it happen in real time. (Ignoring the minor movement of Mars.) If she doesn’t think that’s pretty cool, at least I do. ---
**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:** [December 6, 2022, 11:58am UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/47 "2022-12-06T11:58:32Z")
> [@LSLGuy](#): > > It’s easy to watch the Moon move as long as you’ve got a decent line of sight to the horizon as it’s rising or setting. Kinf of like watching a snail, the progress is slow, but unmistakable. Are you referring to its movement relative to the horizon, or relative to the background stars and distant planets? In this thread we’re mostly talking about the latter, not the former. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [December 6, 2022, 12:14pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/48 "2022-12-06T12:14:23Z")
> [@JohnGalt](#): > > I want to bump this thread with a reminder about the [Lunar occultation of Mars](https://in-the-sky.org/news.php?id=20221208_16_100) on December 7th. It’s visible across much of the US, and it won’t be late at night. We went for a walk last night, and I looked at the relative positions of Jupiter, the Moon, and Mars, and mentioned to my wife that there’d be a conjunction of the latter two in a few days and possibly even an occultation. So I was right. Unfortunately, here on the North Shore of Boston is just outside the viewing area for the occultation, and even if I wanted to watch the close conjunction, it’s expected to rain all day tomorrow. 😠 ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [December 6, 2022, 12:24pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/49 "2022-12-06T12:24:19Z")
> [@Si\_Amigo](#): > > When planets are blocked from view on Earth by the moon its called a lunur occulation. Interesting, and a question that has never even occurred to me! ---
**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:** [December 6, 2022, 1:56pm UTC](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767/50 "2022-12-06T13:56:54Z")
> [@JohnGalt](#): > > I want to bump this thread with a reminder about the [Lunar occultation of Mars](https://in-the-sky.org/news.php?id=20221208_16_100) on December 7th. It’s visible across much of the US, and it won’t be late at night. Thanks JohnGalt. I’ll be ideally located for this, but it’ll be 5-6am for me, which would be perfect for ruining work that day. Still, could be great for people watching it if the Northern Lights are out at the same time. [Previous page](https://boards.straightdope.com/t/are-eclipses-of-planets-by-the-moon-a-thing/974767.md?page=2)