<p>A supermoon does not occur every three or four months. There may be 2 or 3 consecutive supermoons (that is, separated by 1 month) that occur at about the same time each year.</p>

<p>If you ignore the precession of the Moon's orbit, then there is one time of the year when the Full Moon and perigee occur (point 1 in my diagram below). Two weeks later, the New Moon occurs near apogee (point 2). At any other time of the year, the Full Moon occurs at a different point in its orbit around the Earth, so it is farther from the Earth than at perigee. Six months later, the Full Moon is occurring at apogee (point 4), and no one cares about that!
<a href="https://i.sstatic.net/ie4dC.png" rel="noreferrer"><img src="https://i.sstatic.net/ie4dC.png" alt="Earth&#39;s &amp; Moon&#39;s orbit"></a> (not to scale!)</p>

<ol>
<li>Full Moon at perigee (closest to the Earth)</li>
<li>New Moon at apogee (farthest from the Earth)</li>
<li>New Moon at perigee</li>
<li>Full Moon at apogee</li>
</ol>

<p>The Wikipedia article on the <a href="https://en.wikipedia.org/wiki/Supermoon" rel="noreferrer">Supermoon</a> has a nice graphic showing the Full Moon and distance from the Earth. Depending on how close to the Earth the Moon needs to be to be "super", you can see that there is a "season" when the supermoon occurs. (I have copied the image here, and added a dashed line at 360,000 km to show which moons might be "super" and which ones are not.)
<a href="https://i.sstatic.net/cH8np.png" rel="noreferrer"><img src="https://i.sstatic.net/cH8np.png" alt="enter image description here"></a></p>

<p>Now, if only people would care about the Super First Quarter Moon. Then we would be celebrating on May 12, 2019! (Not really. That is farther than the 360,000 km criteria.)</p>

CC BY-SA 4.0
2019-03-21T17:28:44.317Z
With apsidal precession, the major axis of the Moon's orbit rotates every 8.85 years, making the mean time between supermoon series about 13.53 calendar months. [Fred Espenak notes](http://astropixels.com/ephemeris/moon/fullperigee2001.html) that this is very close to 14 synodic months.
Mike G
CC BY-SA 4.0
2019-03-22T13:31:26.230Z
Does "supermoon" have a technical definition that allows us to say there can be 2 or 3 consecutive ones? Since it is practically impossible for the full moon to occur at _exactly_ the same instant as perigee, I assumed that the next most reasonable definition would be to call a full moon super if it occurs _nearer_ to earth than the previous and next full moons. But that would, by definition, not allow consecutive supermoons.
hmakholm left over Monica
CC BY-SA 4.0
2019-03-22T14:20:51.400Z
@MikeG - 13.94 lunar months by [my calculation](https://www.wolframalpha.com/input/?i=convert+1%2F(1%2F(365.2422+days)-1%2F(3231.6+days))+to+lunations).
David Hammen
CC BY-SA 4.0
2019-03-22T14:30:45.363Z
@HenningMakholm - The technical description is rather arbitrary. The difference between the Moon's apogee distance and the Earth-Moon distance at full moon has to be 90% or more of the difference between the Moon's apogee and perigee distances to qualify as a *supermoon*. It's worthy to note that this definition was developed and this term was coined by an astrologer rather than an astronomer. It's also worthy to note that due to variations in the Moon's eccentricity, some non-super full moons are more "super" than are some supermoons.
David Hammen
CC BY-SA 4.0
2019-03-22T14:50:56.110Z
@DavidHammen: The graph in the answer shows an annual variation in eccentricity, which looks like solar tides are deforming the moon's orbit. Are the 90% in percent of the _instantaneous_ apogee-perigee distance, or of difference between maximal and minimal distances over a period of several years? (The graph seems to suggest the latter).
hmakholm left over Monica
CC BY-SA 4.0
2019-03-22T19:18:46.253Z
@HenningMakholm - The added dashed line at 360000 km in the graph is erroneous. That is not the metric. For example, the full moon on 14 Oct 2008 was considered a supermoon at a distance of 367108 km and  the full moon on 10 Feb 2047 will be considered a supermoon at a distance of 367980 km. The perigee and apogee of interest are the two that occur closest in time to the full moon in question.
David Hammen
CC BY-SA 4.0
2019-03-22T19:55:14.903Z
According to the Wikipedia article, the 90% is based on the closest perigee and farthest apogee for the year, but some prefer to define the supermoon as when the Moon is closer than 359000 km (Sky & Telescope) or 360000 km (TimeandDate.com). I based my line on the latter. I did not check which dots in the chart for the full Moon are closer or farther than this distance, so I am not making any claims about March 2019 being a supermoon :-)
JohnHoltz
CC BY-SA 4.0
2019-03-21T14:34:24.763Z
2019-03-21T14:34:24.763Z
JohnHoltz
<p>Media coverage of the "super worm equinox moon" (*eyeroll*) has stated that this is the last supermoon of 2019.  Since supermoons normally happen every three or four months, how can there be big gaps?</p>

<p>It feels like phenomena like supermoons, which are basically due to the relative phase of orbits, shouldn't have sharp transitions like this.</p>

CC BY-SA 4.0
2019-03-21T15:44:03.537Z
That's no superMoon!
Carl Witthoft
CC BY-SA 4.0
2019-03-22T04:38:36.003Z
Maybe what you heard is that we get three or four of them per year? Although actually, I think its more like 2 or 3.
Octopus
CC BY-SA 4.0
2019-03-22T05:10:36.710Z
Have you no respect for a hallowed astronomical institution? The name "Super Worm Equinox Moon" is a proper noun, and as such should be capitalized! ;-)
uhoh
CC BY-SA 4.0
2019-03-22T09:39:02.167Z
@uhoh Guilty, your honour.
David Richerby
CC BY-SA 4.0
2019-03-22T09:43:49.327Z
@Octopus I probably heard three or four a year but it feels like they're in the news every few months, rather than a season of them each year. But that's probably my mistaken assumption that they're evenly spaced and my mistaken memory of the media coverage reinforcing each other.
David Richerby
CC BY-SA 4.0
2019-03-22T16:08:17.947Z
@uhoh, it's not a proper noun, it was probably capitalized in the title of an article, but it's just a bunch of adjectives and a noun.
Octopus
CC BY-SA 4.0
2019-03-22T16:33:18.850Z
@Octopus so the [Very Large Array](https://en.wikipedia.org/wiki/Very_Large_Array), the [Extremely Large Telescope](https://en.wikipedia.org/wiki/Extremely_Large_Telescope) and the [Large Hadron Collider](https://en.wikipedia.org/wiki/Large_Hadron_Collider) shouldn't be capitalized either? They seem to meet the same criterion of "just a bunch of adjectives" more or less ;-)
uhoh
CC BY-SA 4.0
2019-03-22T17:28:50.753Z
@uhoh, those are unique items (one and only one) with proper nouns for names. There is more than one super worm equinox moon. they occur every 19 or 20 years. There are several extremely large telescopes, so it is not necessarily a proper noun unless you are talking about the Extremely Large Telescope in Chile.
Octopus
CC BY-SA 4.0
2019-03-22T22:27:09.260Z
@Octopus [All US public holidays](https://en.wikipedia.org/wiki/Public_holidays_in_the_United_States) are capitalized, *and they come every year.* They are not unique, they are also names for cyclically appearing events just like our famous friend Super Worm Equinox Moon; e.g. Independence Day, Mother's Day, Halloween, New Year's Day, New Year's Eve, etc...That said, I just want to double check that we all understand that I was being satirical in my [original comment](https://astronomy.stackexchange.com/questions/30080/how-is-this-the-last-supermoon-of-2019?noredirect=1#comment54972_30080).
uhoh
<the-moon>
How is this the last supermoon of 2019?
David Richerby
# How is this the last supermoon of 2019?

(Asked by: username_0 on 2019-03-21)

Media coverage of the "super worm equinox moon" (\*eyeroll\*) has stated that this is the last supermoon of 2019. Since supermoons normally happen every three or four months, how can there be big gaps?

It feels like phenomena like supermoons, which are basically due to the relative phase of orbits, shouldn't have sharp transitions like this.

**Tags:** the-moon
> **Comments:**
> **username_1**: That's no superMoon!  
> **username_2**: Maybe what you heard is that we get three or four of them per year? Although actually, I think its more like 2 or 3.  
> **username_3**: Have you no respect for a hallowed astronomical institution? The name "Super Worm Equinox Moon" is a proper noun, and as such should be capitalized! ;-)  
> **username_0**: @uhoh Guilty, your honour.  
> **username_0**: @Octopus I probably heard three or four a year but it feels like they're in the news every few months, rather than a season of them each year. But that's probably my mistaken assumption that they're evenly spaced and my mistaken memory of the media coverage reinforcing each other.  
> **username_2**: @uhoh, it's not a proper noun, it was probably capitalized in the title of an article, but it's just a bunch of adjectives and a noun.  
> **username_3**: @Octopus so the [Very Large Array](https://en.wikipedia.org/wiki/Very_Large_Array), the [Extremely Large Telescope](https://en.wikipedia.org/wiki/Extremely_Large_Telescope) and the [Large Hadron Collider](https://en.wikipedia.org/wiki/Large_Hadron_Collider) shouldn't be capitalized either? They seem to meet the same criterion of "just a bunch of adjectives" more or less ;-)  
> **username_2**: @uhoh, those are unique items (one and only one) with proper nouns for names. There is more than one super worm equinox moon. they occur every 19 or 20 years. There are several extremely large telescopes, so it is not necessarily a proper noun unless you are talking about the Extremely Large Telescope in Chile.  
> **username_3**: @Octopus [All US public holidays](https://en.wikipedia.org/wiki/Public_holidays_in_the_United_States) are capitalized, *and they come every year.* They are not unique, they are also names for cyclically appearing events just like our famous friend Super Worm Equinox Moon; e.g. Independence Day, Mother's Day, Halloween, New Year's Day, New Year's Eve, etc...That said, I just want to double check that we all understand that I was being satirical in my [original comment](https://astronomy.stackexchange.com/questions/30080/how-is-this-the-last-supermoon-of-2019?noredirect=1#comment54972_30080).  

---

## 1 answers

### Answer by username_4 on 2019-03-21. Score: 11 | Accepted answer

A supermoon does not occur every three or four months. There may be 2 or 3 consecutive supermoons (that is, separated by 1 month) that occur at about the same time each year.

If you ignore the precession of the Moon's orbit, then there is one time of the year when the Full Moon and perigee occur (point 1 in my diagram below). Two weeks later, the New Moon occurs near apogee (point 2). At any other time of the year, the Full Moon occurs at a different point in its orbit around the Earth, so it is farther from the Earth than at perigee. Six months later, the Full Moon is occurring at apogee (point 4), and no one cares about that!
[![Earth's & Moon's orbit](https://i.sstatic.net/ie4dC.png)](https://i.sstatic.net/ie4dC.png) (not to scale!)

1. Full Moon at perigee (closest to the Earth)
2. New Moon at apogee (farthest from the Earth)
3. New Moon at perigee
4. Full Moon at apogee

The Wikipedia article on the [Supermoon](https://en.wikipedia.org/wiki/Supermoon) has a nice graphic showing the Full Moon and distance from the Earth. Depending on how close to the Earth the Moon needs to be to be "super", you can see that there is a "season" when the supermoon occurs. (I have copied the image here, and added a dashed line at 360,000 km to show which moons might be "super" and which ones are not.)
[![enter image description here](https://i.sstatic.net/cH8np.png)](https://i.sstatic.net/cH8np.png)

Now, if only people would care about the Super First Quarter Moon. Then we would be celebrating on May 12, 2019! (Not really. That is farther than the 360,000 km criteria.)

> **Comments:**
> **username_5**: With apsidal precession, the major axis of the Moon's orbit rotates every 8.85 years, making the mean time between supermoon series about 13.53 calendar months. [Fred Espenak notes](http://astropixels.com/ephemeris/moon/fullperigee2001.html) that this is very close to 14 synodic months.  
> **username_6**: Does "supermoon" have a technical definition that allows us to say there can be 2 or 3 consecutive ones? Since it is practically impossible for the full moon to occur at _exactly_ the same instant as perigee, I assumed that the next most reasonable definition would be to call a full moon super if it occurs _nearer_ to earth than the previous and next full moons. But that would, by definition, not allow consecutive supermoons.  
> **username_7**: @MikeG - 13.94 lunar months by [my calculation](https://www.wolframalpha.com/input/?i=convert+1%2F(1%2F(365.2422+days)-1%2F(3231.6+days))+to+lunations).  
> **username_7**: @HenningMakholm - The technical description is rather arbitrary. The difference between the Moon's apogee distance and the Earth-Moon distance at full moon has to be 90% or more of the difference between the Moon's apogee and perigee distances to qualify as a *supermoon*. It's worthy to note that this definition was developed and this term was coined by an astrologer rather than an astronomer. It's also worthy to note that due to variations in the Moon's eccentricity, some non-super full moons are more "super" than are some supermoons.  
> **username_6**: @DavidHammen: The graph in the answer shows an annual variation in eccentricity, which looks like solar tides are deforming the moon's orbit. Are the 90% in percent of the _instantaneous_ apogee-perigee distance, or of difference between maximal and minimal distances over a period of several years? (The graph seems to suggest the latter).  
> **username_7**: @HenningMakholm - The added dashed line at 360000 km in the graph is erroneous. That is not the metric. For example, the full moon on 14 Oct 2008 was considered a supermoon at a distance of 367108 km and  the full moon on 10 Feb 2047 will be considered a supermoon at a distance of 367980 km. The perigee and apogee of interest are the two that occur closest in time to the full moon in question.  
> **username_4**: According to the Wikipedia article, the 90% is based on the closest perigee and farthest apogee for the year, but some prefer to define the supermoon as when the Moon is closer than 359000 km (Sky & Telescope) or 360000 km (TimeandDate.com). I based my line on the latter. I did not check which dots in the chart for the full Moon are closer or farther than this distance, so I am not making any claims about March 2019 being a supermoon :-)  

---

