<p>The Moon does move 3.1&deg; in the 0.23 day difference between those month lengths, but it goes 360&deg; in a <em>sidereal</em> month and 363.1&deg; in an anomalistic month.</p>

<p>The anomalistic month, from perigee to perigee, is slightly longer because the <a href="https://en.wikipedia.org/wiki/Apsidal_precession" rel="noreferrer">perigee moves</a>.
The lunar apsides take 8.85 years to go all the way around the circle.</p>

<p>Similiarly, the draconic month is slightly shorter because the <a href="https://en.wikipedia.org/wiki/Nodal_precession" rel="noreferrer">nodes move</a> the other way in a cycle of 18.6 years.</p>

CC BY-SA 4.0
2020-04-18T02:14:19.090Z
2020-04-18T02:14:19.090Z
Mike G
<p>It's written everywhere that anomalistic month orbits <strong>360 degrees</strong> completely, then <em>how many degrees</em> does the sidereal month orbit?  </p>

<p><a href="http://hosting.astro.cornell.edu/academics/courses/astro201/sidereal.htm" rel="nofollow noreferrer">Here</a> is written that the sidereal month orbits 360 degrees too, but it doesn't make sense that they have the same orbit degrees since the anomalistic month is longer.</p>

<p>According to my logic, if 360 degrees equal to 27.55455 days, then 27.321661 days (=sidereal month) equal to 356.9 degrees, rather than 360 degrees. Is it correct? </p>

CC BY-SA 4.0
2020-04-19T11:58:11.017Z
Your logic is incorrect. Please accept @MikeG's answer as it is correct.
David Hammen
CC BY-SA 4.0
2020-04-19T12:28:31.510Z
No problem.  I'm just looking for reference who says it.  Once I find it,  I'll accept it.
Reckless Glacier
CC BY-SA 4.0
2020-04-19T12:56:08.900Z
Nowhere reputable is it written that in an anomalistic month the Moon orbits 360 degrees completely. **Nowhere**.
David Hammen
<sidereal-period>
How many degrees does the sidereal month orbit?
Reckless Glacier
# How many degrees does the sidereal month orbit?

(Asked by: username_0 on 2020-04-18)

It's written everywhere that anomalistic month orbits **360 degrees** completely, then *how many degrees* does the sidereal month orbit?

[Here](http://hosting.astro.cornell.edu/academics/courses/astro201/sidereal.htm) is written that the sidereal month orbits 360 degrees too, but it doesn't make sense that they have the same orbit degrees since the anomalistic month is longer.

According to my logic, if 360 degrees equal to 27.55455 days, then 27.321661 days (=sidereal month) equal to 356.9 degrees, rather than 360 degrees. Is it correct?

**Tags:** sidereal-period

> **Comments:**
> **username_1**: Your logic is incorrect. Please accept @MikeG's answer as it is correct.  
> **username_0**: No problem.  I'm just looking for reference who says it.  Once I find it,  I'll accept it.  
> **username_1**: Nowhere reputable is it written that in an anomalistic month the Moon orbits 360 degrees completely. **Nowhere**.  

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## 1 answers

### Answer by username_2 on 2020-04-18. Score: 7

The Moon does move 3.1° in the 0.23 day difference between those month lengths, but it goes 360° in a *sidereal* month and 363.1° in an anomalistic month.

The anomalistic month, from perigee to perigee, is slightly longer because the [perigee moves](https://en.wikipedia.org/wiki/Apsidal_precession).
The lunar apsides take 8.85 years to go all the way around the circle.

Similiarly, the draconic month is slightly shorter because the [nodes move](https://en.wikipedia.org/wiki/Nodal_precession) the other way in a cycle of 18.6 years.


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