## Re: [guide-user] Kordylewsky clouds L4/L5 earth-moon?

Bill Gray Dec 29, 2016

On 2016-12-25 06:35, Jost Jahn Yahoo@... [guide-user] wrote:
> Hi,
>
> is there a way to show the L4/L5 points (with potential Kordylewski
> clouds) of earth/moon system in Guide?
>
> They are 60 degrees away from the moon.

Hi Jost,

Figuring out where the Kordylewski clouds are appears to be complicated.

The "60 degrees" approximation might work if the moon's orbit were
circular, or close to it. But with an eccentricity of 0.055, it
ought to range from (at least) a bit under 57 degrees to a bit over
63. If the clouds have a longitude of perigee that is very different
from that of the moon's, the range could be more like 54 to 66 degrees.

My first thought was that the clouds should be in the same orbit as
the moon, but 1/6 of an orbit away. That is to say, compute where
the moon was 27.321661 / 6 days (a sixth of a sidereal month) ago, or
in the future. That does assume they're in essentially the same orbit,
though, coming to perigee at the same point as the moon does.

We also have the issue of whether the clouds are in the plane of the
moon's orbit, or in the plane of the ecliptic. Or, perhaps, oscillating
somewhat around one of those planes. I've found various references to
the Kordylewski clouds, but nothing that really explains any of this.

It does seem as if it should be worth looking into. It's clear that the
clouds would be somewhat transient (presumably, a meteor kicks up dust from
the moon, some of it gets caught at L4 and L5, and the dust slowly leaks
away from those points). But I'm not clear as to _how_ transient. If they
exist over short time spans, where the dust leaks away after a year or so,
it seems to me that it might be worth looking on a frequent basis for them.
(Which might explain why Kordylewski and others saw them, and a lot of
other people haven't.)

-- Bill