Talk:Kordylewski cloud

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According to - Orbiting Solar Observatory 6 has been retired in 1972. How could it detect the clouds in 1975 ? //Skoot 01:30, 19 February 2006 (UTC)//


one of Larry Niven's novels mentions an astronautic mistake - I think as a contrived way of bringing the possible existence of these clouds out, presumably they had just been made mention of. Would a spacecraft be at significant risk if passing through the cloud, this was an asteroid mission oas I recall? Do the various space agencies carefully avoid them? Midgley 06:03, 16 March 2006 (UTC)

L4/5 stability[edit]

According to this article, L4 and L5 are unstable. According to the article on Lagrangian points, L4 and L5 are stable. Can someone clear this up? - Che Nuevara: Join the Revolution 21:08, 26 April 2006 (UTC)

You are right. It may be a mistake. See Lagrangian Point.

Albireo3000 23:45, 10 September 2006 (UTC)

It's correct. The L4 and L5 points of the Earth-Moon system are stable if you only take the Earth and Moon into account, but once you include the Sun they become unstable. The L4 and L5 points of the Sun-Jupiter system (where the Trojan asteroids are), for example, are far more stable, since there are no large objects to perturb them. --Tango 16:25, 7 May 2007 (UTC)

OSO 6 & cloud detection[edit]

The spacecraft was indeed retired in 1972. However, it's more than likely that people were working on the results of the mission for several years later. I looked for the report of Kordylewski's clouds in NASA's Technical Report Server ( & found:

Counterglow from the earth-moon libration points Roach, J. R. NASA Center for AeroSpace Information (CASI) 19750101; Jan 1, 1975 Results from the OSO-6 Rutgers Zodiacal Light Analyzer experiment show photometric perturbations above the background in the antisun line of sight. Sixteen successive lunations were examined, and the accumulated perturbations show a maximum value in the direction of the L4 and L5 earth-moon libration points. This is interpreted as a counterglow from a cloud of particles at the libration points. The average brightness of these libration clouds is 20 S10 Vis. The average angular size of the libration clouds is approximately 6 degrees. Their position varies from one lunation to the next, within an ellipsoidal zone centered on the libration-point direction, with its semimajor axis, of approximately 6 degrees, nominally in the ecliptic and its semiminor axis, of approximately 2 degrees perpendicular to the ecliptic. The position of these clouds with respect to the Lagrangian L4 and L5 points is towards the moon in the northern summer and away from the moon in the northern winter. Accession ID: 75A22340 Document ID: 19750038268 No Digital Version Available - Go to Tips on Ordering Updated/Added to NTRS: 2004-11-03

It's possible that a university librarian could obtain a copy of the article.

As for the question of L4/L5 stability: I'm not a physicist, so I could be off here. The "Trojan" minor planets, which are the Jovian/Solar L4 & L5 companions, actually wander around the exact points in sort of horseshoe orbits. If you think of L4 & L5 as the centres of more or less stable regions, around which the minor planets wander, you'll get a better picture of the situation, at least as I've been given to understand.

"Stability" here refers to whether a certain Lagrange point are negative or positive potential wells with respect to objects that have a similar orbit as the secondary body in the "trojan configuration". A body in an unstable Lagrange point, L1, L2 or L3, will "fall off" the Lagrange point with an increasing velocity if deviating from its center – a body in a stable Lagrange point, L4 or L5 will be "pushed back" to the Lagrange point if deviating from its center, which generally means that it orbits the center of the Lagrange point – in practice a horseshoe orbit. Perturbations from other planets not in the Lagrange configuration may intermittently decrease the stability of the Lagrange point. Rursus dixit. (mbork3!) 15:41, 28 November 2010 (UTC)
The abstract is good enough. I inserted a link to it in the article. Rursus dixit. (mbork3!) 15:44, 28 November 2010 (UTC)