Re: In the Shadow of the Moon

In article <vvqdnSkv975iz-7bnZ2dnUVZ_oCmnZ2d@xxxxxxxxxxx>,
Steve Vernon <stevezaxnospam@xxxxxxxxxxx> wrote:
If the Moon were to be moved to the "Earth-Sun L1 point" I don't know
if it would stay there. Doesn't the stability require M1>M2 and M2>>M3?
Is the moon small enough in mass to stay between the Earth and Sun?

The Moon's mass is only about 1/80th the mass of the Earth, so it's
negligible for many orbital-dynamics purposes. (For example, it's so
small and moves so fast that you can't get useful intuition about the
behavior of orbits in the Earth-Moon system by imagining that the Moon is
motionless -- just ignoring its effects entirely is more accurate than
ignoring its motion.)

*However*, an L1 point is not a stable parking place, regardless of mass.
(To be precise, as I recall, it is stable in two dimensions but unstable
in the third.) Objects can stay in its vicinity only with regular orbit
corrections -- not big corrections, if you do things right, but you do
need some.

The L4 and L5 points, aka "Trojan" points -- 60 degrees ahead of and
behind (e.g.) Earth in its orbit around the Sun -- *are* stable, if
perturbations from other bodies are negligible (not always a safe
assumption). But L1, L2, and L3, the "in-line" points, are not.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
.

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