THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
          "Based on probability, the chances of any of us being here are
vanishingly small."



THE DAILY ASTRONOMER
Wednesday, June 8, 2016
Aligning Planets

Yesterday's dip into the depths of Pandora's Jar brought us into the realm
of renegade planets: those Buddhist-like worlds that have managed to
maintain a perpetual state of non-attachment.     Today, we return to our
neighboring worlds as we address a most interesting question about aligning
planets.


*"Will the planets ever be in straight line, like we see them on your
planetarium mural?  What would we see if they were?"*


*-B. Davis, Cape Elizabeth*
Hello!
This is one of those times when we could offer a short, but correct answer
and leave it at that.  However, such curt responses are wholly unhelpful.
 The short answer is "no," one will never see the planets perfectly aligned
unless one visits a planetarium and stares at the wall.
Belgian astronomer Jean Meeus conducted a thought experiment in which he
assumed that the planets were in a straight line.   He then calculated how
much time would elapse until they were so aligned, again.    Meeus
determined that approximately 10,000,000,000,000,000,000,000 years would
have to pass before the would be "aligned" again.   Even in this
calculation, he permitted them to be within a degree of each other, and not
in a straight line.     That amount of time far exceeds the accepted age of
the Universe!      We can therefore assure you that the planets will never
be in a perfect line.

The problem pertains to the differences in orbital motions.  The closer
planets move faster than those farther away.   For instance, Mercury
completes one orbit about once every 88 days, whereas Pluto requires 248
years.  (Incidentally, Meeus did not include Pluto in his calculation.)
The planets move at different velocities. Moreover, they are also inclined
relative to the ecliptic, the plane defined by Earth's orbit.     Also,
planets affect each other, inducing perturbations that alter the orbits
slightly, but measurably.

There will be times when the planets will be within relatively small
sectors. Meeus found one example in which the planets -save Pluto- were
within a 40 degree sector.  This "gathering" occurred in the 13th
century.

Even three planets alignments on one side of the Sun are nearly
impossible.    We have experienced "close" alignments, such as in 1981 when
the oppositions of Jupiter and Saturn were a day apart (March 26 and March
27).     On those dates, someone observing the solar system from "above"
would have seen Earth, Jupiter and Saturn nearly in a line.


Now, after having gone through all that balderdash, let's pretend such an
alignment did occur.  What would we see?   Well, if the alignment were
perfect, we'd observe the simultaneous transit of Venus and Mercury across
the Sun.*   We'd watch Venus cross the Sun first, with Mercury initially
behind.   Then, at the precise time of the alignment,Venus would "occult"
Mercury, blocking it from view.    Then, as Mercury is faster, it would re
emerge during the transit.   (The next Venusian occultation of Mercury
won't happen until 2133 and that certainly won't happen during a transit.)

Meanwhile, we would see the mutual oppositions of the planets.  Mars would
transit Jupiter and Jupiter would occult the other planets at the precise
alignment.       Those watching the transits of Mercury and Venus would not
be able to observe the superior planets.

Honestly, as grand as such an alignment would be, the visuals wouldn't be
that spectacular...apart,  perhaps, from the simultaneous transits of the
inferior planets Mercury and Venus.



*We know of NO precisely simultaneous transits of Mercury and Venus.  It is
true that in 69,163 AD, Mercury and Venus will appear to be in transit at
the same time, but Venus won't be directly in front of Mercury.



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FROM THE CATACOMBS OF INFINITE KNOWLEDGE:

A transit occurs when the closer body appear smaller than the body with
which it is aligned.  When the close body is larger, the transit becomes an
"occultation," as the closer body completely blocks the more distant one.

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