"Based on probability, the chances of any of us being here are vanishingly small."
THE DAILY ASTRONOMER
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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