I chanced upon this in Stellarium.

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Is it common for five planet appear to align within 25°-30°, viewed from any of the inner planets?

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    $\begingroup$ I dont think that is a syzygy. A syzygy is when objects align in 3d space. That is an apparent alignment from the perspective of a viewer on mars, but not a true alignment. In particular the planets always appear aligned, since all orbit in the plane of the elliptic $\endgroup$
    – James K
    Commented Feb 22, 2020 at 19:19

1 Answer 1


It is not super-unlikely. Let's look at alignments of the three interior planets and two superior ones.

From Mars, the three interior planets (Earth Venus and Mercury) all appear to remain quite close to the sun, and so quite close to each other. Moreover they will seem to move slowly as they reach greatest elongation. The chance that two interior planets will be on the same side of the sun as each other is 50%, and they will be "close" quite often. I've not done careful calculations, but let's say there is a 1/3 chance that two interior planets are close.

So to get the third planet close is another 1/3 chance, it would have to be close to both other two planets but the probability of all three interior planets aligning somewhat is around 1/3^2 or roughly 10%. (This is a Fermi estimate so I'm taking the liberty of rounding)

Now the other planets can appear anywhere on the ecliptic. If you want them to be within 25 degrees of the others, that is a 25/360 chance (ie roughly 7%) and to get two planets both aligned is 7%×7% or about 0.5%. But there are four such planets, so six possible choices of two planets. That means that there is roughly a 3% chance that two superior planets will align with the inferior ones.

In conclusion, there is roughly a 0.3% chance of an alignment in the morning (or evening) sky on Mars. It is notable, but not super-unlikely. Your particular alignment includes Uranus (which is almost to faint to see) and Mercury (which is all but lost against the sun.) Close alignments of Jupiter Saturn Earth and Venus would look more spectacular. A similar four-planet alignment was visible on Earth a few years back. How to watch at best this week's planet alignement?

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    $\begingroup$ That it is notable is good enough for my purposes. Stellarium suggests that Mercury would appear 40 minutes before sunrise, and more than 11° above the horizon at sunrise. Would it be lost against the sun if that were the case? Maybe that is best for another question. $\endgroup$
    – Bob516
    Commented Feb 22, 2020 at 22:54

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