Wikipedia:Reference desk/Archives/Science/2025 August 6

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August 6

Planetary Alignment question.

I remember being told by my science teacher (many years ago) that comments about entire solar system alignments were hogwash since the 9 planets (as I said years ago) couldn't all align within a certain number of degrees. First of all, does talking only about 8 planets made any difference and regardless, what are the planetary orbital resonances that keep this from happening and what is the minimum (for as far back/forward as we can make reasonable guesses).Naraht (talk) 01:41, 6 August 2025 (UTC)[reply]

Not much to do with resonances, a lot to do with the plane of each orbit. Greglocock (talk) 04:28, 6 August 2025 (UTC)[reply]

The orbital planes of the planets are inclined by only a few degrees with respect to the plane of the ecliptic. Unless prevented by resonances, they should in the very long run every now and then appear together on the celestial sphere within a few degrees of each other.  ​‑‑Lambiam 04:56, 6 August 2025 (UTC)[reply]

Here we find a claim that an alignment of all planets occurs on the average once every 180 trillion years. I cannot find the article presenting the calculations and do not know which definition it used for "lining up". And here we find the claim that on May 19, 2161, eight planets (apparently including Pluto) will be located within 69 degrees from each other.  ​‑‑Lambiam 11:49, 6 August 2025 (UTC)[reply]

See, for general background, Orbital resonance and particularly Orbital Resonance#Coincidental 'near' ratios of mean motion. {The poster formerly known as 87.81.230.195} 90.194.92.162 (talk) 16:37, 6 August 2025 (UTC)[reply]

Wow. Coincidental. Random on short timescales. I nominate you for the best reference ever. 41.246.129.161 (talk) 18:23, 6 August 2025 (UTC)[reply]

We have an article called planetary parade but it needs considerable beefing up. -- Jack of Oz ^{[pleasantries]} 19:34, 6 August 2025 (UTC)[reply]

• Planetary alignments might or might not be hogwash but they craziest thing about them is that they're so subjective and human-centric. This isn't the planets aligned radially in the solar system, something that might just have a system-wide effect. All it is are planets appearing to be in a line or close together, as viewed from Earth. Which looks impressive but isn't something the solar system is ever going to care about. 2A00:23C5:E9AC:DA01:BCF0:9806:F22E:E221 (talk) 15:38, 16 August 2025 (UTC)[reply]