There’s been discussion among our learned commenters about a current alignment of planets and whether its tidal stress on Earth could have effects such as volcanism. So I thought I’d show where the planets are.
See the end note about enlarging illustrations.
In this space view, from a distance of 6 astronomical units (Sun-Earth distances) from the Sun at latitude 15° north of the ecliptic plane and longitude 120°, the courses of the planets are shown for the month of July, and there are sightlines to Uranus and Neptune because they are in a different direction.
The ecliptic heliocentric longitudes of the planets at July 21 are:
Mercury 349
Venus 328
Earth 299
Mars 328
Jupiter 293
Saturn 299
Uranus 38
Neptune 349
So, yes, some of the planets happen to be roughly on a spoke outward from the Sun.
The tidal force of body A on body B is the difference between its gravitational pull on the side of B nearer to it and on the side farther. That’s why there is a high tide on the side of Earth nearest to the Moon and also on the opposite side.
Let’s give some distances in kilometers.
The distance between the centers of Moon and Earth is 384,000 (average, approximate). The radius of Earth is 6,378. So the Moon’s distances to the near and far sides are 384,000-6,378 = 377,622, and 384,000+6,378 = 390,378. The difference between those is about 3 percent.
The distance of Jupiter from Earth is about 780,000,000,000. So the distances from Jupiter to the nearer and farther sides of Earth are 780,000,000,000 minus and plus 6,378. The difference between those is about 0.0016 percent.
There have been several planet-alignment scares. The Jupiter Effect (1974), by John Gribbin and Stephen Plagemann, predicted that a line-up on 1982 March 10 would cause catastrophes including a great earthquake on the San Andreas Fault.
There was some evidence that global tides may have been 40 micrometers (40 thousandths of a millimeter) higher than average. The only other part of the prediction that came true was that the book was a best-seller.
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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format. You may be able to enlarge them on your monitor. One way: right-click, and choose “View image”, then enlarge. Or choose “Copy image”, then put it on your desktop, then open it. On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers). Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.
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Apart from the sun and moon all the other planets have an almost insignificant effect on Earth although Jupiter is probably the reason that our orbit isn’t quite round like that of Venus but ever so slightly oval with Mars this is much more pronounced.the planetary alignment was handy for sending Voyager 2 out to visit all 4 outer planets whereas Pioneer’s 10/11 and Voyager 1 had only visited Jupiter and Saturn but not Uranus and Neptune.i have often wondered why Voyager 1 and 2 where not called Pioneer 12 and 13 and it seems that the deep space probes came from two different development lines; the Pioneer’s came from the Pioneer line and included more mundane inner solar system probes and the Voyager’s came from the Mariner line and Voyager 1 was originally called Mariner 11.
The planets do not have zero effect on planet Earth. We were talking about tidal force. The gravitational attractions of the other planets, deoending on their mass and distance, cause “perturbation” to the orbit of the Earth, and have to be built into the equations for the orbit. Indeed all the planet influence each other in this way.
You should take a look at the barycenter of each “insignificant” planet and also maybe consider their influence on the solar dynamo. The gas giants especially have a massive affect on Earth and alignments are major factors.
Thanks for once again putting a bit of realism in the “planetary alignment” notion that seems to repeatedly surface. I’ve found that taking folks on a “scale solar system” walk is the most effective way to drive home the infinitesimal effect of planets on each other.
With 8 major bodies, with most not playing a large gravitational role, continually orbiting the sun, alignments of some sort happen quite often.