The truth is, the planets in our solar system never actually line up perfectly. This is something that we think should happen because a lot of the artwork surrounding the solar system sees all of the planets in a perfectly straight line that is just not achievable for our solar system. We are led to believe that the planets all orbit the sun on the same line. But in reality, all of the planets are orbiting the sun along different three-dimensional lines that are not strictly perfect. For this reason alone, the planets will not line up.
Imagine a far full of fireflies on an evening. It is very unlikely that all of the fireflies will line up in an exact straight line. This is because they will all be flitting about along different paths within the three-dimensional jar.
They will not all follow a two-dimensional path. So, it is unusual then, that all of the drawings of the solar system show that the planets orbit the sun in the same line.
To add even more confusion to the mix, astronomers will often refer to something called ‘planetary alignment’. This, contradictory to the name, does not mean that the planets will all line up like alert soldiers.
They mean that some planets are in a similar region of the sky. This also almost never happens, especially with all of the planets at the same time. It is more likely to happen to two or three planets around the same time.
Another factor to consider is that this planetary alignment is fully dependent on the position of the viewing planet. Here on earth, we could be ‘aligned’ with two other planets in the sky. But this may only be from our point of view.
If an astronaut on Mars were to be told that the planets were aligned, they might look up to see no such thing. So, perspective is also important when it comes to the planets ‘aligning’.
So, the short answer to the question is that the planets do not all align. In fact, in space it is highly unlikely that things align in the way that the question suggests. But even if the planets did all line up, there would be no real effects on earth from the phenomenon. Again, we are led to believe that if anything aligns with earth, something bad is bound to happen.
This is thanks to a lot of science fiction films and conspiracy theories in general. Certain beliefs include that if the planets all align, the sun will shoot a beam of light through all of them… thankfully nothing like this is remotely true or even possible. A fun premise for a science fiction story though!
The reason the alignment of planets does not affect us on earth is because the gravitational pulls of the planets are too far away to interfere with us. The moon, as an astronomical body, does affect our tides, but that is because of its close proximity to earth. The sun is the only other astronomical body that influences us.
The sun is absolutely huge though, even though it is further away from us than some planets, its effect is still great. The sun’s gravity is responsible for out earth’s orbit and seasons and the hours in our day. As previously mentioned, the moon is responsible for the tides thanks to its gravitational pull.
Interestingly, the occasional alignment of the sun and moon with earth does actually have an effect on the earth. This produces something called a spring tide which, simply put, is a stronger tide every full moon. The ‘spring’ refers to the springy nature of the water when the tide comes in, since it appears stronger than other tide patterned in the month.
A perfect way to illustrate that a human being will not feel the effects of the gravity from other planets is to think about the numbers. If we take Newton’s Law of Universal Gravitation, as well as the known masses and distances of all of the astronomical bodies in our solar system, there a lot of calculations we can do:
If you are a person standing on the equator of earth and you weigh approximately 100kg, the earth’s gravitational force inn Newtons is 980. This is the strongest force of gravity that you would feel because you are standing on the earth’s surface and you are closest to the earth than any other astronomical body in the solar system.
Interestingly, when Jupiter, the biggest planet in our solar system, is closest to earth, only 0.000037N are experienced. This is absolutely miniscule compared to the force of earth.
And that is the closest that Jupiter can be to earth. So, if we imagine that all of the planets were the closest that they could possibly be to earth, and you were stood at the equator weighing 100kg, the gravitation force exerted would only be 0.000064N.
That is hardly any more than Jupiter alone. This just goes to show that the planets aligning would have no real noticeable effect on earth, or on the people who inhabit it.
This combined gravitational force of all of the planets when they are hypothetically all at the closest to earth, shows a value that is a whopping 53 times weaker than the gravitational force of the moon. And we don’t even really feel the effects of the moon’s gravity, we only see it in the tides.
If this combined gravitational force from the planets was going to affect us, then the moon’s gravitational force would have done some damage to us already at a level of 15 times worse. We do not see any increase in natural disasters when the full moon comes around, so it is obvious that the moon’s gravitational force is not strong enough to do any harm, so neither would the unlikely ‘alignment’ of the planets.
But you came here for a sold answer, as well as a fun one. So, I am pleased to tell you that there is a time in our future when the planets will become somewhat aligned. Obviously, we used the term ‘aligned’ loosely. But I am sorry to inform you that you will not be alive then, since it is in 2492. So, you may have to settle for seeing at most two planets in the sky.
But in 2492, on May 6, a huma being will be able to see a whopping eight planets in the sky at around 5:10am in New York. The that is every planet except earth visible in the sky. If you’ve read this answer properly, you will know that these planets will not be aligned in a straight line, and that planetary alignment simply means that they will all be in the same region of sky at the same time.
But this in itself is very impressive! Since it is very unlikely for things in space to align in anyway, the fact that a human being could see the other eight planets in the sky at the same time is incredible.
Therefore, the answer to the question of when the planets all align, is that they do not. At least, not in the way that the question is no doubt suggesting.
The planets do not all spin around the sun as if on a spinning plate in the circus; they are all orbiting in different ways and on different paths. For this reason, it is very unlikely that the planets will ever perfectly line up. But the term ‘planetary alignment’ used by scientists, simply means that the planets will be in the same region of sky at the same time.
This happens with two planets every now and again but will happen with all eight (excluding earth of course) in the year 2492.