What would happen if all the eight planets aligned?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

14 June 2020

After reading last week’s article about drawing a scale diagram of the solar system, Muthoni Nyaga and Cyrus Njeru separately asked me to comment on what would happen if all the planets to align on a straight line. Would their gravitational pull on the Earth cause significant effects?

Before considering what would happen, let us ask if this phenomenon is possible. Can the planets align into a straight line? There are a number of movies and fantasy books based on such an occurrence but the truth is that it cannot happen!

The reason is that the orbits of planets do not lie on the same plane. They are relatively close – within 7 degrees when viewed from the Sun – but not enough to allow for an alignment.

 The best we can get is a situation where they all fall in the same region of space with respect to the sun. This occurs because they travel in the same direction but at different speeds. Thus, they repeatedly overlap one another in their orbital journeys.

Take the case of Earth and Mars. They take 365 and 687 days, respectively, to go round the Sun. Since the Earth is faster, we can easily to see that it will overtake Mars after some days.

Picture the hands of a clock: suppose the center marks the location of the Sun, the tip of the hour-hand the position of the one planet and the tip of the minute-hand that of the other.

As the hands move round the clock, the faster minute hand overtakes the slower hour-hand several times. In a 12-hour period, this overtaking occurs 11 times. Now, there are 720 minutes in 12 hours; 720 divided by 11 is 65.45. Therefore, there is an overlap after every 65.54 minutes.

But, remember that the two hands are not on the same plane in the clock. The minute hand is normally mounted above the hour-hand. Thus, their tips (which mark positions of two planets) can never be on the same straight line with the centre of the clock.

By similar arguments, it turns out that the Earth overtakes Mars once every 779 days (approximately, 26 months). During this “overtaking” the two planets will be in the same region of space with respect to the Sun – the closest they can get to an alignment.

Furthermore, it is also easy to see that there are definite times when all the 8 planets fall in the same region of space when viewed from the sun. The last time this phenomenon happened was in the year 949AD and it is expected to occur again in 2492AD.

Having established that the planets cannot and will never align, it still remains interesting to investigate what could happen if they ever did. Muthoni and Cyrus were concerned about the effect of the gravitational attraction. This tells me that they know something about gravity – that it gets stronger as objects come closer.

So, how much extra gravity would we feel? See you next week.