Planetarium

"Venus and Jupiter are going to be very close together on July 1st, you wrote in a recent article. Will these two planets being so close together affect Earth gravitationally? Will we have higher tides or anything like that?"

 

- Pierre Auguste Renoir

(Please let me be anonymous or make up a name for me.)
           
Well, Pierre, that article obviously made an impression on you. Ha ha ha!

On the surface, this query would seem like a yes or no question, and it certainly could be one were we to decide to be lazy tonight. However, we'll sweat out the details.

Yes, Venus and Jupiter will affect us gravitationally, as they always do. The effect won't be noticeable and will not increase the tides. This matter relates directly to Newton's Law of Universal Gravitation which states that "Every massive object gravitationally attracts every other massive object. The magnitude of the gravitational attraction is proportional to the masses of the bodies and inversely proportional to the squares of their separation distance."

An object's mass determines its gravitational influence: the more massive it is, the greater its pull. This "pull" is reduced, however, if the object moves away. If the object's distance is doubled, the gravitational attraction is diminished to one quarter of its original value. Triple the distance, and attraction is just one-ninth as powerful.*

On July 1, Venus and Jupiter will appear to be nearly aligned. This close alignment is illusory, as Venus will be about 49.8 million miles from Earth on July 1st. Jupiter will be 565 million miles from Earth. With more than 500 million miles of space between them, the planets will hardly be hobnobbing. One might wonder, though, if having them both "together" along our sight line will pose any dangers to the planet.

So, we adjourned to the crystalline sphere room and crunched the numbers. (Or, to be a little more honest, we had that frothing Tasmanian devil Uber Professor Trinket crunch the numbers.) Noting that Venus is only eighty one percent as massive as Earth and Jupiter is 317 times as massive as Earth, Trinket determined that the the combined gravitational force exerted by Venus and Jupiter amounts to less than two percent of that induced by the moon.   

The differential gravitational force, which relates to the difference between the gravitational force exerted onto the point on Earth nearest and farthest away from the two planets, is even less. The farther away a body is from Earth, the less powerful will its differential forces tend to be. (The contribution the planets make to the tides amounts to less than half an inch.)

Venus and Jupiter, along with the Sun, moon, the Pleiades Star Cluster, the Andromeda Galaxy, and your Aunt Bertha, all exert a gravitational force on you by virtue of their masses. Of course, the Sun and moon affect us most profoundly by virtue of their proximity. Even though Venus and Jupiter will appear to gather together, we'll feel nothing at all.
   

*A brief math moment: to square a number is to multiply it by itself. 2 x 2 = 4. The inverse square means that the squared number is in the denominator, so if you double the distance, the gravitational attraction is reduced to 1/4 of its original magnitude.