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Mercury -- Not Venus -- is the Closest Planet To Earth on Average, New Research Finds (gizmodo.com)
That's the finding presented by a team of scientists who have published their results this week in an article in the magazine Physics Today. From a report: They explain that our methods of calculating which planet is "the closest" oversimplifies the matter. But that's not all. "Further, Mercury is the closest neighbor, on average, to each of the other seven planets in the solar system," they write. Wait -- what?
Our misconceptions about how close the planets are to one another comes from the way we usually estimate the distances to other planets. Normally, we calculate the average distance from the planet to the Sun. The Earth's average distance is 1 astronomical unit (AU), while Venus' is around 0.72 AU. If you subtract one from the other, you calculate the average distance from Earth to Venus as 0.28 AU, the smallest distance for any pair of planets. But a trio of researchers realized that this isn't an accurate way to calculate the distances to planets. After all, Earth spends just as much time on the opposite side of its orbit from Venus, placing it 1.72 AU away.
One must instead average the distance between every point along one planet's orbit and every point along the other planet's orbit. The researchers ran a simulation based on two assumptions: that the planets' orbits were approximately circular, and that their orbits weren't at an angle relative to one another.
Our misconceptions about how close the planets are to one another comes from the way we usually estimate the distances to other planets. Normally, we calculate the average distance from the planet to the Sun. The Earth's average distance is 1 astronomical unit (AU), while Venus' is around 0.72 AU. If you subtract one from the other, you calculate the average distance from Earth to Venus as 0.28 AU, the smallest distance for any pair of planets. But a trio of researchers realized that this isn't an accurate way to calculate the distances to planets. After all, Earth spends just as much time on the opposite side of its orbit from Venus, placing it 1.72 AU away.
One must instead average the distance between every point along one planet's orbit and every point along the other planet's orbit. The researchers ran a simulation based on two assumptions: that the planets' orbits were approximately circular, and that their orbits weren't at an angle relative to one another.
https://physicstoday.scitation...
Interesting work with the best message to get out of this; don't rely on what's obvious, test what you think is true.
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Amatuer astronomers love to observe Mars. The problem is Mars is on a close, but outside orbit. Unlike Jupiter and Saturn, which the Earth passes every year in thier orbits, it is a different story with Mars. It is only really close for two months every 2 years. It spends most of its time on the far side of its orbit until the Earth can chase it down again, and then quickly races away. Even though you can view it through most of its orbit, it is small and normally far away. Venus, even when near the far side of its orbit, it is fairly easy to observe. At least once it rises far enough out of the Sun's glare. Mercury would be even better, but due to the small orbit it doesn't get far from the Sun from our point of view before it dives back down into the glare.
Well, shit, I need to recalculate my horoscope again.
I saw some comments on the Physics Today article about this being pedantic, but astronomy is and always has been about pedantry. It's taking into account tiny details and vanishingly small deviations that allows us to do things like observe the composition of faraway stars or compute the age of the universe.
If perfectly circular, average distance from any planet to any planet should be equal to the center of their path circle, which is, drum roll please, the center of the sun.
No? Planet A at 1AU orbit and Planet B at 2AU orbit have distance between 1AU and 3AU. Planet C at 1000AU has distance to planet A between 999AU and 1001AU. Whatever are their periods, some average of 1-3 won't get anywhere close to average of 999-1001.
So, Earth-Mercury average distance shares the first place with any other of 45 planet pair combinations.
Not sure how you came up with number 45. 8 planets give 28 combinations, so it should be 'any other of 27 combinations'. Even if you didn't get memo from 2006 about Pluto, it would be 36-1=35 combinations.
Seriously, there are more important problems to solve. How about something that's actually useful?
Hey, now, this research evelated pedantry to a whole new level! If ever there was a story that belonged on Slashdot...
But I don't get why they "simulated" this. Isn't this just an integral?
Socialism: a lie told by totalitarians and believed by fools.
No. Distance is a scalar, not a vector. So the average distance doesn't work out to the center of the sun. It works out to the the sum of all points along the circular orbit. For Venus' case, since its orbit is bigger, the scalar distance to each equivalent point in Mercury's orbit is on average bigger because it's at a greater angle from the Earth (with Earth-to-sun line being the shortest distance).
e.g. Pretend Mercury is located in the sun, and Venus has the same orbit as Earth. Consider four points on each orbit spaced 90 degrees apart.
Average these four points. The first two cancel out (both average a distance R). The second two result in Mercury being at distance R, Venus at 1.414R. And hence Mercury is on average closer than Venus, even though we're pretending Venus has the same orbit as the Earth.
The best kind of Correct.
You're obviously not married.
It must have been something you assimilated. . . .
Actually, they did pure math with those simplifying assumptions first. Then they ran a simulation using the actual orbital characteristics (PyEphem uses the real orbits) to check.
That simulation then demonstrated that the assumptions in the pure math produced an error of under 1% for relations among the major planets.