Ratio of Orbital Distance to Transit Time

In summary: The ratio between the orbital periods and distances of the two fictional moons described by Swift in Gulliver's Travels is very close to the actual ratio observed in the moons of Mars discovered almost 150 years later. This shows that Swift was using known scientific principles and making educated guesses, rather than just pure imagination.
  • #1
Panda
197
0
I was reading Gullivers Travels to my son over Christmas and in a voyage to Laputa there is a passage illustrating their prowess at astronomy. The passage goes:

They have likewise discovered two lesser stars, or satellites, that revolve about Mars, whereof the innermost is distant from the centre of the primaryplanet exactly three of his diameters, and the outermost five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near the same proportion with the cubes of their distance from the centre of Mars, which evidently shows them to be governed by the same law of gravitation, that influences the other heavenly bodies.

Not being an expert in planetary physics I was wondering is this passage:

a) Correct, in which case what are the actual equations?
b) Incorrect, but was generally believed true in 1726 when the book was written?
c) Just a piece of fancy of "the Mad Parson" Jonathan Swift?
 
Astronomy news on Phys.org
  • #2
The equations are correct (Kepler's Laws). The answer to your question is (c). Deimos and Phobos were discovered in 1877.

From http://en.wikipedia.org/wiki/Phobos_(moon)#Jonathan_Swift.27s_.27prediction.27":
In part 3 chapter 3 (the "Voyage to Laputa") of Jonathan Swift's famous satire Gulliver's Travels, a fictional work written in 1726, the astronomers of Laputa are described as having discovered two satellites of Mars orbiting at distances of 3 and 5 Martian diameters, and periods of 10 and 21.5 hours, respectively. The actual orbital distances and periods of Phobos and Deimos are 1.4 and 3.5 Martian diameters, and 7.6 and 30.3 hours, respectively. This is regarded as a fascinating coincidence; no telescope in Swift's day would have been even remotely powerful enough to discover these satellites.​
 
Last edited by a moderator:
  • #3
Edit: Crossed post

It was just a "piece of fancy of "the Mad Parson" Jonathan Swift"; the satellites Phobos and Deimos not being discovered until 1877 by Hall in Washington DC.

However, remarkably, it was a very accurate "piece of fancy" as Phobos is 1.3 and Deimos 3.4 Mars diameters from the planet's centre. Phobos orbital period is 7.4 hours and Deimos 30.2 hours.

Garth
 
  • #4
Therefore Swift was using what Keplar had observed 100 years earlier, and just made up a few moons.

Is this ratio provable using laws of dynamics or similar or is it just by observation?
 
  • #5
Panda said:
Therefore Swift was using what Keplar had observed 100 years earlier, and just made up a few moons.

Is this ratio provable using laws of dynamics or similar or is it just by observation?

It is easily proven through Newton's laws of motion and Gravity.
 

1. What is the ratio of orbital distance to transit time?

The ratio of orbital distance to transit time is a measurement used in astronomy to determine the distance between a planet and its star. It is calculated by dividing the distance of the planet from its star by the time it takes for the planet to complete one orbit, also known as its transit time.

2. Why is the ratio of orbital distance to transit time important?

This ratio is important because it helps astronomers determine the size and mass of a planet, as well as its orbital period. By studying this ratio, scientists can also gain insight into the formation and evolution of planetary systems.

3. How is the ratio of orbital distance to transit time measured?

The ratio of orbital distance to transit time is measured using a technique called transit photometry. This involves observing a planet as it passes in front of its star, causing a small decrease in the star's brightness. By measuring the time it takes for this transit to occur, along with the size and brightness of the star, scientists can calculate the ratio of orbital distance to transit time.

4. What factors can affect the ratio of orbital distance to transit time?

The ratio of orbital distance to transit time can be affected by a variety of factors, including the size and mass of the planet, the mass and brightness of the star, and the presence of other planets in the system. Changes in any of these factors can alter the orbital distance and transit time of a planet.

5. How can the ratio of orbital distance to transit time be used to discover new planets?

The ratio of orbital distance to transit time is a key measurement used in the discovery of exoplanets, or planets outside of our solar system. By analyzing the transit data of a star and detecting any changes in its brightness, scientists can identify potential exoplanets and calculate their orbital distance to transit time ratio to confirm their existence.

Similar threads

Mathematica This Week's Finds in Mathematical Physics (Week 264)
    • MATLAB, Maple, Mathematica, LaTeX
Replies
6
Views
3K

Hot Threads

Recent Insights

Back
Top