APOD: Retrograde Mars and Saturn (2016 Sep 15)

[APOD Robot]

Retrograde Mars and Saturn

Explanation: Wandering Mars and Saturn have spent much of this year remarkably close in planet Earth's night sky. In a sequence of exposures spanning mid-December 2015 through the beginning of this week, this composited skyview follows their time together, including both near opposition, just north of bright star Antares near the Milky Way's central bulge. In the corresponding video, Saturn's apparent movement is seen to be back and forth along the flattened, compact loop, while Mars traces the wider, reversing S-shaped track from upper right to lower left through the frame. To connect the dots and dates just slide your cursor over the picture (or follow this link). It looks that way, but Mars and Saturn don't actually reverse direction along their orbits. Instead, their apparent backwards or retrograde motion with respect to the background stars is a reflection of the orbital motion of the Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit.

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[Boomer12k]

Ah, yes, Students....Epicycles is the answer....What????? Ptolemy was wrong???

Even "great" scientists can be wrong....even using "science"...

Well... I have been wrong myself....so I am in good company.

I have been out testing my Meade 6" EXT-LS... looking at Mars and Saturn... unfortunately it is having some troubles, and will probably be replaced. "Locating" and Alignment issues... But the view is great. The Moon is awesome, even with a 40mm eyepiece, to see the whole nearly full Moon tonight was great.

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[Markus Schwarz]

Even "great" scientists can be wrong....even using "science"...

If you want to have good ideas you must have many ideas. Most of them will be wrong, and what you have to learn is which ones to throw away.

[BillT]

It's interesting that Aristarchus and other Greeks of the time had proposed the heliocentric view. Even the Roman's Pliny and Seneca wrote that the retrograde motion of the planets was merely "apparent". That suggests that the heliocentric model was more widely accepted than is often stated. We know the view of Aristotle and Ptolemy won out in the end until Copernicus began setting things straight. What a shame Aristarchus book promoting Heliocentrism is lost and we don't know what arguments he used.

[Boomer12k]

Even "great" scientists can be wrong....even using "science"...

If you want to have good ideas you must have many ideas. Most of them will be wrong, and what you have to learn is which ones to throw away.

Problem is... most are too focused on their Theory, and think they are correct... I call it Fred Hoyle Syndrome... Don't make theories... and unfortunately sometimes all the good ideas are taken....LOL.

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[Boomer12k]

It's interesting that Aristarchus and other Greeks of the time had proposed the heliocentric view. Even the Roman's Pliny and Seneca wrote that the retrograde motion of the planets was merely "apparent". That suggests that the heliocentric model was more widely accepted than is often stated. We know the view of Aristotle and Ptolemy won out in the end until Copernicus began setting things straight. What a shame Aristarchus book promoting Heliocentrism is lost and we don't know what arguments he used.

It IS a shame... we could have had a more accurate view of the Solar System a lot earlier, it would have helped advance things... it is too bad the "authoritative" opinion and "proof" often wins out, because of fame, even in Court... Also if the church had not persecuted and threatened when their view was challenged...and they felt their authority was threatened... We would have had it again, earlier, in the time of Galileo....

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[rstevenson]

... Problem is... most are too focused on their Theory, and think they are correct... I call it Fred Hoyle Syndrome... Don't make theories... and unfortunately sometimes all the good ideas are taken....LOL.

Wrong word. Theories in science are well established, supported by multiple lines of enquiry, and are as close to fact as you can get in science. You are talking about hypotheses, which are closer to guesses, and are usually starting points for further exploration, if they don't get ignored because nothing is found to support them.

As for Fred Hoyle, he just wandered out of his specialty a few too many times. Can happen to anyone, scientist or not.

Rob

[Ann]

It's interesting that Aristarchus and other Greeks of the time had proposed the heliocentric view. Even the Roman's Pliny and Seneca wrote that the retrograde motion of the planets was merely "apparent". That suggests that the heliocentric model was more widely accepted than is often stated. We know the view of Aristotle and Ptolemy won out in the end until Copernicus began setting things straight. What a shame Aristarchus book promoting Heliocentrism is lost and we don't know what arguments he used.

Indeed. And think of Democritus, who postulated the atom.

The problem for the Greeks was that they had few means to test their hypotheses. And since they couldn't back up their hypotheses with (much) observational evidence, and since the most influential thinkers of their day believed in a geocentric universe created and ruled by gods, the world views of these pioneers were forgotten for many centuries.

Ann

[Markus Schwarz]

The problem for the Greeks was that they had few means to test their hypotheses. And since they couldn't back up their hypotheses with (much) observational evidence, and since the most influential thinkers of their day believed in a geocentric universe created and ruled by gods, the world views of these pioneers were forgotten for many centuries.

I am no historian, but from what I have read the observational evidence at the time of the ancient Greeks did favour a geocentric model (see second paragraph of the Wikipedia article).

Also, the modern view is that the debate, whether geocentrism or heliocentrism is correct, is now obsolete. Both coordinate systems can be used to describe the motion of the planets; it just so happens that the coordinate system where the Sun is at the center allows for a relatively easy description of planetary motion. My colleagues were to surprised to learn that but this is indeed what general relativity tells us (see here).

[Ann]

The problem for the Greeks was that they had few means to test their hypotheses. And since they couldn't back up their hypotheses with (much) observational evidence, and since the most influential thinkers of their day believed in a geocentric universe created and ruled by gods, the world views of these pioneers were forgotten for many centuries.

I am no historian, but from what I have read the observational evidence at the time of the ancient Greeks did favour a geocentric model (see second paragraph of the Wikipedia article).

Also, the modern view is that the debate, whether geocentrism or heliocentrism is correct, is now obsolete. Both coordinate systems can be used to describe the motion of the planets; it just so happens that the coordinate system where the Sun is at the center allows for a relatively easy description of planetary motion. My colleagues were to surprised to learn that but this is indeed what general relativity tells us (see here).

Certainly neither the geocentric or the heliocentric model is correct. The Sun is not at the exact center of the solar system, and the solar system is definitely not at the center of the universe! (The center of the universe, coincidentally - as Chris has pointed out - is more likely the exact moment of the Big Bang, since everything has been flowing out of that.)

But I think it can definitely be argued that as far as the solar system is concerned, the heliocentric model is a far better description of it than the geocentric one. Certainly that is true if we consider the motion of all the planets in the solar system. (I'm not saying that a geocentric world view can't be mathematically constructed, but doing such a thing seems pointless to me. After all, we know that planets are born out of the protoplanetary disks that surround newborn stars - so how reasonable is it to say that the star is orbiting the disk, rather than the other way round?)

So the reason why Aristarchos and the others didn't win out is that they didn't have enough political clout. Those who preferred the heliocentric universe, made and ruled by gods, were simply stronger and therefore had their way.

Why did the heliocentric model win in Renaissance Europe? I'm just speculating, obviously, but I think it has to do with the fact that Isaac Newton first and foremost was a mathematician, and early 17th century England - poised on the threshold of ever greater power, and eventually on world domination - probably realized the value of a superb mathematician, whose mathematical formulas could solve so many mechanical and engineering problems for them, thus making them ever more invincible.

The heliocentric model had already gained credibility, thanks to Johannes Kepler (and Tycho Brahe). Using Brahe's superb observations of the solar system, Kepler was able to mathematically prove that the planets follow elliptical orbits. The world likely didn't change much right away due to Kepler's breakthrough, but Newton could apply his celestial mechanics to show why planets follow elliptical paths. Besides, Newton's cosmology was also acceptable from a religious point of view. Rather than dethroning God, Newton turned the deity into the omnipotent clockmaker of the universe. In England, those in power probably liked the idea of a god that had given them a lot of leeway by constructing the clock-universe and winding it up, but had then opted to stay in the background to allow enterprising and clever people (like themselves) to explore and conquer their world.

Moral: You don't necessarily win because you are right, but because powerful people like your ideas.

Ann

[Chris Peterson]

Certainly neither the geocentric or the heliocentric model is correct. The Sun is not at the exact center of the solar system, and the solar system is definitely not at the center of the universe! (The center of the universe, coincidentally - as Chris has pointed out - is more likely the exact moment of the Big Bang, since everything has been flowing out of that.)

Whether or not the Sun is the center of the Solar System isn't a question of science, but rather, a question of how we define the center of the Solar System. If we define it by the center of the Sun, so it is. If we define it by the center of gravity of everything in orbit around the Sun, it isn't.

BTW, I've also noted that from a strictly spatial consideration, the Universe has no unique center, but that in essence any point can be treated as central (since the Universe extends the same distance in all directions from any point). So we could quite reasonably say that the Solar System is the center of the Universe. It's just not a particularly privileged center.