Tuesday, January 1, 2013

Johannes Kepler

If Tycho Brahe was great at raising money, and making careful observation, but not so great with theory, Johannes Kepler, who worked with Brahe in the second observatory that brahe built, near Prague, was great both at observation and at theory.
After having analyzed the orbit of Mars, following a suggestion from Tycho Brahe, Kepler realized started forming the first tow of his three rules of planetary motion in the early 1600s.
The third law of motion had to wait until the late 1610s.
Kepler was a part of the Catholic Lutheran wars of his period, and his mother was tried as a witch,
It took a while for his theories to be accepted, but today they are an important part of astronomy.

Kepler's laws are:
1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.[1]
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. 

Tuesday, December 25, 2012

Tycho Brahe

First, let me apologize for the delay in writing this blog post. Sometimes my time is taken by other things. I hope that as the saying goes, heaven can wait...

Tycho Brahe (1546-1601) was a Danish astronomer, and alchemist.
As I said in the previous post, in Copernicus' time there was no compelling reason to believe the Copernican theory. If the orbits of the planets are circular, the preference for the location of the center of the circle is mainly aesthetic.
However, Tycho Brahe's observations contributed to the theory (formed by Kepler, more about him in the next post) that the orbits of the the planets around the sun are not circular but Elliptical.
Brahe first built an observatory in his native Denmark  but after some disagreement with the danish king he moved to Prague, and built an observatory there.
Though Brahe had his own theories about the orbits, these were discredited soon after his death. However, the accuracy of his measurements, and their sheer quantity, contributed to our later understanding of the orbits as elliptical.

Tuesday, November 27, 2012

The Revolution Goes On

Usually when speaking about the Copernican revolution, or indeed any other revolution, whether in science or in other fields of human endeavor, people tend to assume, and describe the revolution as a 'one off' thing.
'So we thought the Sun revolved around the Earth, and then along came Copernicus, and now we know the Truth'.
Doubtless this kind of description simplifies life, but it also oversimplifies life.
When Copernicus was done with his revolution, the model describing the solar system was simpler, but not much better. i.e., it did not yield better predictions about the movement of the planets.
The ultimate description of the solar system (before Einstein's General Theory of Relativity) had to wait for Newton, and his universal law of Gravitation.
But Newton or Kepler could not form their better models without the observations of Tycho Brahe.
More about Tycho Brahe in next week's post, until then, enjoy his portrait above.

Monday, November 19, 2012

Copernicus Was Afraid of the Copernican Revolution

Nikolai Copernicus lived in what is now Poland in the years 1473-1543. That means he lived to be a bit more than seventy, which was a very respectable age at the time. 
BTW, Krakow, where Copernicus studied, was also a part of Poland when Copernicus was alive, and furthermore at the time Poland had enjoyed a golden age. However, some time after Copernicus' death Poland and Lithuania became a commonwealth, and then later it gets even messier, but during the 20th century Poland once more became an independent nation, so everything is fine that way.
After finishing his studies in Krakow, Copernicus went to work for his uncle who was the independent prince in a place called Warmia (close to Krakow and Prussia). He wrote early drafts of his groundbreaking theories already in 1514, but he did not publish his work till several months before his death in 1543.
Turns out that by 1532 the work was mostly done, but Copernicus did not want to publish it because he did not want to risk the scorn "to which he would expose himself on account of the novelty and incomprehensibility of his theses." (This quote is from the Wikipedia article about Copernicus, that I highly recommend).
In 1533, Johann Albrecht Widmannstetter delivered a series of lectures in Rome outlining Copernicus' theory. Pope Clement VII and several Catholic cardinals heard the lectures and were interested in the theory.
Despite urgings from many quarters, Copernicus delayed publication of his book, perhaps from fear of criticism—a fear delicately expressed in the subsequent dedication of his masterpiece to Pope Paul III. Scholars disagree on whether Copernicus' concern was limited to possible astronomical and philosophical objections, or whether he was also concerned about religious objections.
However, despite his timidity, here is how the Wikipedia presents Copernicus:
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe.
Copernicus' epochal book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published just before his death in 1543, is often regarded as the starting point of modern astronomy and the defining epiphany that began the scientific revolution.
I tend to agree.

Saturday, November 10, 2012

The Trouble with Geocentrism

Suppose we teach science to kids in high school ,and we want them to consider two competing theories:

  • According to the first theory the sun is in the middle of the universe
  • According to the second theory the earth is in the middle of the universe.
Of course both theories are wrong, but supposedly disproving the first one would be harder for high school students, unless they have very sophisticated equipment...
So how would these high school students disprove the second theory?
Turns out it's not that easy to disprove either!
Galileo managed to observe the phases of Venus which is a nice counterexample, because it's not supposed to have all phases according to the way the Ptolemy placed it in his model. However, the Geocentric model can survive this criticism if it's changed a bit...
The infamous epicycles of the Ptolemaic model are supposed to be less elegant than the simple circles in the Copernican model. However, the simple circles in the Copernican model are not more accurate than the Ptolemaic model, because the real course of the planets is elliptical and not circular.
So the Copernican model is far from perfect, and it would take centuries before the argument is settled, but nevertheless it represents a huge revolution.
More about this next week.

Tuesday, October 30, 2012

A Personal Copernican Revolution

In the next few weeks I would like to discuss the 'real' Copernican Revolution: why it happened, what happened before it, it repercussions, and whether the Scientific Revolution ended or whether it is still going on.
But before that, I would like to apologize or at least explain:
I have started this blog several months ago, posted in it some general comments about what it is going to be like, and then suddenly stopped.
The reason for this is that I pretty much had to change my whole life around in the past few months.
Suffice it to say that I had a pretty steady income writing curricula for the US education system, and now I more or less work as a teacher in Israel, and studying to get my Israeli teaching licence.
On the one hand that makes me very busy.
On the other hand I do much less writing on a regular basis, so that should leave some more 'writing time' for this blog...
I think I'll be able to post more regularly here, at least in the coming few months.

Tuesday, September 11, 2012

The Almagest is an Impressive Bit of Science

Usually when people tell the story of modern Physics, they start with Copernicus, and I promise I'll get to the guy. probably by next week.
But this blog does not wish to tell story in which the 'dark middle ages' were suddenly illuminated by the bright light of gravity, and then Enlightenment.
Rather, this blog is trying to tell a story of gradual development. Of people working really hard, sometimes centuries apart, in order to gain a better understanding of the universe.
In the first two centuries CE, Egyptian, Greek and Roman astronomers were working as hard as they could to understand and map the heavenly bodies. These efforts culminated with the Almagest.
A 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt, it is one of the most influential scientific texts of all time, with its geocentric model accepted for more than twelve hundred years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus.
While today we don't use the Almagest, it is important to remember that as a predictive model of, for example, solar and lunar eclipses, it is pretty good. 
The Almagest represented science at its best for a very long period of time, but like almost all science, it got old after a while, and newer, simpler models were rushing to fill its place.
More about that next week.