Category Archives: Education

Retrograde Orbits

(note: This animation has no audio track.) – The Open University

Although many moons in the Solar System follow prograde orbits, there are some notable exceptions. The gas giant planets Jupiter, Saturn, Uranus and Neptune have several small outer moons that follow retrograde orbits; this means that they orbit their planet in the opposite direction to the planet’s rotation. In a retrograde orbit, a moon revolves in its orbit in the opposite direction from that in which the planet rotates about its axis.

Video by The Open University.

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A Brief History of the Universe

The universe is the biggest and oldest thing we know. It contains all existing matter and space. And its origin marks the beginning of time as far as we understand it. We don’t know what made the formation of the universe possible, nor why it occurred. The visible universe is currently about 93 billion light years wide.

A light-year is a distance that light travels in a year, which makes the universe about 880 trillion trillion metres wide. The visible universe is, however, still expanding, and we can measure that rate of expansion. Then, working backwards, we can figure out when the universe would have begun. To the best of our knowledge, the universe formed about 13.8 billion years ago in what is commonly referred to as the Big Bang.

This image shows the universe about 370000 years after the Big Bang, which is the oldest light that we’ve been able to record with the greatest precision. The image records ancient light or cosmic microwave background. The colours show tiny temperature fluctuations from an average temperature. These indicate areas of different densities, which became the stars and galaxies of today. Red spots are a bit hotter and blue spots a bit cooler. The image was recorded between 2009 and 2013, during the Planck mission, when the space observatory was operated by the European Space Agency, in conjunction with NASA, the National Aeronautics and Space Administration. Today, the universe is very cold. On average, it is 2.7Kelvin. Kelvin is a measure of temperature with the same magnitude as degrees Celsius. But 0 Kelvin equals minus 273.15 degrees Celsius.

In the universe, the hot parts, such as stars, make up only a tiny fraction. If we wind the clock backwards, the universe gets smaller. And this means the universe was hotter in the past. When matter gets hot, solids melt and liquids boil. The hot matter glows – red at first, but it becomes bluer as the temperature goes up. Eventually, all matter is gas. So we have a bright, glowing blob of gas. Going further back in time, as the gas gets hotter, the electrons are separated from the nuclei and a plasma is made. The temperature at this point is about 3000 to 6000 Kelvin and the glowing blob is white hot. As we go back further in time, the universe gets even smaller and hotter.

The nuclei themselves, containing protons and neutrons, are broken up. The reason for the breakup of nuclei is that the individual particles and the energy of the radiation are so great that the collisions of all this hot stuff are incredibly violent. The light is no longer in the visible spectrum. It is energetic enough to be x-rays and even gamma rays. Between just 10 seconds and 1000 seconds after the Big Bang, subatomic particles, including neutrons and protons, were formed. Neutrons live for just 9 minutes when they are free. Hence only those that stuck to protons during this period survived. All of the ordinary matter present today formed in this short window of time.

At about 1 microsecond after the Big Bang, the universe was very hot, at 10 to the 10 Kelvin, and quarks formed stable particles called hadrons. Before 1 picosecond, or 10 to the minus 12 seconds, the universe was an exotic place. The gas was hotter still and the laws of physics appeared different to how we see them today. The distinction between matter and radiation, such as light, cannot be detected. The forces of electromagnetism and the weak nuclear force also become indistinguishable. At the very earliest times, the universe was so hot and dense that we cannot yet describe them accurately.

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Insights on Teaching Japanese, in Japanese (and English) — Open Matters

By Joe Pickett, OCW Publication Director OCW has just published 21G.503 Japanese III, the third in a four-course sequence on Japanese taught at MIT. With relatively few Japanese speakers on the MIT campus, the instructors must make the most of what happens in the classroom and motivate students to work hard outside it. The course […]

via Insights on Teaching Japanese, in Japanese (and English) — Open Matters

Can a Theory be Proven Right?

This is based on one of the lectures of Richard Feynman (1918–1988), a theoretical physicist and Nobel Prize winner, describing the process by which theory and practical studies are used together to make scientific discoveries.

In general, we look for a new law by the following process:

First, we guess it. Then we compute the consequences of the guess to see what, if this is right, if this law that we guess is right, we see what it would imply. And then we compare those computation results to nature, or we say compare it to experiments or experience. Compare it directly with observations to see if it works. If it disagrees with experiment, it’s wrong.

In that simple statement is the key to science. It doesn’t make a difference how beautiful your guess is. It doesn’t make any difference how smart you are, who made the guess, or what his name is. If it disagrees with experiment, it’s wrong. That’s all there is to it. It’s true, however, that one has to check a little bit to make sure that it’s wrong, because someone who did the experiment may have reported it incorrectly. Or there may have been some feature in the experiment that wasn’t noticed, like some kind of dirt and so on. That’s an obvious check. Furthermore, the person who computed the consequences even may have been the same one who made the guesses, may have made some mistake in the analysis.

Those are obvious remarks. So when I say, if it disagrees with experiment, it’s wrong, I mean after the experiment has been checked, the calculations have been checked, the thing has been moved back and forth a few times to make sure that the consequences are logical consequences from the guess, and that it, in fact, it disagrees with a very carefully checked experiment. This will give you somewhat a wrong impression of science. It means that we keep on guessing possibilities and compare it to experiments. And this is to put an experiment on a really, a little bit weak position.

It turns out that the experimenters have a certain individual character. They like to do experiments, even if nobody’s guessed yet. So it’s very often true that experiments in a region in which people know this theorist doesn’t know anything, nobody’s guessed yet. For instance, we may have guessed all these laws, but we don’t know whether they really work at very high energy, because it’s just a good guess that they work at high energy. So experimenter says, let’s try higher energy. And therefore, experiment produces errors every once in a while, that is, it produces a discovery that one of the things that we thought of is wrong. So what I would say, if the experiment can produce unexpected results, and that starts to make us guess again. For instance, an unexpected result is a mu-meson and its neutrino, which was not guessed at by anybody, whatever, before it was discovered. And still, nobody has any method of guessing by which this is a natural thing.

Now you see, of course, that with this method, we can disprove any definite theory. You have a definite theory and a real guess from which you can really compute consequences, which could be compared to experiment, then in principle, we can get rid of any theory. We can always prove any definite theory wrong.

Notice, however, we never prove it right. Suppose that you invent a good guess, calculate the consequences, discover that every type of consequence that you calculate agrees with experiment. Is the theory then right? No. It is simply not proved wrong. Because in the future, there could be a wider range of experiments that compute a wider range of consequences, and you may discover that the thing is wrong. That’s why laws like Newton’s laws for the motion of planets last such a long time. He guessed the law of gravitation, calculated all the kinds of consequences for the solar system, and so on, compared them to experiments, and it took several hundred years before the slight error of the motion of Mercury was developed.

During all that time, the theory had been failed to be proved wrong and could be taken to be temporarily right. But it can never be proved right, because tomorrow’s experiment may succeed in proving what you thought was right, wrong. So we never are right. We can only be sure we’re wrong. However, it’s rather remarkable that we can last so long. I mean, Have some idea which will last so long.


Google and Udacity partner for Android New Nanodegree course

Google and Udacity are teaming up again, this time for an Android Basics course that will earn you a Nanodegree.
The two companies have partnered before for Android Nanodegree programs, but this one is meant for those who are starting from absolute scratch: no coding experience required.
Like the other Android Nanodegree programs, students learn directly from Google staffers. It offers the same mentorship and code review as any other Nanodegree program, too.
the program teaches the basics of Java, as well as how to interact with Web APIs. Students also learn how to interact with a SQLite database.
The first 50 students who graduate the course will earn a scholarship toward the rest of the Android Nanodegree career track. If you’re interested, Udacity is accepting enrollments starting today.

Free Astronomy Books

Free Astronomy Books – Primarily for education.

Feel free to add your own links to free books. Let me know if there are broken links or copyright issues.

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