So, about Tycho Brahe...

Hello followers. You guys have heard me mention Tycho Brahe at one point or another, and in my last post I said that I would touch upon our relationship. Well, here we go.

Tycho was an astronomer who spent years carefully measuring the positions of the stars and planets to an unprecedented accuracy. He was not particularly gifted in mathematics, however, and could not make sense of his observations. That's where I came in. I don't usually brag, but I must say that I am an incredibly gifted mathematician, and Tycho recognized this. He offered me a position as an assistant so I could make sense of his observations, and offered to mentor me.

There were a few problems with our relationship, though. We did not get along at all, due to our varying opinions on the universe. As stated before, I strongly believed in Copernicus's heliocentric model of the universe. Tycho, on the other hand, developed his own model where the Sun and the moon circled the Earth, and the other planets circled the sun. Also, my lifestyle differed very much from his. He was born into an upper class lifestyle, and enjoyed throwing lavish feasts and often gorged himself with food and wine.

Another reason for our quarreling was due to the fact that Tycho did not trust me. He saw me as a potential rival, and feared that I would use his research to become more famous than him. He also wasn't eager to have his work used to support the Copernican theory as opposed to his own. So he withheld his information from me, and kept me busy with the task of studying the orbit of Mars. I spent eight years working on the orbit of Mars, and as it turned out it was a good basis to research many of my theories.
Tycho's lifestyle caught up with him, though, and he became very ill after a banquet and soon died. Tycho's heirs were eager to make money off of his information, and I had to take...ahem, drastic measures to achieve the information that led me to formulate the Laws of Planetary Motion. I admit it, I stole his information. But just think about what I was able to accomplish! It was all for a good cause, right? I'm sure modern physicians are glad I did it.

All's well that ends well, right? Although I did not agree with Tycho on many levels, he was a brilliant observer and without him I could not have accomplished much of my work. Until next time,

Johannes Kepler

"Billions and billions of stars..."

In my next post, I hope to talk a bit about my mentor Tycho Brahe. He is...interesting, to say the least. But it's been a long day, so as an introduction I'll share a video with Carl Sagan.

Pretty accurate, I must say. It also talks a bit more about ellipses, which I have already covered. Still, you can never learn too much about ellipses!
Until next time,
Johannes Kepler

Last but not least...

Hello readers. I have already written blog entires about the first two laws of planetary motion, and now the wait is over. I will be sharing with you, today, the third and final law of planetary motion. Let's not hold the suspense any further and dive right into it, shall we?

The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

There you have it, the third law. I know what you must be thinking: What? Actually, it's not that complicated. Especially after that long explanation about ellipses, I'm sure you guys can handle anything. What is fascinating about this law is that it doesn't just apply to the planets in our solar system, but also their moons, dwarf planets and asteroids, satellites going round the Earth, and more. It doesn't work, however, when the mass of the secondary body is a significant fraction of the primary body. If this is the case, then the law has to be tweaked a bit. But for most things in our solar system, like the planets orbiting the sun, this 100% works.

What the third law says is that the amount of time that a planet takes to revolve around the sun is directly related to the semi-major axis. Forget what the semi-major axis is? It's the distance of a planet from the Sun as it orbits. Therefore, the amount of time that a planet takes to make a full orbit is directly proportional to how far it is from the sun. For example, it takes Mercury, the closet planet to the sun, about 88 days to make one full orbit, while it takes Earth, the third closest planet to the sun, 365 days.

And that, my friends, concludes my three laws of planetary motion. I hope you enjoyed my explanations, and look into it even furthur!

Johannes Kepler Song?

This certainly got a chuckle out of me. The lyrics include astronomers such as Galileo and Copernicus, plus the tune is rather catchy, I must admit.


Check it out!

Second is the best

Ok, so second isn't necessary the best. Coming up with clever titles is difficult, alright? I'm an astronomer, not a poet. The point is, today I am going to provide you with an explanation of the second law of planetary motion. Excited? You should be. Let's get started.
The second law of planetary motion is called the Law of Equal Motion. I shall begin by stating the law.
An imaginary line joining a planet and the sun sweeps out an equal area of space in equal amounts of time.

Above, you can see how the planet moves around the sun. Notice how when the planet is closet to the sun, it moves more quickly than when it is farther away. Nevertheless, the area of each sweep and the time of each interval is the same no matter where the planet is on its orbit.


Well, that was quick, wasn't it? I might even have time to catch that special about White Dwarfs on the Discovery Channel! Until next time,
Johannes Kepler

Shameless Promotion

Hello trusty followers. I don't know if you're aware, but there is a fascinating website called Amazon that allows you to order books right from your computer at home.


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They have 5 of my books available for purchase, so please, click on the link above and order them. I'm in desperate need of a new telescope.

I'm considering the above model, a CPC 1100 GPS. If you click on the picture, it will bring you to the Celestron website. It's a bit steep in terms of price, but just look at the sleek design!

A funny thing called an ellipse...

An explanation of the first law of planetary motion.

As you can probably recall, my previous entry was a brief intoduction to the Laws of Planetary Motion, three laws that I made known to the world after years of laborious work. That aside, I intend to go more in depth about each law, beginning with the first one: the law of ellipses.


I have always been a supporter of the Copernican Theory. That is, I believe in the heliocentric model of the universe; heliocentric meaning that the planets, including the Earth, revolve around the Sun. I strongly disagree with the once widely accepted model that Ptomely developed, which cemented the geocentric theory for several centuries. Geocentric means that the universe revolves around the Earth, as opposed to the Sun. Copernicus's theory, however, was no better at predicting the positions of the planets in the sky than the Ptolemy. I knew that something had to be missing, and so my research began.
Using Tycho Brahe's observations of Mars (you will be hearing much more about Tycho, I can assure you), I noticed that the orbit of Mars did not fit Copernicus's model, in which the planets orbited in perfect circles. I did not want to believe that my discoveries were true at first, because they would contradict the ideas put forward by both Copernicus and Aristotle. However, finally I was forced to realize the truth. While Copernicus was correct in placing the sun in the center of the universe, the planets did not orbit in a circular motion.
They orbited in an elliptical motion.

This picture is fairly clear in demonstrating the elliptical movement of the planets. Notice how the shape is like a flattened circle, this is the elliptical orbit.

Now, the properties of an ellipse are very complicated, and I will try to keep this as simple as possible. There are two points for an ellipse called foci (singular: focus), and the sum of the distances to the foci from any point on the ellipse is a constant. You might be asking yourself, how does this relate to the position of the Sun? Well, the Sun is at one focus of the ellipse.

See? It's really pretty straight-forward. The distance between the planet and the Sun is constantly changing as the planet orbits around the Sun.

We're not done quite yet, so hold tight. I'd like to introduce an important term, the term being eccentricity. As you can see below, as eccentricity increases, the ellipse appears to flatten. So, if the eccentricity of an ellipse was equal to 0, then it would be a circle. This is what threw many people off, including Copernicus; The orbit of most planets have such a small eccentricity that they cannot be determined by first glance. Careful measurements must be taken in order to prove that the orbits are, in fact, elliptical.

Lastly, an ellipse has two axes called the minor axis and the major axis. Half of the major axis is called the semimajor axis, which is equal to the distance of a planet from the Sun as it orbits.

There you have it, a fairly simple explanation about ellipses. Keep a look out for my next blog, which will be about my second law of planetary motion.