Daily Science Dump: Kepler’s First Law Edition

Daily Science Dump: Kepler’s First Law Edition

Bonjour my science nerds. I got a question regarding Kepler’s Three Laws because they can be somewhat confusing. And tbh, they really are. Because they can be a bit of a pain, I’ve decided to break this up into 3 sections, one for each law. They generally follow the same idea: planetary orbits are not circular. The difference between each law resides in the minute details. And because they are really detailed, I wanted to make sure I covered everything of each law so they don’t get confused. Let’s get started!

Kepler’s First Law of Planetary Motion

History

Before we get into the actual laws, we need to understand why these laws are so important. During the 1500s and early 1600s, astronomy was starting to become a big deal. We were trying to figure out where we are in the universe. During this time period, the famous geocentric and heliocentric models were stirring up massive controversy in the Catholic Church (for obvious reasons). Ptolemy brought around the geocentric model, which put Earth at the center. This was a natural thought at the time because it was a religious concept that man was God’s greatest creation, so God would want to put man at the center of everything (little presumptuous on our part tbh). Next, Copernicus said that our Sun was in the center, and all the planets orbit around the sun. This clearly didn’t go down well with the Church because it was the first instance of defying the Catholic Church, therefore defying God. In an attempt to settle down the controversy, Brahe brought around a new theory model, putting the Earth at the center, having the Sun and Moon orbiting the Earth, and then the rest of the planets orbiting the Sun. It was a very far reached model but people bought it. All of these models had one thing in common; all the orbits of the planets were circular. But none of none of the actual data fit with perfect circular orbits. This is where our boi Kepler comes in. 

It was long believed that the planets should orbit along circular paths, because a circle is considered an ideal shape. But as I mentioned before, none of the data was fitting the circular shape, particularly Mars. Kepler brought around another shape, the ellipse, to explain the missing pieces of the data. An ellipse is like a flattened circle with some important properties that Kepler used for his laws. His first law focuses more on explaining the patterns of elliptical orbits. The second and third law goes into more detail on the properties of elliptical orbits. 

If you’ve taken a simple geometry class, you know the basic principles of ellipses. We know there’s a major-axis and minor-axis (the diameter horizontally and the diameter vertically), the focal points, and eccentricity. All of these are important for planetary orbits. If we take a trip back to geometry, we know that the positions of the focal points affect the eccentricity, which is basically how much it’s being squished (if e = 0 then it’s a perfect circle and if e = 1 it’s a parabola). 

All of this geometry going on transfers over into planetary motion. In this case, the Sun acts as one of the focal points. The other focal point is merely imaginary. Mathematically it exists but there’s nothing at that point in space that says “Hey! I’m a focal point for Saturn!”. But we know for sure that the Sun is on of the two focal points. This revelation caused a lot of uproar and many refused to believe it. Partly because the orbit of a lot planets are so close to a perfect circle it’s extremely hard to tell it’s elliptical at all. 

Eccentricity has to stay between 0 and 1, like I explained earlier. An eccentricity of 0 is a perfect circle. If it’s 1 or greater, it’s a parabola. For the planetary motion, most of the planets’ eccentricity doesn’t even crack 0.1 (Pluto has a bit over 0.2 but apparently Pluto isn’t a planet #JusticeForPluto). Earth’s eccentricity is currently 0.0167, which means its very very close to a perfect circle. But not quite. To be quite honest, the fact that Kepler was able to figure out that the orbits were not circular is astonishing.

So that’s it for Kepler’s First Law of Planetary Motion! These laws were critical in understanding how our universe works and how our solar system plays out. It opened our eyes to many new ideas and thought processes. This law is just the first step of understanding the orbital tendencies of planets. On Friday, we will dive right into Kepler’s Second Law of Planetary Motion which goes into detail about the speed of the planet due to the elliptical orbit.

Don’t forget, I’m updating the Blog Website everyday with something new because I have no life…. I added cool space music! If you have any cool song recommendations for the playlist definitely shoot me a message!

If you have any questions about today’s Daily Science Dump or any past ones, don’t be afraid to ask!

As always,

Stay Nerdy!

R.L.