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Kepler’s Laws (KL) are super fundamental. They tell us how planets orbit. These laws also work for comets, moons, and pretty much everything.
When Does KL Apply?
KL works best when the object’s mass (its “stuff”) is negligible. This is true for pretty much anything in our universe.
How KL Was Found
Johannes Kepler (JK) discovered KL using super-accurate notes (observations). The first two KL came out in 1609, his volume.
Before JK, Copernicus thought planets moved in perfect circles (imagine a perfect circle). JK showed they actually move in ovals (called Elliptical Orbits (EO)), specifically. Later, Isaac Newton (IN) found the Law of Gravity (LoG) in 1687.
The Three Laws of Kepler
1. Kepler’s First Law (K1L): The Path is an Oval!
Planets move in an elliptical path (EP) constantly. The sun isn’t right in the middle; it’s at one special focus. This means the Sun constantly pulls the planet inward.
- Think of it like this: If you swing a ball on a string, your hand is the Sun, and the string is the bond.
2. Kepler’s Second Law (K2L): Equal Areas, Equal Times!
Imagine a line from the Sun radially. This line sweeps out equal areas. This means a planet moves faster when it’s closer to the Sun (this closest point is called perihelion (PH)) and slower when it’s farther. K2L also tells us the force from the Sun is always attractive.
3. Kepler’s Third Law (K3L): Time, Size, and a Magic Number!
There’s a cool math connection between how long a planet takes to orbit the Sun once (its Period of Revolution (POR), or ‘T’) and the size of its orbit (the ‘average’ distance).
Simply put: T-squared divided by a-cubed is constant.
T² / a³ = k
This constant ‘k’ includes the Universal Gravitational Constant (UGC), or ‘G,’ which is the same everywhere.
K3L helps us calculate how long an orbit takes or how big its extent is.
