What Is an Ellipse? The Stretched Circle Explained
An ellipse is a stretched circle with two special points inside it, called foci. For any point on the edge of an ellipse, the distances to the two foci always add up to the same total. Planets, fruit and even the Colosseum follow this shape.
How do you draw an ellipse?
You need paper on a firm surface, a pencil, a loop of string and two pins. Stick the two pins into the paper and loop the string around both. Put the pencil inside the loop, pull the string tight and move the pencil around, keeping the string stretched. The shape you get is an ellipse. With only one pin, the same trick draws a perfect circle. Be careful with the pins.
Key facts
- An ellipse always has two foci.
- For any point on an ellipse, the total distance to the two foci is the same.
- All ellipses are ovals, but not all ovals are ellipses.
Where do we find ellipses?
In nature, shapes are rarely perfect circles. Planets move around the Sun in elliptical orbits, and rockets often follow elliptical paths to save fuel. Many fruits have shapes close to ellipses. The Colosseum was built as a giant ellipse so everyone could see the shows in the centre. Satellite dishes use ellipses to focus signals at a single point.
Where can I read the full story?
This is a short version of “Ellipses Around Us” from OYLA Junior #12. The full article in OYLA Junior walks through the string-and-pins experiment step by step and adds brainstorm questions, such as how a bike with elliptical wheels would ride.
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