Learning goals

• Draw a circle with a chosen radius.
• Explain where the turtle starts when it draws a circle.
• Move the turtle so a circle is centered at a chosen position.

You can draw a circle with circle(radius). The radius is the distance from the center of the circle to its edge.

otto.circle(50)

This draws a circle with a radius of 50. The turtle walks around the circle and ends up where it started.

Where does the circle appear?

The turtle does not start in the middle of the circle. It starts at the bottom of the circle. The turtle draws the circle counterclockwise. That means it turns to the left, like the hands of a clock going backwards. So the middle of the circle is radius steps above the turtle.

To draw a circle with its center at (0, 0), first move the turtle to the bottom of that circle. That is radius steps below the center. Lift the pen so you do not draw a line on the way:

otto.penup()
otto.goto(0, -50)
otto.pendown()
otto.circle(50)

Example: a snowman

A snowman is a big circle with a small circle on top. This program draws one:

import turtle as otto

otto.penup()
otto.goto(0, -100)
otto.pendown()
otto.circle(50)

otto.penup()
otto.goto(0, 0)
otto.pendown()
otto.circle(30)

1. The turtle goes to (0, -100) and draws the big circle. The turtle starts at the bottom of the circle.
2. The big circle is 100 steps high. So its top is at (0, 0).
3. The turtle goes to (0, 0) and draws the small circle on top.

Summary