If the planet is following a circular orbit, you need to know the center of the circle, the radius, and the axis of rotation. In your case, the axis of rotation is the y-axis. Therefore the points on along orbit can be computed by the trigonometric functions `sin`

and `cos`

Define a center point (`float CPT[3]`

) and a radius (`float radius`

). Use the Line primitive type `GL_LINE_LOOP`

to draw the circular orbit:

```
glBegin(GL_LINES);
for (float angle = 0; i < 2 * PI; angle += 0.01)
{
float x = CPT[0] + cos(angle) * radius;
float y = CPT[1];
float z = CPT[2] + sin(angle) * radius;
glVertex3f(x, y, z);
}
glEnd();
```

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