As an introductory example, to define a 5-meter orbit on an entity about the Y-axis that takes 10 seconds, we can offset the position and animate the rotation. This animation starts with the initial rotation about the Y-axis of 0 degrees, and goes around 360 degrees. It’s defined with a duration of 10000 milliseconds, maintains the final value on each cycle of the animation, and loops infinitely.
<a-entity position="5 0 0" rotation="0 0 0">
<a-animation attribute="rotation"
to="0 360 0"
dur="10000"
fill="forwards"
repeat="indefinite"></a-animation>
</a-entity>