The diagram does not make this clear at all, but the big circle is the orbit of the Moon. The Earth is only 12,756 km in diameter, and the tick marks are 200,00

The diagram does not make this clear at all, but the big circle is the orbit of the Moon. The Earth is only 12,756 km in diameter, and the tick marks are 200,000 km apart. If drawn to scale on that diagram, it would be 2.7 pixels wide.