He noticed that the apparent position of the star changed as the Earth moved around its orbit.
Of course, to be considered a planet in our Solar System, unlike Pluto, it would have to clear the neighborhood around its orbit.
As it moves around its orbit, Venus displays phases like those of the Moon in a telescopic view.
Far around its orbit, too distant to interfere directly, preoccupied with local problems, and unable to send a large battle fleet.
It must have cleared the neighbourhood around its orbit.
Seen from the Earth, it appears to move around its orbit in about 116 days, which is much faster than any other planet.
I know you have cameras spotted all around your orbit.
We will assume that on Earth the limiting distance is two feet; around Mars's orbit, some miles; between stars, a few light minutes.
One of the main points at issue is the precise meaning of "cleared the neighbourhood around its orbit".
They say that Pluto does not qualify as a planet under the new definition because it has not cleared the neighborhood around its orbit.