Why ISS will not move with linear motion?

Goodmorning everyone,
I would like to understand why the movement of the ISS (or in my opinion seems) vibrating:
It seems that it moves jerkily, not a linear movement.
This can be observed both to the naked eye, using one of the many sites that transmit the USTREAM channel of the station.

Thanks a lot!

IU1AKG Fabrizio

IU1AKG – Wed, 2016 – 06 – 22 04:46

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