Why does Sirius proper motion “wiggle” with a 1 year period, when Sirius A and Bs binary orbit is a 50 year period?

Some stars, if observed repeatedly over time, show a perturbation or "wobble" in their proper motion. If this is a periodic occurrence we can infer that the perturbation occurs due to the gravitational influence of an unseen companion.

In Sirius Matters, Noah Brosch describes a secondary wiggle,

"The trajectory described by the two components of Sirius shows an additional component of motion as tiny wiggles super-posed on the wider modulations of the proper motion by the orbital motion of the Sirius pair. The wiggles have a period of one year. "

What causes this second wiggle?

• This version states "The wiggles . . . are a reflection of the motion of our vantage sight-point, the Earth". – HDE 226868 Dec 13 '16 at 15:09