(degree) To a detectable degree, sufficient to be observed.As the planet orbits the star, it causes a wobble in the star's motion, which can be detected as a small but observably large Doppler effect.
(manner) In an observable manner.From the point of view of earth-based observatories, the effect of the planet's orbit around the star is that the star observably wobbles.
(modal) Indicates that the proposition can be verified by observation.Observably, the star wobbles.
