Cause: Orbit Geometry (Top View)
Sun
Target direction
Parallax axis
Target star
Baseline pending captures
Now
A
B
Earth motion changes the line-of-sight to the same star.
Live orbit drives detector shift. Captures freeze two epochs for inference.
Observable: Detector/Sky Shift
Now
A
B
Overlay mode: compare captured points directly.
Capture A and B to compute measured shift deltaTheta.
Background stars stay fixed while the apparent target position shifts.
Measured shift $\Delta\theta$
mas
Signed:
mas
Effective baseline $B_{\rm eff}$
AU
Chord:
AU | deltaPhi
deg
Inferred parallax $\hat p$
mas
arcsec
Equivalent Jan-Jul shift $2\hat p$ (derived)
mas
True distance (set) $d_{\rm true}$
pc
ly
Inferred distance (measured) $\hat d$
pc
ly
Signal-to-noise $\hat p/\sigma_{\hat p}$ (inferred)
Inferred parallax uncertainty $\sigma_{\hat p}$:
mas
Measurement quality
Inferred distance uncertainty $\sigma_{\hat d}$:
pc
What to notice
Model notes
Misconceptions
Cause:
Earth moves continuously, so the line-of-sight changes.
Observable:
the target shifts against fixed background stars on the detector.
Inference:
capture A and B, read $\Delta\theta$, then infer $\hat p$ and $\hat d$.
Distance relation: $d\,(\mathrm{pc}) = 1/p\,(\mathrm{arcsec})$.
General capture inference uses projected shift and effective baseline $B_{\rm eff}$.
Detector exaggeration changes only visualization, not computed $\hat p$ or $\hat d$.
Parallax is not star motion
; observer baseline changes drive the apparent shift.
Small effective baseline captures can make inference unstable even if the chord is large.
Larger measurement uncertainty $\sigma_{\rm meas}$ can dominate tiny shifts, weakening distance inference.