In the simple Earth–Sun–star diagram, stellar parallax p uses the one-AU Earth–Sun baseline and is half the ideal two-view angle from opposite orbital viewpoints. These viewpoints change a nearby star’s apparent position relative to more distant stars.

Because stellar parallax angles are tiny, small-angle geometry gives p (radians) ≈ baseline/distance, with both lengths in matching units. Equivalently, d (pc) ≈ 1/p (arcsec). Keep these angular units consistent with the chosen formula.

Apparent displacement decreases with distance, and even nearby shifts are tiny. Analyst deduction: measuring such shifts depends on angular resolution; the supplied evidence gives no universal distance cutoff.

Primary sources:

• https://www.astro.ucla.edu/~wright/distance.htm
• https://www.esa.int/Science_Exploration/Space_Science/Gaia/Parallax