Annual stellar parallax and distance
Changing observing position permits geometric distance inference.
Key knowledge
Annual stellar parallax is apparent angular displacement caused by the observer's orbital baseline. With the conventional one-AU parallax baseline, distance in parsecs is the reciprocal of parallax in arcseconds. Reliable measurement requires separating parallax from other apparent motions and instrument effects.
Values and equations
d / pc = 1 / (p / arcsec)
- d
- geometric stellar distance pc
- p
- annual parallax semiamplitude arcsec
Conditions and scope
- The formula uses the annual parallax semiamplitude, not the full displacement between opposite orbital positions.
- Direct inversion is useful for sufficiently precise, corrected positive parallaxes; noisy measurements require uncertainty-aware inference.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected reciprocal-parallax relation and ESA orbital-baseline geometry.
2026-10-10 · Checked baseline, angular units and measured-distance qualification; no Gaia catalogue reanalysis.
Entry details
Permanent link to this entry ↗- Record identity
- cosmos-parallax-distance
- Revision
- university-reference.1
- Structured reference record
- University reference