ASTR 430 · Lecture 05

Lecture 05: Uncertainty Propagation and Calibration

Research Methods in Astronomy

A small formal error does not certify accuracy when a calibration term is shared across a sample.

Objectives and route

Terms for This Lecture

Jacobian

Definition: The matrix of partial derivatives that maps small input changes into output changes.

Why it matters here: In Uncertainty Propagation and Calibration, Jacobian is needed to reason about Jacobians, covariance, systematic offsets, and calibration transfer rather than merely label the phenomenon.

Relationship: It is interpreted alongside Covariance and the lecture relation below; identify which quantities are observed, calibrated, or model-derived.

Limitation or common confusion: The propagation is local; the offset is shared and is not independent noise.

\(C_y=J C_x J^T+C_sys\)

Why the method matters

A small formal error does not certify accuracy when a calibration term is shared across a sample.

Keep observation, calibration, transformation, model, and claim separate so each can be challenged.

systematic
Jacobians, covariance, systematic offsets, and calibration transfer. The geometry distinguishes inputs, transformations, and inferential limits.

Formal object

\(C_y=J C_x J^T+C_sys\)

Define fields, units, defaults, version identifiers, and the boundary between measured, adopted, and inferred quantities.

Read the evidence

Identify which part is input, transformation, and claim. A caption should let a reader reproduce the path without asking the author what was omitted.

systematic
Jacobians, covariance, systematic offsets, and calibration transfer. The geometry distinguishes inputs, transformations, and inferential limits.

Worked audit

For d=1/p, d=0.5 kpc and sigma_d≈0.0125 kpc; the stated zero point gives d=0.495786 kpc.

The propagation is local; the offset is shared and is not independent noise.

Estimate direction first, record units or decision criteria, then test one assumption. This check is generated from shared ASTR430 values.

Failure modes

Active reasoning

Prompt: For d=1/p, propagate 0.05 mas at p=2.0 mas and inspect a -0.017 mas zero-point shift.

What would you record so a skeptical collaborator could rerun or challenge the conclusion?

Paired workshop

The workshop turns this method into a reproducible artifact: a query manifest, screening log, uncertainty table, figure critique, time budget, or proposal review. The deliverable includes result and provenance.

Takeaways

Exact source anchors

Gaia EDR3 Documentation Chapters 4 and 8.

Archive, software, and ethics citations with verification status are in reference-log.md.