Flux calibration and magnitude uncertainty
Photometric counts need a calibrated band response and zero point before they represent an astronomical flux or magnitude.
Key knowledge
Photometric counts need a calibrated band response and zero point before they represent an astronomical flux or magnitude. For positive flux F with small standard uncertainty u(F), first-order propagation through m=−2.5log₁₀F+C gives u(m)≈[2.5/ln10]u(F)/F. Calibration and extinction uncertainties remain separate contributions.
Values and equations
u(m) ≈ (2.5/ln 10)u(F)/F
- u(m)
- magnitude standard uncertainty mag
- F,u(F)
- positive flux and its standard uncertainty same flux units
Conditions and scope
- The logarithm is shorthand for a ratio to the specified flux reference; use one band and magnitude convention.
- The symmetric linear approximation can fail near zero flux or at low SNR; it does not turn a negative measured background-subtracted count into a physical logarithmic magnitude.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the logarithmic flux transformation. The displayed uncertainty is a disclosed derivative-based small-error result, rather than the page's finite asymmetric difference or its rounded 1/SNR approximation.
2026-10-10 · Independent AI editorial review: All44 exact root-authored compact records, equations/variable units/conditions and140 origin edges accepted after independently reading final6/18 with bounded primary bodies and matching prior38/122 scientific fingerprints unchanged. Exact claim/edge review is distinct from combined inventory scope and separate CLE26 approval; no entire cited books or old-corpus experimental revalidation is asserted. Receipt: cosmos-completion-independent-content-and-inventory-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-cosmos-photometric-uncertainty
- Revision
- core.1
- Structured reference record
- University core expansion