Stars & the cosmos · START WITH SOMETHING FAMILIAR
Why does a sky measurement need a laboratory reference?
FIRAS’s external calibrator was a shaped absorber made from iron-loaded epoxy. It could fill the instrument’s sky aperture, giving a controlled reference observed through the same measurement system. Its reflectance, temperature gradients and leakage had to be characterized. The iron and carbon links describe the reference material; they are not chemical species inferred from the cosmic spectrum.
The original analysis includes frequency correlations. The published approximation gives neighboring bins a correlation of 0.176 and bins two steps apart −0.203.
Explore the model (optional)
OBSERVATION & MODEL
These are published observations after calibration and foreground modeling. NASA’s intensity column combines a 2.725 K reference blackbody with measured residuals. Moving temperature changes only the comparison model.
The intensity scale is fixed. The small uncertainties become visible in the residual plot below.
The vertical range adapts to the current and saved comparisons. Error bars describe the archived bins, which are correlated.
RMS summarizes the displayed reference-relative differences. It is not a fit probability or a temperature confidence interval: neighboring bins are correlated, and the archive already uses a fitted reference.
r(T) = r_archive + Bν(2.725 K) − Bν(T)
Residuals and errors in the source table are kJy/sr; divide by 1000 for MJy/sr. We preserve the archived residual exactly at 2.725 K. Recalculating the original baseline with modern SI constants at the printed wavenumbers differs by up to 0.007598 MJy/sr, so this is explicitly a reference-relative comparison.
Bν = (2hν³/c²) / [exp(hν/kT) − 1], with ν = 100cw for w in cm⁻¹. The galaxy template is not subtracted again. The later published 2.72548 K temperature combines other evidence and is not a value this table independently recovers.
| cm⁻¹ | Intensity MJy/sr | Residual kJy/sr | 1σ kJy/sr | Galaxy model kJy/sr | Current difference MJy/sr |
|---|---|---|---|---|---|
| 2.27 | 200.723 | 5 | 14 | 4 | 0.005000 |
| 2.72 | 249.508 | 9 | 19 | 3 | 0.009000 |
| 3.18 | 293.024 | 15 | 25 | -1 | 0.015000 |
| 3.63 | 327.77 | 4 | 23 | -1 | 0.004000 |
| 4.08 | 354.081 | 19 | 22 | 3 | 0.019000 |
| 4.54 | 372.079 | -30 | 21 | 6 | -0.030000 |
| 4.99 | 381.493 | -30 | 18 | 8 | -0.030000 |
| 5.45 | 383.478 | -10 | 18 | 8 | -0.010000 |
| 5.9 | 378.901 | 32 | 16 | 10 | 0.032000 |
| 6.35 | 368.833 | 4 | 14 | 10 | 0.004000 |
| 6.81 | 354.063 | -2 | 13 | 12 | -0.002000 |
| 7.26 | 336.278 | 13 | 12 | 20 | 0.013000 |
| 7.71 | 316.076 | -22 | 11 | 25 | -0.022000 |
| 8.17 | 293.924 | 8 | 10 | 30 | 0.008000 |
| 8.62 | 271.432 | 8 | 11 | 36 | 0.008000 |
| 9.08 | 248.239 | -21 | 12 | 41 | -0.021000 |
| 9.53 | 225.94 | 9 | 14 | 46 | 0.009000 |
| 9.98 | 204.327 | 12 | 16 | 57 | 0.012000 |
| 10.44 | 183.262 | 11 | 18 | 65 | 0.011000 |
| 10.89 | 163.83 | -29 | 22 | 73 | -0.029000 |
| 11.34 | 145.75 | -46 | 22 | 93 | -0.046000 |
| 11.8 | 128.835 | 58 | 23 | 98 | 0.058000 |
| 12.25 | 113.568 | 6 | 23 | 105 | 0.006000 |
| 12.71 | 99.451 | -6 | 23 | 121 | -0.006000 |
| 13.16 | 87.036 | 6 | 22 | 135 | 0.006000 |
| 13.61 | 75.876 | -17 | 21 | 147 | -0.017000 |
| 14.07 | 65.766 | 6 | 20 | 160 | 0.006000 |
| 14.52 | 57.008 | 26 | 19 | 178 | 0.026000 |
| 14.97 | 49.223 | -12 | 19 | 199 | -0.012000 |
| 15.43 | 42.267 | -19 | 19 | 221 | -0.019000 |
| 15.88 | 36.352 | 8 | 21 | 227 | 0.008000 |
| 16.34 | 31.062 | 7 | 23 | 250 | 0.007000 |
| 16.79 | 26.58 | 14 | 26 | 275 | 0.014000 |
| 17.24 | 22.644 | -33 | 28 | 295 | -0.033000 |
| 17.7 | 19.255 | 6 | 30 | 312 | 0.006000 |
| 18.15 | 16.391 | 26 | 32 | 336 | 0.026000 |
| 18.61 | 13.811 | -26 | 33 | 363 | -0.026000 |
| 19.06 | 11.716 | -6 | 35 | 405 | -0.006000 |
| 19.51 | 9.921 | 8 | 41 | 421 | 0.008000 |
| 19.97 | 8.364 | 26 | 55 | 435 | 0.026000 |
| 20.42 | 7.087 | 57 | 88 | 477 | 0.057000 |
| 20.87 | 5.801 | -116 | 155 | 519 | -0.116000 |
| 21.33 | 4.523 | -432 | 282 | 573 | -0.432000 |
Every non-comment row from NASA’s released table, in original order. No points were added or removed. The download page dates delivery to March 2003; the file header dates its initial revision to May 2005. Both are preserved in our source record.
SHA-256: df793c3dca09ebfa7dbc5aa0ec1951daa8884431bc30eff28a710d7516cf50fa
MAKE THE CONNECTION
Several neighboring residuals form a pattern. What is the strongest justified next step?
HISTORY THROUGH EVIDENCE
The archive provides 43 wavenumbers, a reconstructed intensity, measured residuals, uncertainties and a Galactic model column.
Explore how the evidence changed the explanation →ANOTHER HISTORICAL INVESTIGATION
1925–1929 · Reveal observations and weigh an interpretation.
Open the evidence desk →WORK WITH MEASURED EVIDENCE
A source spectrum and a detector threshold together determine what can be observed.
Compare light evidenceResolved atomic lines and a thermal continuum carry different kinds of information.
