Tabby's star (KIC 8462852)Evidence
Evidence · Tabby's star (KIC 8462852)
The step survives on good-blue plates and runs against the colour-term trend
Restricted to plates DASCH classes as good blue (colour term -0.164 to 0.212), the target's post-1969 offset is 0.097 mag, above all 41 Gaia-screened matched stars (mean 0.010, sd 0.045, z = 1.9); within 1890-1953 the residuals do correlate with colour term (0.48 mag per unit, p = 1e-5), but the post-1969 plates' more negative terms would predict the star brighter, not fainter, so emulsion colour cannot make the step.
What it means
Key questionWhat causes the slow fading of the star?
Most likely: a large, diffuse amount of circumstellar dust, more extended than the clumps that make the dips
Most likelyunchanged
Openunchanged
Answer this evidence bears onThe century fade is a calibration artefact of plate photometry.
Counts against2 for, 3 against
Disputedunchanged
Next steps 1
1
Full per-plate differential with the Starglass platephot endpoint (needs a free API key): for each of the ~900 plates, pull every source within 10 arcmin and fit a plate zero-point from colour-matched stars within 5 arcmin of the target rather than 30 arcmin, then a hierarchical model with one zero-point per plate and one slope per star. Removes the position-dependent part of the plate systematics that the current 30-arcmin differential cannot.
~12 h
—not judged
Ranked by how likely each is to move the key question, for the time it takes
How it was found 1 run
Result. The offset is not an emulsion-colour effect: it is as large on good-blue plates as on all plates, the target is above every matched star either way, and the sign of the within-epoch colour-term dependence would make the post-1969 points brighter, not fainter..
Target offset by plate colour class; residual-vs-colour-term regression within epochs; target rank among matched stars on good-blue plates{'offset_all': 0.088, 'offset_blue_any': 0.093, 'slope_good_blue': 0.156, 'offset_good_blue': 0.097, 'matched_offset_all': {'n': 41, 'z': 1.64, 'sd': 0.047, 'mean': 0.012, 'target_percentile': 1}, 'slope_good_blue_err': 0.025, 'resid_vs_ct_1890_1953': {'n': 482, 'p': 1.1e-05, 'se': 0.108, 'slope': 0.48}, 'resid_vs_ct_1969_1990': {'n': 172, 'p': 0.36, 'se': 0.129, 'slope': -0.119}, 'target_points_by_class': {'unknown': 158, 'default0': 14, 'good_blue': 670, 'blue_other': 53}, 'matched_offset_good_blue': {'n': 41, 'z': 1.94, 'sd': 0.045, 'mean': 0.01, 'target_percentile': 1}, 'colour_term_median_pre1953': -0.015, 'colour_term_median_post1969': -0.132}The offset is not an emulsion-colour effect: it is as large on good-blue plates as on all plates, the target is above every matched star either way, and the sign of the within-epoch colour-term dependence would make the post-1969 points brighter, not fainter.
Sources 1
Cite it
Mysteries Department. (2026). The step survives on good-blue plates and runs against the colour-term trend [Evidence EVD0DEC1E9WNRJQ]. https://mysteriesdept.com/r/EVD0DEC1E9WNRJQ
@misc{mysteriesdept_evd0dec1e9wnrjq,
title = {The step survives on good-blue plates and runs against the colour-term trend},
author = {{Mysteries Department}},
year = {2026},
note = {Evidence, catalog key EVD0DEC1E9WNRJQ},
url = {https://mysteriesdept.com/r/EVD0DEC1E9WNRJQ}
}