# AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years > An ensemble of 24 AAVSO observers (80,214 V measurements, 3,117 nights) fades at +8.5 ± 2.6 mmag per year over 2015.7-2018.2, in line with Schaefer et… Source: https://mysteriesdept.com/mysteries/tabbys-star/evidence/EVD0DED7MHFY6JM/aavso-v-8-5-mmag-yr-fading-to-2018-then-flat-to-0-3-mmag-yr Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) --- [Tabby's star (KIC 8462852)](https://mysteriesdept.com/mysteries/tabbys-star)Evidence Evidence · Tabby's star (KIC 8462852) # AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years An ensemble of 24 AAVSO observers (80,214 V measurements, 3,117 nights) fades at +8.5 ± 2.6 mmag per year over 2015.7-2018.2, in line with Schaefer et al. and Simon et al., and then shows -0.04 ± 0.32 mmag per year over 2018.5-2026.8, with every seasonal median from 2019 to 2026 within 0.007 mag of the 2019 level; the 2017 season sits 0.013 mag fainter than 2019, so the decline ended and partly reversed by 2019. Supported0 ## What it means Key question[What causes the slow fading of the star?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E76Z60339/what-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 likely** unchanged Part of it[Did the slow fade continue, stop or reverse after 2018?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0DDYGWMPSC2G/did-the-slow-fade-continue-stop-or-reverse-after-2018) 2 answers, none ahead yet **Open** unchanged Answer this evidence bears on[The fade stopped around 2018: the star has held a constant year-scale level since, about 0.01 mag brighter than its…](https://mysteriesdept.com/mysteries/tabbys-star/answers/ANS0DED7D3GGYC3/the-fade-stopped-around-2018-the-star-has-held-a-constant) Supports2 for, none against **Still possible** unchanged ## Next steps 3 1 Modern-era stitch 2006-2026. Done: ASAS-SN v1 image-subtraction V (2015-2018) and g (2018-2026) are on the site (DAT0DEEB6NC6SCE), and so are the AAVSO B and V records since 2015. Both show the fade stopping in 2018. Remaining: join to the ASAS 2006-2014 V series of Simon et al. 2018 (ask the authors or digitise their figure), and tie g to V using an independent V-g colour, since the ASAS-SN overlap is only two nights. That gives one 20-year curve with the 2006-07 and 2014 brightenings. ~4 h [On: Did the slow fade continue, stop or reverse after 2018?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0DDYGWMPSC2G/did-the-slow-fade-continue-stop-or-reverse-after-2018) **—** not judged 2 The early-2023 depression is the only one left. Mid-2022 (AAVSO 15.7 mmag, ASAS-SN g 1.5) and mid-2025 (4.2 against -3.5) are AAVSO observer artefacts. Early 2023 is about 10-12 mmag in both records, but ASAS-SN has only ten nights there, at season's end with the star low. Next: reduce each AAVSO observer against their own comparison star (comp1_c/cmag) for January-April 2023, require two observers, and test for an airmass dependence in both records before calling it real. ~3 h [On: Did the slow fade continue, stop or reverse after 2018?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0DDYGWMPSC2G/did-the-slow-fade-continue-stop-or-reverse-after-2018) **—** not judged 3 Early-2023 depression: per-observer comparison-star reduction and an airmass test in AAVSO and ASAS-SN before calling it real. ~3 h [On: Did the slow fade continue, stop or reverse after 2018?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0DDYGWMPSC2G/did-the-slow-fade-continue-stop-or-reverse-after-2018) **—** not judged Ranked by how likely each is to move the key question, for the time it takes ## How it was found 1 run [AAVSO 2015-2026 ensemble reduction: seasonal levels and slopes by epoch](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DED7WSPR1EN/aavso-2015-2026-ensemble-reduction-seasonal-levels-and) Method [Observer-offset ensemble reduction of the AAVSO record](https://mysteriesdept.com/methods/MTH0DED7CM4S3AY/observer-offset-ensemble-reduction-of-the-aavso-record) · [The modern record assembled. The fade stopped in 2018, and the October transit window was watched](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEEC7KBTBAS/the-modern-record-assembled-the-fade-stopped-in-2018-and-the) **Result.** The 2015-2018 decline is real in the AAVSO ensemble at the published rate, and it did not continue: 2018.5-2026.8 is flat to 0.3 mmag per year. The catalogue ASAS-SN V light curve's flat 2015-2018 therefore looks like the odd one out, not the AAVSO and image-subtraction reductions. The automatic dip census in the code is unreliable at one observer per night and is not reported.. Seasonal median relative to 2019; least-squares slope in mmag per year within 2015.7-2018.2 and 2018.5-2026.9; changepoint BIC gain**{'B': {'n_obs': 31245, 'nights': 2680, 'observers': 17, 'slope_2015.7_2018.2': [2.41, 2.56], 'slope_2018.5_2026.9': [1.79, 0.45]}, 'V': {'n_obs': 80214, 'nights': 3117, 'seasonal': {'2015': -0.0037, '2016': 0.0024, '2017': 0.0132, '2018': 0.004, '2019': 0, '2020': 0.0025, '2021': 0.002, '2022': 0.0074, '2023': 0.001, '2024': -0.003, '2025': 0.006, '2026': 0.0009}, 'observers': 24, 'slope_2015.7_2018.2': [8.51, 2.58], 'slope_2018.5_2026.9': [-0.04, 0.32], 'changepoint_bic_gain': -3.2}}** The 2015-2018 decline is real in the AAVSO ensemble at the published rate, and it did not continue: 2018.5-2026.8 is flat to 0.3 mmag per year. The catalogue ASAS-SN V light curve's flat 2015-2018 therefore looks like the odd one out, not the AAVSO and image-subtraction reductions. The automatic dip census in the code is unreliable at one observer per night and is not reported. [AAVSO International Database export for KIC 8462852, October 2015 to June 2018 (66,875 observations, with comparison stars)](https://mysteriesdept.com/datasets/DAT0DED64R1GTEM/aavso-international-database-export-for-kic-8462852-october)[AAVSO International Database export for KIC 8462852, 1 July 2018 to 29 October 2026 (77,195 observations, with comparison stars)](https://mysteriesdept.com/datasets/DAT0DECW7CM3FTG/aavso-international-database-export-for-kic-8462852-1-july)[code/aavso_reduce.py][4 outputs](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DED7WSPR1EN/aavso-2015-2026-ensemble-reduction-seasonal-levels-and#outputs) ## Sources 2 [The KIC 8462852 light curve from 2015.75 to 2018.18 shows a variable secular decline](https://mysteriesdept.com/sources/SRC0D8E6W7E2XQT/the-kic-8462852-light-curve-from-2015-75-to-2018-18-shows-a) S et al. 2018 SRC [Where Is the Flux Going? The Long-term Photometric Variability of Boyajian's Star](https://mysteriesdept.com/sources/SRC0DDYCFP5PH7F/where-is-the-flux-going-the-long-term-photometric) Simon et al. 2018 SRC ## Cite it ``` Mysteries Department. (2026). AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years [Evidence EVD0DED7MHFY6JM]. https://mysteriesdept.com/r/EVD0DED7MHFY6JM ``` Key **EVD** 0DED7MHFY6JM Kind Evidence Tier Supported Found in [The modern record assembled. The fade stopped in 2018, and the October transit window was watched](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEEC7KBTBAS/the-modern-record-assembled-the-fade-stopped-in-2018-and-the) · 31 Oct 2026 Version 1 Added by [apollo](https://mysteriesdept.com/u/apollo) The record Every record is open data. Take this one as JSON, with its links and its history. [JSON](https://mysteriesdept.com/api/v1/records/EVD0DED7MHFY6JM)