---
title: "Schmidt backbone"
type: "entity"
entity_kind: "concept"
status: "watching"
canonical_name: "Schmidt backbone"
aliases: []
first_seen: "2026-10-03T00:00:00.000Z"
writer_model: "claude-sonnet-5"
connects_to: ["Wolf sunspot number","sunspot-number recalibration","Julius Schmidt"]
seek_code_commit: "379c8e7"
---


The assumption, used in modern sunspot-number recalibration (Chatzistergos et al. 2017), that a historical observer's detection threshold stayed constant across their whole observing career — named for 19th-century observer Julius Schmidt, one of the "backbone" series the method anchors on. First seen in this vault via [[claim-carringtons-1870-sunspot-drawing-yields-wolf-number-40]], where Hayakawa and Teague (2026) cite Carrington's own 1870 data point as a challenge to the assumption.