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Jetlag & Health API

Compute social jetlag — the circadian cost of civil time misalignment with the Sun.

Background: The Roenneberg Formula

Till Roenneberg (LMU Munich) defined social jetlag as the discrepancy between biological clock time (anchored to the Sun) and civil clock time.

Key findings from Roenneberg et al. (2012):

  • ~69% of the Western population suffers >1h of social jetlag
  • Each extra hour of social jetlag increases obesity risk by 33%
  • Western edges of time zones have systematically worse health outcomes
  • China's single UTC+8 zone creates up to 3h of structural social jetlag in Xinjiang

TimeNow's /solar/jetlag endpoint computes the structural component — the permanent offset baked into the timezone assignment, not the seasonal DST component.

GET /solar/jetlag

Parameters

Parameter Required Type Description
lat ✅ float Latitude (−90 to +90)
lng ✅ float Longitude (−180 to +180)

Example

# Kashgar, China — one of the world's most extreme cases
curl "http://localhost:8090/solar/jetlag?lat=39.47&lng=75.99"

Response

{
  "latitude": 39.47,
  "longitude": 75.99,
  "timezone": "Asia/Kashgar",
  "utc_offset_h": 8,
  "solar_utc_offset_h": 5.07,
  "civil_solar_offset_min": -175,
  "jetlag_hours": 2.92,
  "risk_level": "severe",
  "risk_description": "Chronic misalignment of ~3h. Associated with significantly elevated cardiometabolic risk (Roenneberg 2012, Giuntella & Mazzonna 2019).",
  "percentile": 98
}

Response Fields

Field Type Description
civil_solar_offset_min float Minutes civil noon leads (+) or lags (−) solar noon
jetlag_hours float Absolute structural jetlag in hours
risk_level string low, moderate, high, severe
percentile int Percentile vs global population (98 = worse than 98% of Earth)

Risk Classification

risk_level jetlag_hours Description
low < 0.5h Negligible civil-solar offset
moderate 0.5–1.0h Within typical Western experience
high 1.0–2.0h Elevated risk; documented health effects
severe > 2.0h Extreme misalignment; strongly associated with metabolic disorders

References

  • Roenneberg T et al. Social Jetlag: Misalignment of Biological and Social Time. Current Biology 22(10):939–943, 2012.
  • Roenneberg T, Merrow M. The Circadian Clock and Human Health. Current Biology 26(10):R432–R443, 2016.
  • Giuntella O, Mazzonna F. Sunset time and the economic effects of social jetlag. Journal of Health Economics 65:210–226, 2019.