Interactive tool

HR Diagram Explorer

Place a teaching point by surface temperature and luminosity, then distinguish a diagram region from a formal stellar classification.

Teaching estimate

Read the axes first

Temperature decreases from left to right in the conventional HR diagram. Luminosity is shown relative to the Sun on a logarithmic scale; the slider value is log10(L/Lsun). A point's diagram position is not a measured spectrum.

Use with care

  • The OBAFGKM label is only an approximate temperature band here.
  • Formal spectral type depends on absorption-line patterns, not temperature alone.
  • Evolutionary state also depends on radius, mass, composition, age, and uncertainty.
  • The broad region boundaries in this tool are deliberately simplified and must not be used for catalog classification.

Sources

Region labels, accessibility text, and limits reviewed 9 October 2026.

Compare with the star classification lab →

Signal interpretation console · tools

HR Diagram Explorer / observation pipeline

INPUT

Photons

Identify wavelength, exposure, field of view and observing date before reading the image.

STAGE A

Detector

Separate object signal from point-spread function, noise, saturation and selection.

STAGE B

Calibration

Track background removal, alignment, scaling and color mapping as part of the measurement.

OUTPUT

Physical claim

Connect “Read the axes first” to “Use with care” through an explicit model.

PRIMARY READOUT

Place a teaching point by surface temperature and luminosity, then distinguish a diagram region from a formal stellar classification.

MODEL WARNING

Color, spectrum, luminosity and evolutionary state are related but not interchangeable; distance and extinction shape where an object appears in a diagram. Projection, distance, extinction or adopted parameters may offer another explanation.

CROSS-CHECK

Query NASA Science: Stars and ESO: Hertzsprung-Russell diagram and seek an independent wavelength, spectrum, motion or catalogue measurement.

CONFIDENCE_PROTOCOL

For HR Diagram Explorer, label each statement as pixel-level observation, calibrated measurement, model-dependent inference or open hypothesis. Advance a claim only when the preceding stage is documented.