H–R diagram — Science definition
A diagram comparing stellar luminosity and surface temperature or spectral class.
Where it is taught
- Star Properties & H–R Diagrams — Stars & the Universe, Earth & Space Science, Grade 9
In use
An H–R diagram compares stellar luminosity with surface temperature.
Star Properties & H–R Diagrams
Questions using h–r diagram
Problem 1
Hints
Luminosity is intrinsic output, distinct from apparent brightness.
Answer and explanation
It likely has a large radiating surface, consistent with a giant or supergiant region rather than a small main-sequence star.
Problem 2
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Many diagrams place hot temperatures on the left, opposite the usual increasing numerical axis.
Problem 3
- distance
- temperature or colour
- age
- mass only
Answer and explanation
temperature or colour
Temperature runs along the horizontal axis, conventionally hottest on the left.
Problem 4
Answer and explanation
Luminosity depends on both surface temperature and surface area. Two stars at the same temperature emit the same energy per unit area, so the one far more luminous must have a much larger surface. Reading a star's position on the diagram therefore gives its radius relative to others, which is an inference from two measurable quantities rather than a direct measurement.
Response criteria
- State a scientifically accurate conclusion.
- Show the data, mechanism, or calculation that supports it.
- Include units, conditions, or limits where relevant.