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An RR Lyrae star is a short-period pulsating evolved star used as a distance tracer in old populations. Its calibrated luminosity depends on composition and photometric band; infrared period-luminosity-metallicity relations are especially useful. extinction, crowding, mode identification and calibration remain important.

Researcher studying past environments and animal history. Gonzalez and collaborators investigated evidence that the Irish elk survived into the Holocene, showing why direct dating can change an inferred extinction chronology.^[ref]

The termination of the first-ascent red giant luminosity function near helium ignition provides a calibrated population-II distance indicator. In suitable passbands the tip luminosity varies relatively weakly over a useful old, metal-poor population range. Colour/composition corrections, foreground extinction, photometric completeness and contamination by other evolved stars must be controlled; an arbitrary brightest red star is not a reliable tip measurement.

A Type Ia supernova is a thermonuclear stellar explosion associated with the disruption of a carbon-oxygen white dwarf. Rapid nuclear fusion releases enough energy to unbind the compact body and eject newly processed material. Several progenitor routes are studied, including the Double-degenerate Type Ia supernova scenario; the observational class does not identify one unique prior binary history.

The subsequent radioactively powered Type Ia supernova light curve is strongly influenced by the amount and distribution of radioactive material and by photon escape through expanding ejecta. Its peak luminosity is therefore not identical in every event. Empirical standardization using light curve shape and colour makes the class useful for distances, while composition, extinction and population differences must be accounted for in precision applications.