In astrophysics

Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...

, the Phillips relationship is the relationship between the peak luminosity of a Type Ia supernova

Type Ia supernova

A Type Ia supernova is a sub-category of supernovae, which in turn are a sub-category of cataclysmic variable stars, that results from the violent explosion of a white dwarf star. A white dwarf is the remnant of a star that has completed its normal life cycle and has ceased nuclear fusion...

 and the speed of luminosity evolution after maximum light. During the course of the Calán/Tololo Supernova Survey, Mark M. Phillips

Mark M. Phillips

Mark M. Phillips is internationally recognized astronomer in the observational studies of all classes of supernovae. He is well known for his work on SN1986G, SN1987A, the Calán/Tololo Supernova Survey, the High-Z Supernova Search Team, and especially for the Phillips relationship...

 discovered that the faster the supernova faded from maximum light, the fainter its peak magnitude was. It has been recast to include the evolution in multiple photometric bandpasses and as a stretch in the time axis relative to a standard template.
The relation is typically used to bring any Type Ia supernova peak magnitude to a standard candle value.

It was originally defined as the decline in the B-magnitude light curve

Light curve

In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band...

 from maximum light to the magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

15 days after B-maximum, a parameter he called .