What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
Definition of post-main sequence in US English:
post-main sequence
adjective
AstronomyDesignating a star which is too old to lie within the main sequence on a Hertzsprung-Russell diagram, i.e. one which no longer has hydrogen fusion at its core and is relatively cool or dim, such as red giant.
Origin
1960s; earliest use found in Science.
