A diagram involving → formal compactification of
→ space-time used in → general relativity
to describe the causal properties of the space-time.
Only two of the space dimensions are shown and horizontal lines represent space,
while vertical lines belong to time. The → null geodesicss are at 45Â°, which
facilitates the visualization of → light cones. The major feature of
Penrose-Carter diagram is representing the whole space-time on a
finite surface, while putting → spacelike and
→ timelike infinities at finite distance.

Named for Roger Penrose (1931-) and Brandon Carter (1942-) who introduced it
independently; → diagram.

phase diagram

نمودار ِ فاز

nemudâr-e fâz

Fr.: diagramme de phases

A graph showing the equilibrium relationships between
phases (such as vapor-liquid, liquid-solid) of a chemical compound,
mixture of compounds, or solution.

A simple way of representing the → space-time continuum,
usually including time and only one spatial dimension. The curve of a particle's
equation of motion on a space-time diagram is called a → world line.
Same as → Minkowski diagram.

Fr.: diagramme spectroscopique de Hertzsprung-Russell

A spacial → Hertzsprung-Russell diagram (HRD)
which is independent of distance
and extinction measurements. The sHRD is derived from the classical HRD
by replacing the luminosity (L)
to the quantity ℒ = T^{ 4}_{eff}/g
which is the inverse of the flux-weighted gravity
introduced by Kudritzki et al. (2003). The value of ℒ can be
calculated from stellar atmosphere analyses without prior knowledge
of the distance or the extinction. In contrast to the classical
T_{eff}-log g diagram
(→ Kiel diagram), the sHRD sorts stars according
to their proximity to the → Eddington limit,
because ℒ is proportional to the
Eddington factor Γ = L/L_{Edd} according to
the relation
ℒ =
(1/4πσG)(L/M) = (c/(σκ)Γ,
where σ is the → Stefan-Boltzmann constant,
κ is the electron → scattering
→ opacity
in the stellar envelope, and the other symbols
have their usual meanings
(Langer, N., Kudritzki, R. P., 2014, A&A 564, A52, arXive:1403.2212,
Castro et al., 2014, A&A 570, L13.

A schematic diagram using circles to represent sets
and the relationships between them. Each circle represents one set. Two or more
may be overlapped. The areas of overlap indicate subsets.

Named after John Venn (1834-1923), a British logician and philosopher, who introduced
the diagram; → diagram.