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# H-R Diagram

H-R Diagram
Hertzsprung-Russell diagram. A diagram of stars arranged according to their luminosity (measured on the y axis) and temperature (on the x axis). In the early part of the twentieth century, the Danish astronomer E.

: The H-R (Hertzsprung-Russell) diagram is used by astronomers to classify stars according to their luminosity, spectral type, color, temperature and evolutionary stage.

H-R diagram
Hertzsprung-Russell diagram; a plot of the luminosity (or absolute magnitude) of stars against their surface temperature (or spectral type).

A plot of the intrinsic brightness versus the surface temperature of the stars. It separates the effects of temperature and surface area versus spectral type, but also luminosity versus surface temperature or color.
Half-Life ...

H-R Diagram
The Color-Magnitude Diagram is a graph upon which stars are plotted by spectral type and actual luminosity. It is named for the two scientists Russell and Hertzsprung who first used it in 1913.

from Helium Burning to White Dwarf.
7. Helium Burning Main Sequence ...

H-R Diagrams can be used in a variety of stellar applications. A few of them are discussed below.
Classification ...

The Hertzsprung -Russell (H-R) Diagram is a graph that plots stars color (spectral type or surface temperature) vs. its luminosity (intrinsic brightness or absolute magnitude).

H-R Diagrams
Main Sequence & Nucleosynthesis
Post-Main Sequence
Solar Mass Star Death
High Mass Star Death
Star Clusters
H-R Diagram Activities
Stellar Evolution Questions
The Life & Death of Stars ...

: A graph that uses two stellar properties, such as luminosity versus surface temperature, as its axes.

H-R diagram
 Notes
^ a b c d e f g These proportions are fractions of stars brighter than absolute magnitude 16; lowering this limit will render earlier types even rarer while generally adding only to the M class.

An , also know as the Hertzsprung-Russell diagram, is of great importance in the study of stellar evolution. It is a two-dimensional graph that demonstrates the correlation between the spectral type, temperature and luminosity of stars.

The H-R diagram is also called a color-magnitude diagram because the absolute magnitude is usually plotted vs. the color.

In an for a cluster of stars, the point where the main sequence turns off toward the upper right. The main-sequence turn-off, showing which stars in the cluster have evolved to become red giants, is an indicator of the age of the cluster.

Once the H-R diagram was popularized, a new method of determining the distances to stars was found - that of spectroscopic parallax. Actually, this is a rather confusing term, since there is no parallax angle measured.

A composite . The magnitudes and temperatures (measured by photometry) of stars in several star clusters are plotted. The position of a group of points in the diagram can tell us how old that particular star cluster is.

Determined by H-R diagrams and stellar models; color and luminosity of stars leavingmain sequence is a measure of age.
albedo ...

Figure: An showing the evolutionary track for a one solar massed star.

The Hertzsprung-Russell diagram, or simply the H-R diagram, plots star color along the horizontal axis and luminosity along the vertical axis. To make the chart fit on a single page, we actually plot the log10 of the luminosity.

Highly Polarized Quasar

See Hertzsprung-Russell Diagram. [C95]
HRS ...

Large, cool, highly luminous stars in the upper right of the H-R diagram. Typically 10-100 times the diameter of the sun.
Glacial Period
Time when glaciers advance and engulf huge sheets of land
Glitch
A sudden change in the period of a pulsar.

main sequence Major distributional segment of the stars running diagonally across the from the upper left to the lower right.

The significance of the H-R diagram is that stars are concentrated in certain distinct regions instead of being distributed at random. This regularity is an indication that definite laws govern stellar structure and stellar evolution.

When stars are burning hydrogen to helium in their cores, they fall on a single curve in the luminosity-temperature plot known as the after its inventors, Hertzsprung and Russell.

The H-R Diagram provides astronomers the stellar "big picture," a handful of conceptual hooks on which to hang billions of stars. The most prominent feature is the main sequence, where stars spend the majority of their luminous life.

As its name implies, the horizontal branch is a horizontal, linear feature seen in cluster s, meaning that stars on the horizontal branch all have similar luminosities, but can have a range of effective temperatures.

These are supergiants in the instability strip on the H-R diagram, undergoing regular pulsations that are expressed by luminosity and temperature variations.

Of spectral and luminosity type B8 -- previously A5-F0 -- IIpe (Grady et al, 1996, in pdf, page 176), this star is still contracting towards the main sequence (see for pre-main sequence tracks for seven stars of different mass).

Ages for star clusters can be estimated by comparing the H-R diagram for the cluster with theoretical models of stellar evolution, and using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated.

Stars that began with more than six times the Sun's mass then evolve left and right through complicated loops on the as if in a frenzy to keep up their energy production, then finally explode as supernovae.

main-sequence turnoff Special point on an H-R diagram for a cluster. If all the stars in a particular cluster are plotted, ...

A new star will fall at a specific point on the main sequence of the .

asymptotic giant branch Path on the H-R diagram corresponding to the changes that a star undergoes after helium burning ceases in the core.

A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (), allows the current age and evolutionary state of a particular star to be determined.

instability strip: The region of the H-R diagram in which stars are unstable to pulsation; a star passing through this strip becomes a variable star.
intercloud medium: The hot, low-density gas between cooler clouds in the interstellar medium.

Isochrone - Lines in an occupied by stars of different masses but the same age
Isotopes - Nuclei with the same number of protons but different numbers of neutrons
Isotropic - Looking the same in all directions ...

Hertzsprung and Russel introduce H-R diagram that shows how the characteristics of stars are related.
1914 A.D.
U.S.A.

Hertzsprung-Russell Diagram ()
A plot of luminosity versus temperature for a group of stars.

T graph (AKA the Hertzsprung-Russell or H-R diagram), it's known as the "instability strip." Other variable stars (including the Mira variables and the RR Lyrae variables) fall along different parts of this strip.

lives, when stars burn hydrogen in their core, there's a clear and simple relationship between a star's color and brightness. Nearly a century ago, astronomers developed a way to illustrate this relationship with what's now called the , ...