The three main groups of stars on the Hertzsprung-Russell (HR) diagram are main sequence stars, red giants, and white dwarfs. Main sequence stars, which comprise the majority of stars, fuse hydrogen into helium in their cores and are found along a diagonal band from the upper left to the lower right. Red giants, located in the upper right, are evolved stars that have expanded and cooled after exhausting their hydrogen. White dwarfs, found in the lower left, are remnants of stars that have shed their outer layers and are no longer undergoing fusion.
The location on the Hertzsprung-Russell (HR) diagram where most stars lie is known as the main sequence. The HR diagram is a plot of stellar luminosity against surface temperature. The main sequence is a prominent band that extends diagonally across the HR diagram from high temperature and high luminosity to low temperature and low luminosity. The majority of stars, approximately 90% of all stars, are situated along the main sequence on the HR diagram. These stars are often referred to as main-sequence stars. They exhibit a smooth relationship between surface temperature and luminosity, with varying sizes and masses but sharing this common characteristic of lying on the diagonal band from the upper left to the lower right of the HR diagram. Source: Teach Astronomy - The Hertzsprung-Russell Diagram
The majority of stars in a Hertzsprung-Russell (HR) diagram are located along the main sequence, which runs diagonally from the upper left (hot, luminous stars) to the lower right (cool, dim stars). This area contains about 90% of all stars, including our Sun. Stars on the main sequence are in a stable phase of hydrogen fusion in their cores. Other regions of the HR diagram, such as the giant and white dwarf areas, contain significantly fewer stars.
The lower right part of the main sequence in the Hertzsprung-Russell diagram contains the stars that took the longest to reach the main sequence. These stars are low mass and cool, so they undergo a longer contraction phase before they start fusing hydrogen in their cores and settle onto the main sequence.
An HR (Hertzsprung-Russell) diagram illustrates two primary characteristics of stars: their luminosity (or absolute brightness) and their temperature (or spectral class). The diagram typically plots stellar temperature on the horizontal axis, increasing from right to left, while luminosity is shown on the vertical axis, increasing upward. This allows for the classification of stars into different groups, such as main sequence stars, giants, and white dwarfs, based on their evolutionary stages.
On the HR diagram, the coolest stars are located on the right side, specifically in the red dwarf region of the main sequence. These stars have low temperatures, typically ranging from about 2,500 to 3,500 Kelvin. Additionally, some cooler stars can be found in the red giant area, which is located above the main sequence on the right side.
Of course they are on the HR diagram. They are simply not on the main sequence.
main-sequence stars
The curve that currently contains most stars on the HR diagram is called the "main sequence". It consists of those stars that fuse hydrogen-1, converting it into helium-4.
The HR diagram contains only stars - so everywhere.
The location on the Hertzsprung-Russell (HR) diagram where most stars lie is known as the main sequence. The HR diagram is a plot of stellar luminosity against surface temperature. The main sequence is a prominent band that extends diagonally across the HR diagram from high temperature and high luminosity to low temperature and low luminosity. The majority of stars, approximately 90% of all stars, are situated along the main sequence on the HR diagram. These stars are often referred to as main-sequence stars. They exhibit a smooth relationship between surface temperature and luminosity, with varying sizes and masses but sharing this common characteristic of lying on the diagonal band from the upper left to the lower right of the HR diagram. Source: Teach Astronomy - The Hertzsprung-Russell Diagram
The colors of the HR Diagram are:BlueBlue-WhiteYellowOrangeRed-OrangeRed
As the HR diagram shows, the hottest stars on the main sequence range from 30,000K as blue-white stars to about 3,000K as redish stars.
In the HR-diagram, a diagram of color vs. luminosity, most stars are concentrated close to one curve, called the "main sequence". It turns out that stars on the main sequence are the stars that mainly get their energy by converting hydrogen into helium.
The majority of stars in a Hertzsprung-Russell (HR) diagram are located along the main sequence, which runs diagonally from the upper left (hot, luminous stars) to the lower right (cool, dim stars). This area contains about 90% of all stars, including our Sun. Stars on the main sequence are in a stable phase of hydrogen fusion in their cores. Other regions of the HR diagram, such as the giant and white dwarf areas, contain significantly fewer stars.
The main reason that the HR Diagram is so useful and important to scientists is, you can tell the size of the star by plotting it on the HR Diagram. The different sizes of stars form a pattern on the HR diagram.
Several regions of the HR diagram have been given names, although stars can occupy any portion. The brightest stars are called supergiants. Star clusters are rich in stars just off the main sequence called red giants. Main sequence stars are called dwarfs.
The lower right part of the main sequence in the Hertzsprung-Russell diagram contains the stars that took the longest to reach the main sequence. These stars are low mass and cool, so they undergo a longer contraction phase before they start fusing hydrogen in their cores and settle onto the main sequence.