How is our sun classified on the h r diagram

We have met the white dwarfs already, in a theoretical way. Now let's see where the real ones come from. The Sun is classified as a G2 star. Red Giants And White Dwarfs Red giants and white dwarfs come about because stars, like people, change with age and eventually die. For people, the cause of aging is the deterioration of biological functions.

For a star, the cause is the inevitable energy crisis as it begins to run out of nuclear fuel. Since its birth 4. This causes the nuclear reactions to run a little hotter. The Sun brightens. This brightening process moves along very slowly at first, when there is still ample hydrogen remaining to be burnt at the center of the star. But eventually, the core becomes so severely depleted of fuel that its energy production starts to fall regardless of the increasing density.

When this happens, the density of the core begins to increase even more, because without a heat source to help it resist gravity, the only possible way the core can respond is by contracting until its internal pressure is high enough to hold up the weight of the entire star. Bizarrely, this emptying of the central fuel tank makes the star brighter, not dimmer, because the intense pressure at the surface of the core causes the hydrogen there to burn even faster.

This more than takes up the slack from the fuel-exhausted center. The star's brightening not only continues, it accelerates. We do not know exactly, but in two words or less, the answer is: greenhouse effect. The Earth's atmosphere evidently had a much higher greenhouse gas content four billion years ago, which kept it warm. In fact, very warm. Various complex bio-geological feedback loops have steadily decreased the greenhouse effect precisely because the Sun is getting brighter.

The Sun is about half-way through a very long process of shifting from a mode where hydrogen is burned in a kernel at its center to a mode where hydrogen will be burned in a spherical shell wrapped around an intensely hot, very dense, but quite inert, helium core. Once it makes the transition from core burning to shell burning, it will be entering its twilight years.

Stars in group B are mostly 6, K or cooler yet more luminous than main sequence stars of the same temperature. How can this be? The reason is that these stars are much larger than main sequence stars. These stars are referred to as giants.

Examples include Aldebaran and Mira. The stars in group C are even more luminous than the giants. These are the supergiants , the largest of stars with extremely high luminosities. A red supergiant such as Betelgeuse would extend beyond the orbit of Jupiter if it replaced the Sun in our solar system. The final group of interest are those stars in group D. From their position on the H-R diagram we see that they are very hot yet very dim. Although they emit large amounts of energy per square metre they have low luminosity which implies that they must therefore be very small.

Group D stars are in fact known as white dwarfs. Sirius B and Procyon B are examples. White dwarfs are much smaller than main sequence stars and are roughly the size of Earth.

The diagram below shows the main groups labelled together with example stars in each group. In outward appearance, he was an old-fashioned product of the nineteenth century who wore high-top black shoes and high starched collars, and carried an umbrella every day of his life. His papers were enormously influential in many areas of astronomy. Born in , the son of a Presbyterian minister, Russell showed early promise. When he was 12, his family sent him to live with an aunt in Princeton so he could attend a top preparatory school.

He lived in the same house in that town until his death in interrupted only by a brief stay in Europe for graduate work. He was fond of recounting that both his mother and his maternal grandmother had won prizes in mathematics, and that he probably inherited his talents in that field from their side of the family. Before Russell, American astronomers devoted themselves mainly to surveying the stars and making impressive catalogs of their properties, especially their spectra as described in Analyzing Starlight.

Russell began to see that interpreting the spectra of stars required a much more sophisticated understanding of the physics of the atom, a subject that was being developed by European physicists in the s and s.

Russell embarked on a lifelong quest to ascertain the physical conditions inside stars from the clues in their spectra; his work inspired, and was continued by, a generation of astronomers, many trained by Russell and his collaborators.

Russell also made important contributions in the study of binary stars and the measurement of star masses, the origin of the solar system, the atmospheres of planets, and the measurement of distances in astronomy, among other fields. He was an influential teacher and popularizer of astronomy, writing a column on astronomical topics for Scientific American magazine for more than 40 years.

He and two colleagues wrote a textbook for college astronomy classes that helped train astronomers and astronomy enthusiasts over several decades.

That book set the scene for the kind of textbook you are now reading, which not only lays out the facts of astronomy but also explains how they fit together. Russell gave lectures around the country, often emphasizing the importance of understanding modern physics in order to grasp what was happening in astronomy. Today, one of the highest recognitions that an astronomer can receive is an award from the American Astronomical Society called the Russell Prize, set up in his memory.

Figure 3. Along the horizontal axis, we can plot either temperature or spectral type also sometimes called spectral class. Several of the brightest stars are identified by name. Most stars fall on the main sequence. Following Hertzsprung and Russell, let us plot the temperature or spectral class of a selected group of nearby stars against their luminosity and see what we find Figure 3. Such a plot is frequently called the Hertzsprung—Russell diagram , abbreviated H—R diagram.

It is one of the most important and widely used diagrams in astronomy, with applications that extend far beyond the purposes for which it was originally developed more than a century ago. It is customary to plot H—R diagrams in such a way that temperature increases toward the left and luminosity toward the top.

Notice the similarity to our plot of height and weight for people Figure 1. Stars, like people, are not distributed over the diagram at random, as they would be if they exhibited all combinations of luminosity and temperature. Instead, we see that the stars cluster into certain parts of the H—R diagram. The great majority are aligned along a narrow sequence running from the upper left hot, highly luminous to the lower right cool, less luminous.

This band of points is called the main sequence. It represents a relationship between temperature and luminosity that is followed by most stars. We can summarize this relationship by saying that hotter stars are more luminous than cooler ones. A number of stars, however, lie above the main sequence on the H—R diagram, in the upper-right region, where stars have low temperature and high luminosity.

How can a star be at once cool, meaning each square meter on the star does not put out all that much energy, and yet very luminous? The only way is for the star to be enormous—to have so many square meters on its surface that the total energy output is still large. These stars must be giants or supergiants , the stars of huge diameter we discussed earlier.

Figure 4. Schematic H—R Diagram for Many Stars: Ninety percent of all stars on such a diagram fall along a narrow band called the main sequence. A minority of stars are found in the upper right; they are both cool and hence red and bright, and must be giants.

Some stars fall in the lower left of the diagram; they are both hot and dim, and must be white dwarfs. There are also some stars in the lower-left corner of the diagram, which have high temperature and low luminosity. If they have high surface temperatures, each square meter on that star puts out a lot of energy.

How then can the overall star be dim? It must be that it has a very small total surface area; such stars are known as white dwarfs white because, at these high temperatures, the colors of the electromagnetic radiation that they emit blend together to make them look bluish-white. We now know that stars are mostly hydrogen and helium and differ only slightly in chemical makeup. Later it was discovered that the temperature was the main reason why the spectral lines differed so greatly from one star to another.

Rather than change the letters which had already been assigned to the stars, they just decided to understand the meaning of the letters differently. The letters become excellent temperature indicators. This also means astronomers have another way of determining the temperature of a star, - Wien's Law and spectral lines. Each letter is subdivided using a number from hot to cool , so a B3 star is slightly hotter than a B4 star.

Our sun's photosphere is about K 11, F. On this scale, it is classified G2. We showed before that these stars appear bright to us because they are for the most part extremely luminous look at their absolute magnitudes. If you recall, the luminosity of a star is a function of the radius and temperature. Look at Rigel absolute magnitude of This star is luminous because it is both hot B8 and big super giant - I.

If you look at Betelgeuse you will see a cool star M2 that gives off a lot of light It does this by having a large radius. If you were to place Betelgeuse in our solar system, it would extend beyond the orbit of Mars and there are stars even bigger than this.