H-R Diagram, 1 Novermber 2013!The HR diagram of temperature vs. inherent brightness has taught scientists a 1.great deal about how the universe works, indicated several things to look for in the future, and is the unifying concept of the entire stars unit.!Inherent brightness is also called "absolute luminosity"(and "absolute a.magnitude," but we don't need to know why)!"Absolute" has an unfamiliar meaning in this context that is confusing, 1.but makes an important point:!If stars are following regular rules of behavior, some of those rules A.should deal with their inherent characteristics. !How far a star is from the Earth is an accident. !a.A star's mass, temperature, age, and composition are inherent b.characteristics. Stars that share these characteristics should behave in the same way. !If similar stars didn't behave the same way, then the HR 1.diagram wouldn't work. !Surface temperature increases to the left and luminosity increases b.upward. !If temperature increases in the conventional way, the main A.sequence curve resembles Take a Nebula, Condense and Stir: !Take a Nebula, Condense, and Stir uses core temperature a.instead of surface temperature.!This is because new advances in technique since the tim eof 1.the first HR diagram allow astronomers to tell the core temperature of stars, and that is more important than surface temperature. !Core temperature determines what's going on in an A.object, !It also uses mass instead of luminosity, because mass is more b.fundamental than luminosity. !The differences in the brightness of stars is due to how much 1.mass they start out with. !This is the only diagram that emphasizes the common ancestry c.of all the objects in the solar system: !Everything starts out at the solar nebula, and the differences 1.that arise can be plotted out on a single chart. !The HR diagram was created once astronomers had accurate star distances in 2.the 1900s.!This is because you need to know a star's distance to tell its inherent A.luminosity. !There were some precursors to the HR diagram in the 1800s, but there B.wasn't enough data to be certain. !It was Hertzsprung and Russell who made the diagram what is is today. !C.A Danish astronomer named Hertzsprung published the diagram in a.1905, but it was mostly ignored. !This is because he published it in Danish (which few astronomers 1.understood) and in the journal of the Danish Photographic Society (which few astronomers read).!The reason he published this data in a photographic journal was A.that he based it on spectra which he captured with astrophotography. !Compounding these issues, he published his data in a tedious data 2.table.!Unless a person is passionately interested in a subject, they are not A.going to read through a data table. !In 1913, Russell remedied the problems of Hertzsprung's presentation b.and promoted the idea: !He wrote the article in English, which more astronomers could read. !1.German was the international language of science, but a lot more A.astronomers could read English than could read Danish. !He replaced the data table with a graph that instantly communicated 2.the trends of the data. !This graph was an ancestor to the HR diagram!A.He promoted the idea by giving talks at many universities and major 3.meetings of astronomers in the US, Canada, and Europe. !Russell was working on these charts independently, although he did 4.see Hertzsprung's charts before he published his own and acknowledge Hertzsprung's prior work on the subject. !His data was also strongly overlapping. !A.It takes both research and skillful promotion to make an impact: !c.Even if you come up with a scientific breakthrough, you have to bring 1.attention to it for it to have any effect. !A lot of people are good at one of these things and not the other.!A.If you are in a modern institution, there are people who will a.help you make up for this.!If you are a loner, this is a problem.!b.If, like Hertzsprung, you live 100 years ago and are not a c.director– this is also a problem.! There are many graphically different versions of the HR diagram, but all of 3.them have the same basic characteristics: a main sequence in the middle, a smattering of white dwarves below, and a smattering of red giants above. !The only real difference is in the artist. !A.There are problems with the conventional way of describing certain stars on a 4.HR diagram: !You do not memorize this, but it is a good illustration of a problem that A.plagues many research fields.!There is no generally agreed upon name for white stars on the main B.sequence: !Almost all textbooks tell you that the stars on the main sequence are all a.dwarves, but this isn't so: Everything along the top of the diagram is a giant, including the blue giants in the main sequence. !Blue giants: A class with a relatively few stars because they tend to 1.have extremely short lives. The ones that formed have long since died. !Astronomers sometimes make distinctions among red giants when 2.color is important. From right to left: red giants, orange giants, yellow giants, and white giants. !Almost all astronomers will tell you there is no star in between giants 3.above the main sequence and dwarves on and below the mainsequence. !A problem arises in naming the stars directly below the blue giants on 4.the main sequence that are not hot enough to be blue giants. !They are not as short lived as blue giants. !A.They are white, but they cannot be called white dwarves, because B.that is a well established name for the white stars below the main sequence.!White main sequence star is understandable, but no one uses it. !C.Most astronomers dodge the issue by referring to the stars by their b.spectra types. !Red Dwarf stars are in a vicious cycle of obscurity: !5.Red dwarves are the most abundant star in our stellar neighborhood. !A.They are so abundant is because nature makes a lot of them and they a.have a long lifespan (longer than the universe so far). !They are faint and require a good telescope to be studied. !b.Time on these good telescopes is in high demand. !1.However, because they have a reputation for never producing any new, B.interesting results, no one studies them.!Applications for time on good telescopes to study red dwarves are a.rejected by time allocation committees in favor of topics that seem more promising. !People can sneak some time in if they are part of an institution which 1.at least partially owns a good telescope. !For example, the UC system
View Full Document
Unlocking...