# Talk:Hertzsprung–Russell diagram

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• Fix the references at the bottom of the page

## Untitled

The text mentions "red giants" which doesn't appear as a label in the diagram. Just to avoid confusion, either the text or diagram should be changed (by someone who knows what they are doing). GreatWhiteNortherner 12:23, Jan 10, 2004 (UTC)

Hi User:Looxix! I have some questions about the diagram. Can you add some informations about the meaning of the numbers on both axis? What is the source of the data points? The statistical distribution on the sheet lets me assume, that this are manually and arbitrary distributed points and not actually existing stars. Is that correct? Is there anybody who knows how to get real data for instance from the Hipparcos satellite? I'm from the german WP, where this diagram is used as well. --Wolfgangbeyer 21:45, 8 Apr 2004 (UTC)

Someone should include where our Sun is on this diagram :) Indosauros 14:00, Jul 14, 2004 (UTC)

## Mathematical Relationship?

The first sentence: "... Hertzsprung-Russell diagram shows the mathematical relationship between absolute magnitude, luminosity,..." is nonsense. There is no mathematical relationship between these quantities. As a matter of fact, the H-R-diagram doesn's show something like a perfect graph of a function, but a cloud of points. Therefore the diagram "only" shows physical relationships. --CWitte 10:05, 28 Jan 2005 (UTC)

I have changed the lead so that it now specifies that HRD's are scatter graphs. --RoyGoldsmith (talk) 14:00, 2 August 2009 (UTC)

So is it true that Annie Cannon and other women astronomers discovered this relationship and had the credit taken by Hertzsprung and Russel? (comment from anon 08:06, 2005 Feb 3)

On a first random check on the internet, it seems he made his diagram about five years earlier (1905 ) than she was working on the topic (1911->1914, same source) and that it's quite correct to credit the diagram to (independently both of) Hertzsprung and Russell, whilst the detailed classification based on it is being correctly attributed to Annie Cannon (again same source). Do you have any more deatail about this? In what way did they take her credit? Mozzerati 08:44, 2005 May 8 (UTC)

## Great A'Tuin

I removed the following link on the grounds of utter irrelevancy. Gene Ward Smith 06:28, 10 October 2005 (UTC)

## Distance

```Could someone tell me how distance is calculated from the diagram.
Thank you! (Unsigned comment from User:JML)
```
I'm not experienced in the field, but I'd guess that since the colour and apparent magnitude are known, one can assume that the absolute magnitude is on the main sequence, and use the ratio of apparent to absolute magnitude to determine the distance. --Stoive 18:40, 23 September 2006 (UTC)

## Names?

Could someone please add a chart of star names by size, instead of lumping them all into "supergiants" and "medium stars?" I mean all of the blue giant, red giant, red dwarf, etc.

## Not a colour magnitude diagram

I am a professional astronomer and I always thought that a HR diagram and a colour magnitude plot were different things. Where a HR diagram uses Absolute magnitude (via knowledge of the distance) a colour mag diagram uses apparent magnitude (Where no distance is known). Though I am not sure if HR also pioneered this as well, I would say that its reference to colour is an indication that it was a plot that could be drawn from photometry alone, and hence useful to astronomers.Soloist 18:18, 18 October 2006 (UTC)

I am not a professional, but I am currently a student, and my understanding was the same. However, googling color magnitude diagram returns a number of examples of people in astronomy using color magnitude diagram and Hertzsprung Rusell diagram interchangeably. Of course, there were also examples of people using color magnitude diagram to refer to a plot using apparent magnitude. I think I'll just add a note to that effect in the article. James McBride 19:06, 18 July 2007 (UTC)

I am also a professional astronomer, working on stars. A colour-magnitude diagram (CMD) that uses apparent magnitudes is useful for a group of stars that are all at (about) the same distance, such as a cluster or an external galaxy. In the days before good parallaxes were available for large numbers of stars, these were the most common. Since Hipparcos, we can make CMDs using absolute magnitudes for many tens of thousands of stars. Both of these are often called HR diagrams, although I think CMD is better. A plot of luminosity versus effective temperature, such as evolutionary tracks produced from theoretical models, is (I think) more properly called a theoretical HR diagram. I have not checked, but I would be confident that the original diagrams by H and R themselves would have been apparent-magnitude CMDs using V and B photometry of clusters. Timb66 23:59, 18 July 2007 (UTC)

## Color Accuracy

One of the quirks in astronomy has been the lingering view that the Sun is a yellow star. Actually, it appears yellow only when there is enough atmospheric extinctions of the shorter wavelengths (i.e. at sunset or sunrise). Without atmospheric effects, the Sun, with proper attenuation, will appear only white, even along the limb. I think most H-R diagrams will show the Sun as being a yellow star. Often the Sun is plotted in the yellow portion of thie main sequence illustration. This very nice H-R diagram would be improved if the white portion shown extended much closer to a B-V value near +0.8, into the K-class somewhere.

Here is a blog that demonstrates why the Sun is clearly not a yellow star. http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_revelation

The hotter "blue" stars of the H-R color diagram are very nicely done. Not until temperatures reach into the millions of degrees will the blue end be strong enough to be the dominant color seen. The very hot O-class stars simply have too much radiation throughout their entire visible spectrum to produce an appearance more blue than bluish-white. Thus, the cyan color drawn seems appropriate. The Heliochromologist (talk) 20:50, 27 July 2010 (UTC)

## Bet you find this Interesting?

I had a thought the other day. And tried to find this answer to this on Wikipedia and other sources. But as a complete layman became very confused, parsecs/light years ect. This is my thought, we (the human race) have been sending out RF signals of a reasonable strength since 1922, please correct me on this if I have this wrong. Based on this knowledge, I wondered how far and how many star like suns (G class stars) have these RF signals reached by this year, 2007 ? You know where I'm going with this thought, and yes maybe life is not restricted to G class stars, or maybe it is, or maybe only to G2V, and we all known G2V's are capable! Then there's the age of these stars, and then the metallic make up as well. I wish someone with the right knowledge would draw up a list of theses stars. And using the above knowledge. We could then break the list up into the most lightly to the most unlikely places that intelligent life may exist. And that have also received RF signals from us. I believe this list would be helpful to SETI, to reduce their listing down to size, so they can focus on a more broader range of RF signals. As I also believe the RF's they are searching are far too narrow, and I feel a lot of time and money is going to waist at SETI. If anyone can help me with this please do, maybe I've got this wrong as I'm just a layman. But in any case, post me something, its bugging me! —The preceding unsigned comment was added by 86.10.204.128 (talk) 23:52, 20 March 2007 (UTC).

SETI already does that (targets G-class, middle-aged, stable stars), and they always have. (Answered for the sake of people looking on this page casually) 128.230.72.232 (talk) 00:39, 17 October 2011 (UTC)

## Image too big

Image:Hertzsprung-Russell diagram Richard Powell.png is too big. It cannot be used in shrinked dimensions because of blur. It won't be practical to replace it with an SVG. Hence it should be regenerated in a smaller size. How? Said: Rursus 20:12, 30 April 2007 (UTC)

## Confusion about interpretation of diagram

One thing I have never understood is exactly what the logic is that gets astronomers from the observed set of points on the H-R diagram to the knowledge that the diagram represents an evolutionary sequence. How do we know that the main sequence is the longest lifetime of stars, or that the section in the upper right is giant stars?

--Raddick 18:03, 25 July 2007 (UTC)

Theorists end up doing lots of modelling and simulation trying to predict what should happen, yet the bounds of uncertainty are still quite large. Key concepts include metallicity and other clues about absolute age of stars, like rotation rate, variability, absolute magnitude but the logic is still quite intricate; and I think that process needs adequate explanation in the article. -- 99.233.186.4 (talk) 05:15, 25 February 2010 (UTC)
This interview with Allan Sandage gives a good deal of background to the thinking about the relationship between the HR diagram and stellar evolution.[1] Thincat (talk) 11:26, 26 February 2010 (UTC)

## Original Publication

I found an article on nasa ads "Relations Between the Spectra and Other Characteristics of the Stars" by russell which seems to be the first publication describing the Herzsprung-Russell relation. If so it should be mentioned or referenced somewhere; otherwise the first publication should be found and mentioned.

see: http://adsabs.harvard.edu/abs/1914PA.....22..331R Zoltan 06:09, 24 December 2008 (UTC) —Preceding unsigned comment added by Lzkelley (talkcontribs)

I am almost certain that Hertzsprung's first version of a diagram came before Russell's ... the two came on the idea independently ... but I will need to do some library work to find the hard reference. BSVulturis (talk) 17:36, 14 April 2010 (UTC)

## Biology and theology

When reading the paragraph "Hertzsprung–Russell diagram#The diagram's role in the development of stellar physics" I noticed that there is some confusion between the debate over the age of the sun (Kelvin-Darwin in the 1860's) and the understanding about the track a star makes during it's lifetime. I also read somewhere (notes from the 30 year celebration to the HR or something like that) there was a time where it was believed a star begins it's life as an O star and as it loses mass to energy it becomes lighter transforming to an M star. It was assumed this process takes much longer than the current prediction to the age of the sun. Amirber (talk) 08:32, 18 September 2010 (UTC)

## Solar color index in caption

All references I can find are that the solar index is closest to 0.656, not 0.96. —Preceding unsigned comment added by 68.126.200.155 (talk) 07:40, 7 December 2010 (UTC)

Yes, you are right. I have undone a (deliberate) error introduced a few days ago. Well spotted! Thincat (talk) 21:00, 7 December 2010 (UTC)

## Theoretical HRD

I think we should include the theoretical HRD on this page. Something like http://en.wikipedia.org/wiki/File:Stellar_evolutionary_tracks-en.svg which shows the evolutionary tracks along with stages of evolution marked on the track. I'm working with them in my research and I was surprised to find evolutionary tracks missing from this page. Durand101 (talk) 16:00, 14 February 2012 (UTC)

## Vertical axis mislabeled in the two open clusters' HRD figure

I feel sheepish for noticing this only now (I have used the figure multiple times, for several years, and I really like it) but the vertical axis of the M67/NGC188 HRD figure, http://en.wikipedia.org/wiki/File:Open_cluster_HR_diagram_ages.gif ,is mislabeled: larger absolute magnitudes go toward the bottom of the graph, so the arrow should point down, not up, in that graph. The originator of the image has retired from Wikipedia, so it's unlikely we can prevail upon him to fix it. Can someone generate a corrected version? BSVulturis (talk) 01:59, 16 August 2013 (UTC)