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Cath

Quite a nice Hertzsprung-Russell diagram

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It is, isn't it :-)

Have saved that one, thanks for posting!

Stu

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Very nice!

certainly a little different in presentaion to the usual illustrations you see.

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I like the pointing out of visible stars. I really must get/make myself a spectrometer.... when I've got nothing else to do.. so may be 2031.. if nothing takes too long.

Derek

Edited by rfdesigner
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Derek,

The good news is you can start spectroscopy right away using a Star Analyser grating and your existing equipment.

That would give you practise while you build your DIY slit spectroscope - can be achieved with basic hand tools and a bit of care and attention - a weekend's work!

(See "Astronomical Spectroscopy for Amateurs", Section 3 for details of a Classical and a Littrow construction)

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<i>That would give you practise while you build your DIY slit spectroscope - can be achieved with basic hand tools and a bit of care and attention - a weekend's work!</i>

I have so much on my to-do list I need to start indexing it!

That's what an old house + 1/2 acre + 3 young children (one special needs) + work with commute does for you!

Derek

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Derek,

Sounds like you have a pretty full life!

Cath,

Can you advise where this HR diagram came from? I'd like to acknowledge it.

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Cath,

Thanks for that.

I can't get it to open for me.....but I'll keep trying.

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I've never seen solar radii or lifetime plotted on the HR diagram before. Really nice. What a phenomenal success it was to plot colour against absolute magnitude. One of those cases where you take all that you know, organize it in the right way, and derive lots of things you didn't know from the result. I imagine Hubble hoped that the tuning fork would be similarly productive though so far it hasn't been so.

Thanks for the post, Cath.

Olly

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A probably ignorant question for which I apologise....

Why the separation between giants and supergiants? Do these two branches meet up at some point or do these two parts behave differently?

http://www.eso.org/public/outreach/eduoff/cas/cas2002/cas-projects/uk_aldebaran_1/

This implies that Aldebaran becomes a supergiant....

Thanks

Stu

Edited by BigMakStutov

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A probably ignorant question for which I apologise....

Why the separation between giants and supergiants? Do these two branches meet up at some point or do these two parts behave differently?

http://www.eso.org/p...uk_aldebaran_1/

This implies that Aldebaran becomes a supergiant....

Thanks

Stu

I'm not an astrophysicist but look at where they leave the main sequence. The supergiants leave the MS having been very high mass, high temperature main sequence stars. The giants depart the main sequence a little below that.

Proper astrophysicist needed!

Olly

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Yes, understood they come from different roots but they do seem to head towards the same direction. If Aldebaran ends as a supergiant, is this a different sort of supergiant to the other branch of the diagram. I suppose I'm wondering what defines the clear break between these two branches, how do we know nothing crosses it?

As Olly says, astrophysicist input required :-)

Stu

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I have no idea either, but I just presume they go pop from where they are now at some point. Super nova for super giants and white dwarfs for giants - just guessing though.

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The answers can be found in James Kaler's "Stars and their spectra", 2nd Ed, Chapter 14 "Journeys on the HR diagram"

"The single most improtant factor is the star's iniial mass"

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I suppose I'm wondering what defines the clear break between these two branches, how do we know nothing crosses it?

I think it's because supergiants are massive enough to fuse helium in the core, leading to a jump in energy production.

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Why the separation between giants and supergiants? Do these two branches meet up at some point or do these two parts behave differently?

Don't quote me on this, it's late and this is just off the top of my head but....hasn't it got something to do with the Chandrasekhar Limit which is more or less equal to 1.4 solar masses?

Whether stars follow the Carbon Cycle (bigger than 1.4 solar masses) or the Proton-Proton Chain (less than 1.4 solar masses) they all, for the sake of argument, effectively convert 4 protons (Hydrogen) into 1 Alpha particle (Helium) and along the way release positrons, neutrinos, other atoms, radiation like gamma rays and great amounts of energy.

When all that hydrogen is all used up I thought stars below the Chandrasekhar Limit became red giants, then planetary nebulae, leaving behind whiite dwarfs which cool into a black dwarfs. Stars over the Chandrasekhar Limit become super red giants, supernovae, nebula and neutron or pulsar stars and that stars over 7 Chandrasekhar Limit (more than 10x solar masses) become super red giants, supernovae, nebula and black holes.

I'm not sure if the numbers are right, but I think it goes something like that.

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Shows a lot of useful stuff. Was well aware that RED supergiants are huge, but tend to forget

(for some reason) that many BLUE stars of that ilk are pretty big as well - Rigel, Deneb etc.

Certainly very uncomfortable for anyone on an earth-like orbit going around one... :p

Edited by Macavity

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I always think the temperature should go the other way - just seems wrong going from hot to colder! Still - no ones going to change it now.

As to giants, they are just small stars puffed up. As they get to the end of their life, they start burning hydrogen in shells, as all the H in the middle is basically used up and replaced by He. This is why they swell up much bigger, and get cooler - but more luminous as they are much larger. After that they may if big enough go into Helium burning - but that takes sufficient mass as it needs much hotter temperatures.

Supergiants are already huge, and burn fuel very fast, so quickly exhaust their H, but as they as soe big they can go on to burn He, C, O, Mg, Ne and so on.

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I always think the temperature should go the other way - just seems wrong going from hot to colder! Still - no ones going to change it now.

Yes but that would be just down to preference wouldn't it? .. just like how we like to write our words from left to right. Some languages around the world write from right to left across the page, or from top to bottom.

But yes it might seem better the other way round, but then it also seems OK as is Julian.

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Well - there is a lower bound to temperature 0K, but no upper limit. So I always want it to go the other way - and occasionally there are plots like that. However as its a log plot, I guess you have to pick min/max anyway.

Luminosity goes up the Y axis from dim to bright, I just think temperature should too!

In it's alternate form it's colour blue to red, and I suppose that's less clear cut.

Anyway - as I said - its not going to change now, just like other silly systems such as magnitude, OBAFGKM, and "early-type" galaxies - we're stuck with them!

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Yes I agree.

We have our sink/bath taps marked wrong, red should be cold, blue should be hot, just like stars. But then varoius substances/metals start glowing red when they get hot, then white when very hot. We can't win lol.

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post-20192-0-51877000-1372481359_thumb.j

Oh heck, it makes me feel positively sea sick!

I've often wondered, though, why it is plotted as it is. Did HNR and EH both decide on the temperature going from hotter to colder,and, if so, why?

Olly

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