Red star question

[N3ptune]

Hello I am trying to understand something on color temperature of stars.

If I look at various tables with O B A F G K M basic informations, they say a "M" star is Red <3500 kelvins, for example, Betelgeuse is M2Ib

But when I look at Betelgeuse in my telescope or even with unaided eye, the star appears Orange, not red. I never saw any red star except for the planet Mars which looks like a true red  star with unaided eye.

Is there a simple explanation for that, which a 10 years old could understand? (I am the 10 years old)

[rockystar]

I think this to do with astronomers categorising stars based on their temperature - So colder stars appear towards the red (orange is near red on the colour spectrum) - rather than how it appears to each person.

if you want find a truely red star, see if you can find Hind's crimson star .

[jsmoraes]

stars are emission body, not reflection body, and star has emission in all spectrum of visible and not visible light. Your eyes will do a combination of them. So what you see isn't what they are.
The atmosphere cause some interference on this apparent color, also.

the link https://docs.kde.org/trunk5/en/kdeedu/kstars/ai-colorandtemp.html  will explain better why we classify a star as red or blue or ...

And why we don't see green stars ?

Take a look at:

1) http://blogs.discovermagazine.com/badastronomy/2008/07/29/why-are-there-no-green-stars/#.VwAfX7uANLN

2)  http://blogs.discovermagazine.com/badastronomy/2008/08/28/followup-green-objects-in-space/#.VwAgK7uANLN

 

By the same reasons we can say that the Sun isn't yellow, it is blue-peach. (if we take his temperature as reference: 5778 Kelvin)

http://www.science20.com/solar_fun_of_the_heliochromologist/blog/the_color_of_the_sun

http://www.science20.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_part_ii

 

[ronin]

A "cool" red star still emits light up in the orange and green band of the visual spectrum. Additionally if you think about it you do not "see" yellow, the eye sees Red and Green and if the body it is coming from has about equal amounts then it is interpretted as yellow. All interpretation.

I would guess that a red star has the peak of the transmitted wavelengths at a wavelength considered red, what that wavelength is I do not know, likely there are several, or a defined band. However as that is only the peak then the additional wavelengths also emitted have to be considered for when the eye is involved. A star that emits with a peak at the green wavelengths is not green it is yellow - our sun being the obvious example.

I have a 650nm filter that to me looks Orange, but 650nm is usually considered red.

The term Red will just be a catch all description as in red stars, yellow stars, white stars, blue stars. After that you need a spectral analysis for greater detail.

Be interesting to find out what colour you consider Antares to be when it appears.

If you want red stars then I think you will need to consider the carbon stars.

[jsmoraes]

In short words. See the white  intensity curve. Your eyes will sum the blue, green and red colors informations. The intensity of these informations will result more red or less red (orange).

 

[N3ptune]

rockystar
if you want find a truely red star, see if you can find Hind's crimson star .

--> Thanks I am looking forward to see that Hind's crimson star. (quite faint it's going to be a challenge to find it maybe)

jsmoraes

--> thanks for the links, ill try to read a little, my caseload of reading is quite big right now but I am reading. hehehe

Ronin
Be interesting to find out what colour you consider Antares to be when it appears.

--> I definitely want to look at Antares (: I never watched this star yet, great suggestion.

If you want red stars then I think you will need to consider the carbon stars.

--> The Hind's crimson star. (:

===========
Conclusion

The main reason I don't see Betelgeuse has a true red star but orange could be one or multiple of the following things:

-Stars will do a combination of spectrums so what i see isn't what they are.
-Atmosphere cause interference on apparent color.
-Orange is part of the red band of the visual spectrum so orange is red in a sens. At what temperature in kelvin can we say red stops? 5000 K ? (maybe it's irrelevant to Betelgeuse because of point #1 and #2 but just for fun)
-The term Red will just be a catch all description as in red stars, yellow stars, white stars, blue stars.
Your eyes will sum the blue, green and red colors informations. The intensity of these informations will result more red or less red (orange).

 

[Davey-T]

If you get up early you can compare Mars and Antares, due South about 5.00am.

Dave

[Dave In Vermont]

Our atmosphere plays a large role in showing us stars in colour. If you were in outer-space, the stars would all appear to be white. Some brighter, some dimmer.

Dave

[N3ptune]

35 minutes ago, Dave In Vermont said:

Our atmosphere plays a large role in showing us stars in colour. If you were in outer-space, the stars would all appear to be white. Some brighter, some dimmer.

Dave

Not so simple after all..

- The books say Betelgeuse is red

- In space Betelgeuse is white

- On earth Betelgeuse it's orange.

(((: Kind of funny but its complicated science really.

 

[Dave In Vermont]

I wouldn't say it's complicated, but requires an acquired knowledge of prism's and their cousins' the spectroscopes as an overview of refraction & diffraction. From there one is at the mercy of a good teacher taking the time and trouble to explain such entities in ways you can understand. The hardest part of this, and other sciences, is finding a 'good teacher.' A good science-teacher can often be a highly elusive prey. I had one utter bozo who failed me in chemistry - saying I lacked the aptitude to learn such. I had a private tutor at home who was helping me with advanced organic chemistry! This fool was in a town school who was teaching (or trying to - sort of) beginning-chemistry and had no clue I was busy doing advanced university chemistry!

My parent's, tutor, and I had a long laugh at this twit. I quit the school. My tutor is now the Minister of Science in Tanzania!

As for stars like the brightly coloured Betelgeuse, think of the Earth's atmosphere as being like a prism. It takes other things like heat, not just light, into account to produce the colour we see. As well as the angle of view - which changes and contributes to the finished result that we see at present. And this tosses a variable into the equation. As do our personal colour-sense. Some people see red as orange and the reverse.

Not too complicated?

Dave

Hind's Crimson Star -  R Leporis

[jsmoraes]

Quote

 

The main reason I don't see Betelgeuse has a true red star but orange could be one or multiple of the following things:

Stars will do a combination of spectrums so what i see isn't what they are.

 

No, who do combination is your eyes and brain. Star is source of radiation in many spectrum, visible and not visible. The temperature determine what spectrum will be more strong.

Quote

Atmosphere cause interference on apparent color.

Yes, it filter more the high fequency (small wavelength) as blue.

Quote

Orange is part of the red band of the visual spectrum so orange is red in a sens.

No, orange is a combination done by your eyes and brain. We haven't sensor for this spectrum in our eyes.

We are quite blind. We see a very small range of wavelength (frequency). We have only sensor to red, green and blue. And more sensitivity to green. Because this, the color cameras have more pixels to green: two times.

It is important you perceive that some objects reflect the light. They don't emit that light. They haven't temperature to irradiate that light: a kind of energy.

Others don't reflect, they radiate the light. In this case they will emit many wavelengths. One will be the most strong. Its temperature determine which of them will be stronger.

The color that we see is a kind of "corruption" done by our eyes and brain.

The importance of star colors is because you can know how much fuel it has. Or what years old it is. Stars with predominance of red emission are old stars, dying. It had burned its most fuel.

Blue stars are new stars. Or it is in the primary stage of life, with great amount of  primary sequence of termo-nuclear reaction: hydrogen to helium.

A good text (and easy) about the life of a star.

http://staff.on.br/jlkm/astron2e/AT_MEDIA/CH21/CHAP21AT.HTM

Sequence of the star termo-nuclear reaction:

Hydrogen to helium to Lithium to Carbon to Silicon to Iron to ... explosion of the star.

All others chemical elements are done in Nova and Supernova. Star doesn't burn Iron as fuel. It can not do it !

[N3ptune]

Dave, with teachers you always get one with whom you have a personality conflict and the following results... Has for my studies I read slowly, and re read previous things to memorize, I am definitely not meant to go to school and study in maths or science. But you had the chance to study with a great teacher that's a great feeling I can understand that, once I studied Aikido with a great teacher and his techniques were fabulous, those are rare opportunities.  Did you quit the science studies now ?

The picture of the crimson star is beautiful, the contrast between the other blue star to the left, fantastic. thanks for sharing that.

==========

Has for the orange/red star conclusion, jsmoraes thanks for these explanations, I re read your last message many times to do a correlation between my quote about the red band and what you said, it's not understood 100% but I have a better idea right now regarding various factors influencing what I see and why it's orange instead of something else.

This was useful.

So ill resume by saying this. Betelgeuse is a red star but my brain and eyes (because of their limitations and many other factors) process the star color has orange.

[Dave In Vermont]

Quit my science-studies? Persish the thought! After I did the best thing I've ever done for myself - by walking out of the schools in my town - my mother was in hysterics. But my father took the news stoically. He was a tenured professor at MIT. The next day when he came home from MIT, he handed me an MIT Affiliate's Card. This entitled me to walk into any university, college, etc. - and use their resources, libraries, audit courses, talk with professor's and students, and so forth. These are good-for-life. I was 12 years old.

Being autodidactic, I designed my own course of studies and, for all intents & purposes, moved into MIT and Harvard  (they're both in Cambridge, Massachusetts) and went to work in the vastness of their libraries (and many others over the years). Learning as much science as I could get my hands on, learning the technical forms of most every European languages to translate science papers from all over, studying political-sciences, history, and everything else I could think of. Meanwhile, the school department I walked out on had written me off as retarded and disturbed!

And this was just for the first couple of months.

At the age of 15 I was in a very advanced private school for advanced kids who were also primarily autodidactic. Excellent teacher, no "Mr. This and Miss That." First names all around. And as I was by now doing graduate-school level organic-chemistry, I was given a key to the school and began teaching chemistry there. My first official foray into education. The idiot school-department in my home-town, believing I was hopelessly "retarded" (their word, not mine), they had to pay my tuition to what they presumed was a "special school" for poor, brainless morons - like me!

I hope you find this enlightening. In case you know of other young folks facing such a situation. This is meant to manifest what it's possible to do with a good nudge!  

I never stopped my education project,

Dave

 

[ollypenrice]

We shouldn't forget carbon stars which really are red!

I liked jsmoraes' post with the two stars and their blackbody curves. This offers the OP a clear explanation. While a star may peak in the red, and so be called a red star, it's perceived colour is affected by the colours either side of the peak.

Olly

[MAN or ASTROMAN]

Mu Cepheii is an easily found carbon star,not as red as R Leporis,but a lot easier to find,and at a higher altitude.

[michaelmorris]

There is a really good article on colour perception and stars here

http://www.handprint.com/ASTRO/bineye4.html

What is surprising is that differences in star colours is often pretty subtle.  However, the eye/brain system tends to exaggerate these differences.