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Author Topic: Stars in a telescope?  (Read 2155 times)

Offline RayG

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Stars in a telescope?
« on: 14/11/2014 19:40:39 »
If we can get fantastic detailed pictures from objects 7500 light years away (like the "Pillars of Creation"), why can't we get good detailed images of a nearby star such as Proxima Centauri that's only 4.5 LY away? Using proper filters as we do when photographing our own sun, why aren't we oohing and ahhhing over the sunspot activity on other stars?

I THINK there have been attempts at Betelgeuse, but resolution seems to be shaky at best.


 

Offline PmbPhy

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Re: Stars in a telescope?
« Reply #1 on: 14/11/2014 22:40:39 »
Quote from: RayG
If we can get fantastic detailed pictures from objects 7500 light years away (like the "Pillars of Creation"), why can't we get good detailed images of a nearby star such as Proxima Centauri that's only 4.5 LY away?
Dear Ray,

Welcome to the forum! :)

Why can't we get such details from stars as we do the Pillars of Creation? For the obvious reason, i.e. stars are way too far away to get any detail whatsoever. Due to the extremely large distance from the earth to a start, all stars look like a point of light. The disks of most stars are much too small in angular size to be observed with current ground-based optical telescopes.

Let's consider the example you gave, i.e. the Pillars of Creation. See http://en.wikipedia.org/wiki/Pillars_of_Creation

Let's compare this to a giant star whose radius is about 250 times the radius of our Sun making the radius of a typical giant star about 150x106 km. However such stars are light years away where a light year is 1 trillion km, i.e. 1011 km. Proxima Centauri is about 40x1011 km.

Now compare this with the Pillars of Creation. The leftmost pillar is about four light years in length. The finger-like protrusions at the top of the clouds are larger than our solar system. Therefore the Pillars of Creation are significantly larger than even the largest of stars and are enormous in size so that we can see a great deal of detail in them.

I hope that helped! :)
 

Offline RayG

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Re: Stars in a telescope?
« Reply #2 on: 15/11/2014 03:48:30 »
Fair enough... But am I correct in thinking/remembering that we have tried to image Betelgeuse? I remember seeing an article with something about variations in the color or atmosphere...
 

Offline PmbPhy

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Re: Stars in a telescope?
« Reply #3 on: 15/11/2014 05:10:41 »
Quote from: RayG
Fair enough... But am I correct in thinking/remembering that we have tried to image Betelgeuse? I remember seeing an article with something about variations in the color or atmosphere...
Sorry. I'm unfamiliar with it. I'm not an astrophysicist anyway.
 

Offline evan_au

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Re: Stars in a telescope?
« Reply #4 on: 15/11/2014 20:54:22 »
Quote
variations in the color of [a star's] atmosphere
There are a number of stars which expand and contract over time, with significant changes in brightness and color.
Cepheid Variable stars do this in a regular pattern; Betelguese does it irregularly.
But this is mostly studied by looking at the brightness of the star, or its spectrum, not by taking an image of the surface.

Quote
am I correct in thinking/remembering that we have tried to image Betelgeuse?
There is a technique known as speckle interferometry that can give grainy images of a star's disk.
Examples of Betelgeuse, Capella and Vega are shown in section E. Betelguese is particularly large, bright, and relatively close, which makes this easier. The main benefit of this work was to come up with an estimate of the star's diameter, to confirm theories about the interior of stars, rather than to take photos of the star's surface (not easy in the case of Betelguese, because its diameter keeps changing...).

This technique is currently more useful when studying the separation of close binary stars, which requires far less resolution.

Recently, the ALMA telescope obtained some high resolution images of the disk of dust surrounding a star, with gaps that presumably contain planets. But it is a long way from obtaining surface images of a star (other than the Sun).

The highest resolution images we can obtain at present are not at visible wavelengths, but at microwave wavelengths. It is possible to link radio telescopes across the diameter of the Earth, using Very Long Baseline Interferometry.

To get good images of the surface of a star would require many large optical telescopes, spaced out over a distance of several km, with a high-capacity optical network to accurately combine the images. This is beyond our current technical and funding capabilities.
 

Offline RD

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Re: Stars in a telescope?
« Reply #5 on: 15/11/2014 21:01:33 »
... Recently, the ALMA telescope obtained some high resolution images of the disk of dust surrounding a star, with gaps that presumably contain planets ...


http://www.thenakedscientists.com/forum/index.php?topic=26311.msg443799
« Last Edit: 15/11/2014 21:04:13 by RD »
 

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Re: Stars in a telescope?
« Reply #5 on: 15/11/2014 21:01:33 »

 

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