APOD: The Great Globular Cluster in Hercules (2024 Sep 26)

[Chris Peterson]

No? Why was this star "discovered" and found to be very remarkably blue compared to the other members of M13 as early as in the year 1900?

Ann

Because they didn't have panchromatic film. It was no more striking photographically then than it is today. It would be discovered no less readily today.

Chris, you know what has been said about the bumblebee? It can't fly, and yet it does.

A bumblebee at flight. Credit: Bumblebee Conservation Trust

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You seem to be saying that the astronomers of the very early 1900s couldn't have detected the UV peculiarity of Barnard 29. And yet they did.

Or perhaps you are just saying that it is a miracle that they did detect it more than a hundred years ago, because it did not stand out in any way back then?

Ann

???
I'm not saying any of those things! Only that it was no less obvious to them then than it is to us now.

[Ann]

Because they didn't have panchromatic film. It was no more striking photographically then than it is today. It would be discovered no less readily today.

Chris, you know what has been said about the bumblebee? It can't fly, and yet it does.

A bumblebee at flight. Credit: Bumblebee Conservation Trust

---

You seem to be saying that the astronomers of the very early 1900s couldn't have detected the UV peculiarity of Barnard 29. And yet they did.

Or perhaps you are just saying that it is a miracle that they did detect it more than a hundred years ago, because it did not stand out in any way back then?

Ann

???
I'm not saying any of those things! Only that it was no less obvious to them then than it is to us now.

I shouldn't be telling you what you are saying or implying, you are right about that. I apologize.

Still, I insist that Barnard 29 would have stood out more to the early 20th century astronomers than it typically does to us. Take a look at the pictures that AVAO, jac, posted:

Click to view full size image 1 or image 2

XMM-Newton-UV and SDSS9-opt jac berne (flickr)


As you can see, Barnard 29 looks much brighter in UV light than it does in an RGB image. Because of its UV brightness alone, and because it is located away from the most crowded center of M13, it is very likely that it would have caught the eye of of some astronomers back then. And spectroscopy was already available, so some astronomers, probably Barnard himself, may have analyzed this star's spectrum and noticed that it was very hot, much hotter than most other stars in M13.

Secchi's four classes of stellar spectra, from a colored lithograph in a book published around 1870. This shows how someone looking through a spectrograph on a large telescope would see the spectrum from the brightest stars. Copyright is uncertain.

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So I still say that Barnard 29 stood out more a hundred years ago in the astronomical photography of the time than it does now.

Ann

[Chris Peterson]

Chris, you know what has been said about the bumblebee? It can't fly, and yet it does.

A bumblebee at flight. Credit: Bumblebee Conservation Trust

---

You seem to be saying that the astronomers of the very early 1900s couldn't have detected the UV peculiarity of Barnard 29. And yet they did.

Or perhaps you are just saying that it is a miracle that they did detect it more than a hundred years ago, because it did not stand out in any way back then?

Ann

???
I'm not saying any of those things! Only that it was no less obvious to them then than it is to us now.

I shouldn't be telling you what you are saying or implying, you are right about that. I apologize.

Still, I insist that Barnard 29 would have stood out more to the early 20th century astronomers than it typically does to us. Take a look at the pictures that AVAO, jac, posted:

Click to view full size image 1 or image 2

XMM-Newton-UV and SDSS9-opt jac berne (flickr)


As you can see, Barnard 29 looks much brighter in UV light than it does in an RGB image. Because of its UV brightness alone, and because it is located away from the most crowded center of M13, it is very likely that it would have caught the eye of of some astronomers back then. And spectroscopy was already available, so some astronomers, probably Barnard himself, may have analyzed this star's spectrum and noticed that it was very hot, much hotter than most other stars in M13.

Secchi's four classes of stellar spectra, from a colored lithograph in a book published around 1870. This shows how someone looking through a spectrograph on a large telescope would see the spectrum from the brightest stars. Copyright is uncertain.

---

So I still say that Barnard 29 stood out more a hundred years ago in the astronomical photography of the time than it does now.

Ann

I still disagree, because you're comparing apples to oranges. Nobody would take a survey image today with a broadband sensor. They'd use several filters, and one of those would closely match the response of the film used 100 years ago. So the star would be just as obvious to an astronomer today as it was then.

[AVAO]

Chris, you know what has been said about the bumblebee? It can't fly, and yet it does.

A bumblebee at flight. Credit: Bumblebee Conservation Trust

---

You seem to be saying that the astronomers of the very early 1900s couldn't have detected the UV peculiarity of Barnard 29. And yet they did.

Or perhaps you are just saying that it is a miracle that they did detect it more than a hundred years ago, because it did not stand out in any way back then?

Ann

???
I'm not saying any of those things! Only that it was no less obvious to them then than it is to us now.

I shouldn't be telling you what you are saying or implying, you are right about that. I apologize.

Still, I insist that Barnard 29 would have stood out more to the early 20th century astronomers than it typically does to us. Take a look at the pictures that AVAO, jac, posted:

Click to view full size image 1 or image 2

XMM-Newton-UV and SDSS9-opt jac berne (flickr)


As you can see, Barnard 29 looks much brighter in UV light than it does in an RGB image. Because of its UV brightness alone, and because it is located away from the most crowded center of M13, it is very likely that it would have caught the eye of of some astronomers back then. And spectroscopy was already available, so some astronomers, probably Barnard himself, may have analyzed this star's spectrum and noticed that it was very hot, much hotter than most other stars in M13.

Secchi's four classes of stellar spectra, from a colored lithograph in a book published around 1870. This shows how someone looking through a spectrograph on a large telescope would see the spectrum from the brightest stars. Copyright is uncertain.

---

So I still say that Barnard 29 stood out more a hundred years ago in the astronomical photography of the time than it does now.

Ann

Barnard used yellow-tinted glass plates as filters for his investigations. He was able to determine the color differences from the difference to images taken without a yellow filter. This was probably the first time in 1909 that color differentiations in stars in globular clusters could be scientifically identified and analyzed precisely.

[Ann]

Barnard used yellow-tinted glass plates as filters for his investigations. He was able to determine the color differences from the difference to images taken without a yellow filter. This was probably the first time in 1909 that color differentiations in stars in globular clusters could be scientifically identified and analyzed precisely.

Thanks! So that does explain why Barnard would be able to actually "see" that Barnard 29 was so blue and bright!

Also, and this is my gut feeling, I think that astronomers back in the day of Barnard and earlier would have been extra interested in blue and ultraviolet objects, because these were the objects they could photograph easily with their blue-sensitive film. I mean, take a look at this early Harvard photograph of the Southern Cross again. Which of the stars look more more interesting to you? Blue Alpha and Beta Crucis at right, or red Gamma Crucis at top right?

Old Harvard picture of Crux, the Southern Cross, taken on blue-sensitive film. The two bright stars at right are hot blue stars beta and alpha Crucis. The bright star at upper left is hot star epsilon Centauri. Note however that cool red M-type star gamma Crucis, seen at upper right at top of the Crux asterism, is almost invisible. The photograph is from circa 1925.

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Ann

[AVAO]

Barnard used yellow-tinted glass plates as filters for his investigations. He was able to determine the color differences from the difference to images taken without a yellow filter. This was probably the first time in 1909 that color differentiations in stars in globular clusters could be scientifically identified and analyzed precisely.

Thanks! So that does explain why Barnard would be able to actually "see" that Barnard 29 was so blue and bright!

Also, and this is my gut feeling, I think that astronomers back in the day of Barnard and earlier would have been extra interested in blue and ultraviolet objects, because these were the objects they could photograph easily with their blue-sensitive film. I mean, take a look at this early Harvard photograph of the Southern Cross again. Which of the stars look more more interesting to you? Blue Alpha and Beta Crucis at right, or red Gamma Crucis at top right?

Old Harvard picture of Crux, the Southern Cross, taken on blue-sensitive film. The two bright stars at right are hot blue stars beta and alpha Crucis. The bright star at upper left is hot star epsilon Centauri. Note however that cool red M-type star gamma Crucis, seen at upper right at top of the Crux asterism, is almost invisible. The photograph is from circa 1925.

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Ann

ThanX Ann Wonderful comparisons, as always!

I think, however, that after Chris's vote we need to differentiate between filter methods and the use of color-sensitive films, which didn't exist at the time. But the idea of ​​working with yellow filters to increase the contrast of blue stars against the the very bright sea of ​​other stars of M13 was pretty ingenious for the time.

Jac