Starship Asterisk*

Ann wrote: ↑Thu Dec 14, 2023 12:21 am

Chris Peterson wrote: ↑Wed Dec 13, 2023 7:32 pm

Ann wrote: ↑Wed Dec 13, 2023 6:55 pm

But RGB imagery, when done carefully, does show us when OIII emission is bright and when it isn't.

Ann

Or just hides it from us.

Well, Chris, consider the Orion Nebula. I found a great LRGB picture of the Orion Nebula by Ian Howarth:


Orion Nebula in LRGB Ian Howarth.png


Note the grayish, ever so slightly greenish color of the Trapezium region in Ian Howarth's image. The color is due to a combination of some red Hα, a lot of green OIII and some blue starlight being scattered in the area.

You will be hard pressed to find any pictures of the Orion Nebula where the Trapezium region looks "all red". In most pictures it will look white, and in a few it will look yellow, as from a combination of red Hα and green OIII. And there are several closeups of the Trapezium region where the background looks green or blue.

So it seems clear to me that the OIII emission is a lot brighter in the Trapezium region than in the Heart Nebula. It is bright enough to very clearly affect the visual appearance of the Trapezium region. Of course, an important difference between the Trapezium region and the inner Heart Nebula is that the Trapezium region is so much smaller, so that the OIII emission is very concentrated there.

Even so, the difference is striking.

Ann

Chris Peterson wrote: ↑Wed Dec 13, 2023 7:32 pm

Ann wrote: ↑Wed Dec 13, 2023 6:55 pm

Chris Peterson wrote: ↑Wed Dec 13, 2023 6:19 pm

This, of course, is why RGB imagery isn't very good for most emission nebulas. And why narrowband is very much the way to go, as it actually shows us what elements are present in a way that RGB seldom can.

But RGB imagery, when done carefully, does show us when OIII emission is bright and when it isn't.

Ann

Or just hides it from us.

Ann wrote: ↑Wed Dec 13, 2023 6:55 pm

Chris Peterson wrote: ↑Wed Dec 13, 2023 6:19 pm

Ann wrote: ↑Wed Dec 13, 2023 6:11 pm

The Heart Nebula isn't bright in oxygen. If it were, its inner region would be very clearly turquoise in RGB images.

Planetary nebula IC 1295 is very bright in oxygen. Therefore its color is bright turquoise.

IC 1295. Credit: Adam Block.

---

Note the colorful background stars. We have very good reasons to believe that Adam Block portrait of IC 1295 is an RGB image.

But look at what the Heart Nebula looks like an an RGB image:

Heart Nebula IC 1805 Amy Astro.png

Heart Nebula in RGB. Credit: Amy Astro.

There is no sign of green or blue nebulosity in the inner parts of the Heart Nebula in Amy Astro's image. But yes, you can tease out a bit of blue from inside the Heart Nebula if you try hard:

Heart Nebula Bob Franke.png

Heart Nebula. Credit: Bob Franke

.

If you go to this page, you can see that the longest of Bob Franke's exposures for his portrait of the Heart Nebula (apart from the luminosity filter) was through the blue filter.

My point is that that there is indeed OIII in the inner regions of the Heart Nebula, but this OIII emission isn't very bright at all. But you are right, Chris, that this part of IC 1805 has been mostly cleared of hydrogen.

Ann

This, of course, is why RGB imagery isn't very good for most emission nebulas. And why narrowband is very much the way to go, as it actually shows us what elements are present in a way that RGB seldom can.

But RGB imagery, when done carefully, does show us when OIII emission is bright and when it isn't.

Ann

Chris Peterson wrote: ↑Wed Dec 13, 2023 6:19 pm

Ann wrote: ↑Wed Dec 13, 2023 6:11 pm

Chris Peterson wrote: ↑Wed Dec 13, 2023 2:49 pm

The nebula includes that surrounding gas and dust. I'd say the nebula is primarily dust and hydrogen, with a central region that appears to have been cleared of much of the hydrogen revealing oxygen.

The Heart Nebula isn't bright in oxygen. If it were, its inner region would be very clearly turquoise in RGB images.

Planetary nebula IC 1295 is very bright in oxygen. Therefore its color is bright turquoise.

IC 1295. Credit: Adam Block.

---

Note the colorful background stars. We have very good reasons to believe that Adam Block portrait of IC 1295 is an RGB image.

But look at what the Heart Nebula looks like an an RGB image:

Heart Nebula IC 1805 Amy Astro.png

Heart Nebula in RGB. Credit: Amy Astro.

There is no sign of green or blue nebulosity in the inner parts of the Heart Nebula in Amy Astro's image. But yes, you can tease out a bit of blue from inside the Heart Nebula if you try hard:

Heart Nebula Bob Franke.png

Heart Nebula. Credit: Bob Franke

.

If you go to this page, you can see that the longest of Bob Franke's exposures for his portrait of the Heart Nebula (apart from the luminosity filter) was through the blue filter.

My point is that that there is indeed OIII in the inner regions of the Heart Nebula, but this OIII emission isn't very bright at all. But you are right, Chris, that this part of IC 1805 has been mostly cleared of hydrogen.

Ann

This, of course, is why RGB imagery isn't very good for most emission nebulas. And why narrowband is very much the way to go, as it actually shows us what elements are present in a way that RGB seldom can.

Ann wrote: ↑Wed Dec 13, 2023 6:11 pm

Chris Peterson wrote: ↑Wed Dec 13, 2023 2:49 pm

johnnydeep wrote: ↑Wed Dec 13, 2023 2:19 pm So, it seems to me that the Heart Nebula is really just a heart-shaped less dense region in the surrounding denser gas and dust. No?

The nebula includes that surrounding gas and dust. I'd say the nebula is primarily dust and hydrogen, with a central region that appears to have been cleared of much of the hydrogen revealing oxygen.

The Heart Nebula isn't bright in oxygen. If it were, its inner region would be very clearly turquoise in RGB images.

Planetary nebula IC 1295 is very bright in oxygen. Therefore its color is bright turquoise.

IC 1295. Credit: Adam Block.

---

Note the colorful background stars. We have very good reasons to believe that Adam Block portrait of IC 1295 is an RGB image.

But look at what the Heart Nebula looks like an an RGB image:

Heart Nebula IC 1805 Amy Astro.png

Heart Nebula in RGB. Credit: Amy Astro.

There is no sign of green or blue nebulosity in the inner parts of the Heart Nebula in Amy Astro's image. But yes, you can tease out a bit of blue from inside the Heart Nebula if you try hard:

Heart Nebula Bob Franke.png

Heart Nebula. Credit: Bob Franke

.

If you go to this page, you can see that the longest of Bob Franke's exposures for his portrait of the Heart Nebula (apart from the luminosity filter) was through the blue filter.

My point is that that there is indeed OIII in the inner regions of the Heart Nebula, but this OIII emission isn't very bright at all. But you are right, Chris, that this part of IC 1805 has been mostly cleared of hydrogen.

Ann

Chris Peterson wrote: ↑Wed Dec 13, 2023 2:49 pm

johnnydeep wrote: ↑Wed Dec 13, 2023 2:19 pm So, it seems to me that the Heart Nebula is really just a heart-shaped less dense region in the surrounding denser gas and dust. No?

The nebula includes that surrounding gas and dust. I'd say the nebula is primarily dust and hydrogen, with a central region that appears to have been cleared of much of the hydrogen revealing oxygen.

Chris Peterson wrote: ↑Wed Dec 13, 2023 2:49 pm

johnnydeep wrote: ↑Wed Dec 13, 2023 2:19 pm So, it seems to me that the Heart Nebula is really just a heart-shaped less dense region in the surrounding denser gas and dust. No?

The nebula includes that surrounding gas and dust. I'd say the nebula is primarily dust and hydrogen, with a central region that appears to have been cleared of much of the hydrogen revealing oxygen.

johnnydeep wrote: ↑Wed Dec 13, 2023 2:19 pm So, it seems to me that the Heart Nebula is really just a heart-shaped less dense region in the surrounding denser gas and dust. No?