Starship Asterisk*

[float=right][youtube]https://www.youtube.com/watch?v=zIcC8YJrevQ[/youtube][/float]
[img3="Fairy of the Eagle Nebula"]https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Fairy_of_Eagle_Nebula.jpg/320px-Fairy_of_Eagle_Nebula.jpg[/img3]

[quote=bystander post_id=294357 time=1565447036 user_id=112005]
[quote=Ann post_id=294350 time=1565416695 user_id=129702]
Mapped color images of nebulas are extremely popular today, but I prefer true color (RGB) images.
[/quote]
There really is no "true color", even RGB are mapped. You have a range of wavelengths collected through broadband filters which are then mapped to single colors, red, green, and blue, according to wavelengths passed by the filters. These images are then combined, usually with the intensities adjusted, to make a single RGB image. Closer to "true color" than narrowband images with "mapped color", but probably not what you would see on film.
[/quote]

Film, of course, is no more "true" than digital images collected through filters. And this is all further complicated by the fact that color is a physiological concept, not a physical one. The light from ionized hydrogen (Ha) isn't a single color, it is hundreds or thousands of colors, because our perception of color depends not just upon wavelength, but on intensity. We see dim Ha and bright Ha emissions as completely different colors.

[quote=ignacio_db post_id=294356 time=1565445416 user_id=133123]
Hi,

Being the author of today's image, let me chip in. I love true color astro images, even more so (in general) than false color ones. That being said, one can make a strong case for Hubble palette images. From a purely technical point of few, these images tend to reveal more subtle and fine structures than their RGB counterpart (better local contrast). They tend to be sharper, and to produce smaller stars, making structures and nebulosity to gain presence. (Note that Adam's image is taken with a 24" scope from a mountain top, while today's APOD was taken with a 6.5" scope from sea level.) Also, and most important to me, they cut through LP very effectively, allowing for deep imaging even from heavily light polluted locations (in this case, a suburban area 15 miles from downtown Buenos Aires with a population of 14 million).
From an aesthetic point of view, I personally can find beauty in both forms of representation.

Ignacio
[/quote]

Thank you for telling us this!

Ann

[quote=Ann post_id=294350 time=1565416695 user_id=129702]
Mapped color images of nebulas are extremely popular today, but I prefer true color (RGB) images.
[/quote]
There really is no "true color", even RGB are mapped. You have a range of wavelengths collected through broadband filters which are then mapped to single colors, red, green, and blue, according to wavelengths passed by the filters. These images are then combined, usually with the intensities adjusted, to make a single RGB image. Closer to "true color" than narrowband images with "mapped color", but probably not what you would see on film.

Hi,

Being the author of today's image, let me chip in. I love true color astro images, even more so (in general) than false color ones. That being said, one can make a strong case for Hubble palette images. From a purely technical point of few, these images tend to reveal more subtle and fine structures than their RGB counterpart (better local contrast). They tend to be sharper, and to produce smaller stars, making structures and nebulosity to gain presence. (Note that Adam's image is taken with a 24" scope from a mountain top, while today's APOD was taken with a 6.5" scope from sea level.) Also, and most important to me, they cut through LP very effectively, allowing for deep imaging even from heavily light polluted locations (in this case, a suburban area 15 miles from downtown Buenos Aires with a population of 14 million).
From an aesthetic point of view, I personally can find beauty in both forms of representation.

Ignacio

I really like today's version of M16; just beautiful! 8-)

I really like [url=http://www.atacama-photographic-observatory.com/page_photo.php?id=74]this widefield image[/url] by the Atacama Photographic Observatory.

I find both to be eye pleasing... the RGB has a more 3D depth to me, and the "Fairy" has a more solid look.

Thanks Ann, also for the "Ghost of Jupiter" Nebula as well.

In the Hubble pallet image the dusty areas remind me of Octopus Ink in water...

My CLOSEUP of the Pillars...lower resolution DSI 2 color camera...10" Meade LX200 scope...

:---[===] *

Thank you for providing all that extra info Ann, and for the alternate “true color” image. Even though red is my favorite color however, I have to admit that the Hubble palette image is the more attractive of the two. I’d expect the vast majority would prefer it as well. The red image is just too red, with no variety of colors that human vision craves.

Both images have great value though in the information they reveal. Thanks again for sharing some of that added info Ann.

Bruce

[float=left][img2]https://apod.nasa.gov/apod/image/1908/M16_HSHO_crop2_1024.jpg[/img2][c][size=85]M16 in mapped (Hubble palette) color.
Photo: Ignacio Diaz Bobillo.[/size][/c][/float] [float=right][img2]https://apod.nasa.gov/apod/image/1406/m16_32block950.jpg[/img2][c][size=85]M16 in "true" (RGB) color.
Photo: Adam Block.[/size][/c][/float]






















The picture at left is today's APOD, which shows M16 in mapped color. Blue color means ionized oxygen (OIII), green color means ionized hydrogen (Hα), and red means either ionized sulphur (SII) or ionized nitrogen (NII). You would be forgiven for thinking, after looking at the Hubble palette image, that M16 is completely dominated by oxygen emission. But you would be wrong.

The Adam Block picture at right is a "true color image", where red means hydrogen alpha. Provided you know that hydrogen alpha is a deep red color, you would certainly assume that M16 is completely dominated by hydrogen emission. And you would be right.


[float=left][img2]http://www.caelumobservatory.com/mlsc/n3242s.jpg[/img2][c][size=85]The Ghost of Jupiter Nebula, NGC 3242, in true color.
Photo: Adam Block.[/size][/c][/float]


There really are objects in space that are strongly dominated by blue-green OIII emission, such as planetary nebula NGC 3242. But giant star forming region M16 is not dominated by OIII at all.

The reason why you might want to use the Hubble palette for nebula images is that otherwise you can't tell the difference between Hα and SII emission. To the eye they are exactly the same color, but they represent quite different levels of ionization. The Hubble palette can tell them apart, but RGB photography cannot.

Mapped color images of nebulas are extremely popular today, but I prefer true color (RGB) images.

Ann

[url=https://apod.nasa.gov/apod/ap190810.html] [img]https://apod.nasa.gov/apod/calendar/S_190810.jpg[/img] [size=150]M16 Close Up[/size][/url]

[b] Explanation: [/b] A star cluster around 2 million years young surrounded by natal clouds of dust and glowing gas, [url=http://messier.seds.org/m/m016.html]M16 is also[/url] known as The Eagle Nebula. [url=http://www.pampaskies.com/gallery3/Hubble-Palette-Images/M16_HSHO_crop2]This beautifully detailed image[/url] of the region adopts the colorful Hubble palette and includes [url=http://en.wikipedia.org/wiki/Eagle_Nebula]cosmic sculptures[/url] made famous in Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or [url=https://apod.nasa.gov/apod/ap150107.html]Pillars of Creation[/url], dense, dusty columns rising near the center are light-years in length but are gravitationally contracting [url=http://archive.ncsa.uiuc.edu/Cyberia/Bima/StarForm.html]to form stars[/url]. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the ridge of bright emission left of center is another dusty starforming column known as the [url=http://heritage.stsci.edu/2005/12b/index.html]Fairy of Eagle Nebula[/url]. M16 lies about 7,000 light-years away, an easy target for binoculars or small telescopes in a [url=https://apod.nasa.gov/apod/ap130712.html]nebula rich[/url] part of the sky toward the split constellation [url=http://en.wikipedia.org/wiki/Serpens]Serpens Cauda[/url] (the tail of the snake).


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