APOD: M78 from the Euclid Space Telescope (2024 May 24)

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APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by APOD Robot » Fri May 24, 2024 4:08 am

Image M78 from the Euclid Space Telescope

Explanation: Star formation can be messy. To help find out just how messy, ESA's new Sun-orbiting Euclid telescope recently captured the most detailed image ever of the bright star forming region M78. Near the image center, M78 lies at a distance of only about 1,300 light-years away and has a main glowing core that spans about 5 light-years. The featured image was taken in both visible and infrared light. The purple tint in M78's center is caused by dark dust preferentially reflecting the blue light of hot, young stars. Complex dust lanes and filaments can be traced through this gorgeous and revealing skyscape. On the upper left is associated star forming region NGC 2071, while a third region of star formation is visible on the lower right. These nebulas are all part of the vast Orion Molecular Cloud Complex which can be found with even a small telescope just north of Orion's belt.

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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by Ann » Fri May 24, 2024 5:54 am

APOD Robot wrote:
ESA's new Sun-orbiting Euclid telescope recently captured the most detailed image ever of the bright star forming region M78.
Really? Is that because this is a combined optical and infrared image?

The purple tint in M78's center is caused by dark dust preferentially reflecting the blue light of hot, young stars.

I protest! Blue star light does not make purple reflection nebulas! 🤬

Consider the van den Bergh catalog of reflection nebulas. You can find it here. I challenge you to find a single purple reflection nebula in this catalog.

Or why not google "M78 nebula" and "pictures"? You'll get a ton of M78 images. Most of them make M78 look blue, some of them make it look almost colorless, and ESO infrared image makes it look pink, and some amateur images make the entire area, reflection nebula, dust lanes, background and all look purple. Not a single other image produces a color distribution similar to today's APOD.

The purple color of M78 in today's APOD was caused by the artistic choices of the people processing the image. The filters chosen for image may also have something to do with the palette of the final product.

So what kind of M78 images do I prefer? Well, there was an M78 APOD from January 21, 2021 which is nice:


M78 is almost colorless in this APOD. That's okay. M78 isn't very strongly colored.

This picture by John Hayes is nice. I hope I get to keep it here:

ayMCFu0PNs3R_1824x0_vcyuAHGw[1].jpg
M78. Credit: John Hayes.

Ann
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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by JimB » Fri May 24, 2024 8:25 am

Ann wrote: Fri May 24, 2024 5:54 am Blue star light does not make purple reflection nebulas! 🤬
Ann
The info on the ESA site says
The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue.
So I suspect that the purple colour is a result of the blue being combined with the red they have used for the infra-red band.

PS: Look at all those little galaxies lurking in the background detail when you zoom in.
Really gives a sense of the unimaginable vastness of space!

Peter Smith

Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by Peter Smith » Fri May 24, 2024 8:34 am

The brightest foreground stars show six straight diffaction spikes and also at least two arcs. Are the arcs similarly an artefact of the way the telescope's mirror is mounted?

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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by Ann » Fri May 24, 2024 9:04 am

JimB wrote: Fri May 24, 2024 8:25 am
Ann wrote: Fri May 24, 2024 5:54 am Blue star light does not make purple reflection nebulas! 🤬
Ann
The info on the ESA site says
The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue.
So I suspect that the purple colour is a result of the blue being combined with the red they have used for the infra-red band.

PS: Look at all those little galaxies lurking in the background detail when you zoom in.
Really gives a sense of the unimaginable vastness of space!
Thanks, Jim!

Infrared images don't show the same color palette as pictures taken with filters sensitive to visible wavelengths of light.

That explains it! Thanks! :D

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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by johnnydeep » Fri May 24, 2024 1:12 pm

Peter Smith wrote: Fri May 24, 2024 8:34 am The brightest foreground stars show six straight diffaction spikes and also at least two arcs. Are the arcs similarly an artefact of the way the telescope's mirror is mounted?
You beat me to asking about the arcs. Clearly it's an optical artifact, but what causes it and why is it only visible on some stars? I don't know, but I'm sure someone here will!

m78 from euclid telescope.jpg
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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by Christian G. » Fri May 24, 2024 2:32 pm

Euclid images have a soft dreamy feel!
Euclid.jpg
M78_Euclid_960.jpg
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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by AVAO » Fri May 24, 2024 8:05 pm

Ann wrote: Fri May 24, 2024 5:54 am
[...]
The purple color of M78 in today's APOD was caused by the artistic choices of the people processing the image. The filters chosen for image may also have something to do with the palette of the final product.
[...]

Ann

... In principle, the Euclid color palette can be transferred very easily ...

Here's the comparison with Hubble. Cool wide angle & macro combo ;-)

Click to view full size image 1 or image 2
Click to view full size image 1 or image 2
jac berne (flickr)
HH24 / original data: NASA / ESA
Last edited by AVAO on Sat May 25, 2024 5:34 am, edited 3 times in total.

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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by Ann » Sat May 25, 2024 4:13 am

AVAO wrote: Fri May 24, 2024 8:05 pm
Ann wrote: Fri May 24, 2024 5:54 am
[...]
The purple color of M78 in today's APOD was caused by the artistic choices of the people processing the image. The filters chosen for image may also have something to do with the palette of the final product.
[...]

Ann

... In principle, the Euclid color palette can be transferred very easily ...

Here's the comparison with Hubble. Cool wide angle & macro combo ;-)

Click to view full size image 1 or image 2
Click to view full size image 1 or image 2
Click to view full size image 1 or image 2
jac berne (flickr)
HH24 / original data: NASA / ESA

Thanks a bunch, Jac, but the blue hue you showed me is too "harsh and saturated" to really appeal to me! I don't believe that "that kind of blue" exists in stars or nebulas. One of the bluest things that can be found on the Earth - and in the Universe? - is natural lapis lazuli, which is, however, typically mixed with other minerals and is not the same shade of blue everywhere.


What are my favorite pictures, colorwise, of M78? Well, here's a real confetti color bomb:


I like the color bomb picture and it makes me smile, but I can't take it really, really seriously.


My favorite portrait of M78 (of those I could easily find by googling) is still the one by John Hayes.


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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by VictorBorun » Sun May 26, 2024 6:12 am

JimB wrote: Fri May 24, 2024 8:25 am
Ann wrote: Fri May 24, 2024 5:54 am Blue star light does not make purple reflection nebulas! 🤬
Ann
The info on the ESA site says
The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue.
So I suspect that the purple colour is a result of the blue being combined with the red they have used for the infra-red band.

PS: Look at all those little galaxies lurking in the background detail when you zoom in.
Really gives a sense of the unimaginable vastness of space!
Suppose a faraway galaxy has its green photons (.515 μm in sRGB or 0.532 μm in HDTV) redshifted to the green channel of the presentations of Euclid's filters (1.1 μm, that would mean space expansion 2.1 times during the photons' travel).
Then the blue would represent 0.7 μm /2.1 = 0.33 μm photons, a UV just a little short of violet, and the red would represent 1.7 μm /2.1 = 0,81 μm photons, an IR just a little long of crimson.
Therefore such a galaxy would be rendered slightly more colourful than in life, as if it was photoshopped to more saturated colours.

According to Ned Wright's Javascript Cosmology Calculator with the default settings, a galaxy with the redshift of z=2.1 is seen as it was at the age 3.161 Gyr since the Big Bang. Such a galaxy should be young and its core should not be red-and-dead; not at all like orange core / blue arms grand design of a galaxy 13 Gyr old.

Another thing Ned's Calculator tells us is the angular distance, 5.7 Gly, which is 5.7 Gly / 206 kly = 28000 times the distance to Small Magellanic Cloud. SMC angular size is 5°20′ × 3°5′, and a similar galaxy at 28000 times the angular distance should have an angular size of 0.69'' × 0.40'' (these '' means arc seconds here). Now Euclid resolves 0.3'' in IR and therefore such a galaxy would look like a pair of pixels.

(By the way, there is a redshift of the maximum angular distance. According to that calculator with the default settings, it's z=1.6 and the angular distance is 5.8 Gly, and a galaxy the size of SMC would be pretty the same pair of pixels, just little bluer and brighter than at z=2.1. At redshifts z>1.6 the more distant is a galaxy the less is its angular distance. The angular distance stays the same as the space expands; it is the distance as it was at the time when the galaxy emitted the photons we can see now. The most early galaxies that JWST can see, as they were 0.4 Gyr since the Big Bang, are heavily redshifted with z=11.5 and dimmed 11.5 times by photons' count, too, but enjoy a healthy angular size, their angular distance being just 2.6 Gly).

Well, let's hunt a little.
Euclid’s_new_image_of_star-forming_region_Messier_78 -2.jpg
Euclid’s_new_image_of_star-forming_region_Messier_78 -1.jpg
Does it look like real colours of galaxies? Or are the disks too red and the cores too orange?
IMHO those galaxies are redshifted heavier than z=2.1 and Euclid's representation (RGB channels for 1.7, 1.1, and 0.7 μm) does not quite compensate such a redshift.

And I still wonder why should early (3 Gyr or younger) disk galaxies be redder at their rims than at their cores.
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Re: APOD: M78 from the Euclid Space Telescope (2024 May 24)

Post by VictorBorun » Tue May 28, 2024 10:52 am

VictorBorun wrote: Sun May 26, 2024 6:12 am
JimB wrote: Fri May 24, 2024 8:25 am
Ann wrote: Fri May 24, 2024 5:54 am Blue star light does not make purple reflection nebulas! 🤬
Ann
The info on the ESA site says
The blue, green, red channels capture the Universe seen by Euclid around the wavelength 0.7, 1.1, and 1.7 micron respectively. This gives Euclid a distinctive colour palette: hot stars have a white-blue hue, excited hydrogen gas appears in the blue channel, and regions rich in dust and molecular gas have a clear red hue.
So I suspect that the purple colour is a result of the blue being combined with the red they have used for the infra-red band.

PS: Look at all those little galaxies lurking in the background detail when you zoom in.
Really gives a sense of the unimaginable vastness of space!
Update: Calculations edited to correct my misinterpretation of z; λ_registered/λ_emitted does not equal z; it is rather z+1.

Suppose a faraway galaxy has its green photons (.515 μm in sRGB or 0.532 μm in HDTV) redshifted to the green channel of the presentations of Euclid's filters (1.1 μm, that would mean space expansion 2.1 times during the photons' travel).
Then the blue would represent 0.7 μm /2.1 = 0.33 μm photons, a UV just a little short of violet, and the red would represent 1.7 μm /2.1 = 0,81 μm photons, an IR just a little long of crimson.
Therefore such a galaxy would be rendered slightly more colourful than in life, as if it was photoshopped to more saturated colours.

According to Ned Wright's Javascript Cosmology Calculator with the default settings, a galaxy with the redshift of z=1.1 is seen as it was at the age 5.519 Gyr since the Big Bang. Such a galaxy should be young and its core should not be red-and-dead; not at all like orange core / blue arms grand design of a galaxy 13 Gyr old.

Another thing Ned's Calculator tells us is the angular distance, 5.58 Gly, which is 5.58 Gly / 206 kly = 27,000 times the distance to Small Magellanic Cloud. SMC angular size is 5°20′ × 3°5′, and a similar galaxy at 27,000 times the angular distance should have an angular size of 0.71'' × 0.41'' (these '' means arc seconds here). Now Euclid resolves 0.3'' in IR and therefore such a galaxy would look like a pair of pixels.

(By the way, there is a redshift of the maximum angular distance. According to that calculator with the default settings, it's z=1.6 and the angular distance is 5.8 Gly, and a galaxy the size of SMC would be pretty the same pair of pixels, just little bluer and brighter than at z=1.1. At redshifts z>1.6 the more distant is a galaxy the less is its angular distance. The angular distance stays the same as the space expands; it is the distance as it was at the time when the galaxy emitted the photons we can see now. The most early galaxies that JWST can see, as they were 0.4 Gyr since the Big Bang, are heavily redshifted by z+1=12.5 times and dimmed 12.5 times by photons' count, too, but enjoy a healthy angular size, their angular distance being just 2.6 Gly).

Well, let's hunt a little.

Euclid’s_new_image_of_star-forming_region_Messier_78 -2.jpgEuclid’s_new_image_of_star-forming_region_Messier_78 -1.jpg

Does it look like real colours of galaxies? Or are the disks too red and the cores too orange?
IMHO those galaxies are redshifted heavier than z+1=2.1 and Euclid's representation (RGB channels for 1.7, 1.1, and 0.7 μm) does not quite compensate such a redshift.

And I still wonder why should early (3 Gyr or younger) disk galaxies be redder at their rims than at their cores.