Starship Asterisk*

beryllium732 wrote: ↑Thu Jun 02, 2022 9:10 am
It's a bit late but thank you! It's amazing! It would be a sight to behold if we could be there at that particular time. The light from them would be blindingly bright at least for the light we would be able to see.

So the redshift shifts the ultraviolet which we can't see with our eyes to the 400-500nm range in the visible spectrum which we can see?

Ann wrote: ↑Thu Mar 17, 2022 9:31 pm

beryllium732 wrote: ↑Thu Aug 05, 2021 12:31 am I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

The Hubble Deep Field. Image credit: NASA and the European Space Agency. Edited by Noodle snacks.

---

Take a look at this picture the Hubble Deep Field. There really are a number of small blue galaxies that are a lot more distant than many of the orange galaxies. How can the blue galaxies look blue if they are more redshifted than many of the orange ones?

This artist’s impression shows CR7, a very distant galaxy discovered using ESO’s Very Large Telescope. It is by far the brightest galaxy yet found in the early Universe and there is strong evidence that examples of the first generation of stars lurk within it. These massive, brilliant, and previously purely theoretical objects were the creators of the first heavy elements in history — the elements necessary to forge the stars around us today, the planets that orbit them, and life as we know it. This newly found galaxy is three times brighter than the brightest distant galaxy known up to now. Credit: ESO/M. Kornmesser

---

Answer: Because they are so blue and starforming in themselves. Or rather, they are extremely ultraviolet, pumping out huge amounts of far ultraviolet light from their massive, extremely hot stars. We see these galaxies as they looked at the age of peak star formation in the Universe. More importantly: The far ultraviolet light from these galaxies has been redshifted so that it looks blue.

Abell 370: Galaxy Cluster Gravitational Lens. Image Credit: NASA, ESA, Hubble; Processing & Copyright: Rogelio Bernal Andreo (DeepSkyColors.com)

---

What about the much larger yellow or orange galaxies? Many of them are elliptical galaxies, devoid of star formation. They lack hot stars altogether. Other orange galaxies do have some star formation, but not a lot of it, and they don't form very hot or massive stars.

The orange galaxies are dominated by yellow-white stars, and because these galaxies are redshifted, they look yellow or orange to us.

The green-looking galaxies aren't green. They are just redshifted galaxies that have been detected by the green filter used for the image, or else they are simply "intermediate" in color and have been mapped as green.

Ann

beryllium732 wrote: ↑Thu Aug 05, 2021 12:31 am I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Shmurk wrote: ↑Thu Mar 17, 2022 7:28 pm I found this same exact picture march 5th 2018. any reason for repeats in pics and description?

Q4: Have some APOD pictures been run more than once?
A4: Yes. Many of our readers have been with us less than a year and are unaware of some really spectacular or important astronomy pictures. New information about old pictures is becoming available over the WWW. The text and links for rerun pictures will make use of this newly available information. So although the picture might be old, some of the text and links of each APOD will be new. Also, more web surfers have larger bandwidth connections, which allows us to post higher-resolution image files that can be transferred conveniently. Software to handle more sophisticated image file formats has also become more common, so the picture's size and/or format might be new. Lastly, rerunning APODs saves us time and helps us update our archive. In general, our rerun policy currently is to only rerun APODs more than one year old to keep the pictures relatively "new" to new APOD viewers. We will almost never rerun more than two pictures in any given week. So when you load the current APOD,it is still, most probably, a new picture.

beryllium732 wrote: ↑Fri Aug 06, 2021 5:09 pm
Isn't the UDF showing the real visible spectrum?

neufer wrote: ↑Thu Aug 05, 2021 1:25 pm

beryllium732 wrote: ↑Thu Aug 05, 2021 12:31 am
I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Another example in the picture is two galaxies one more blueish the other more reddish which looks to be neightbours but the reddish one is nine billion light years away and still the one farthest away is still as big as the much nearer galaxy. Is there a lens effect in play here?

Can someone explain?

HUDF colors vs. visible Hubble colors

---

The rainbow HUDF "colors" are NOT true colors
in the narrow "octave": Violet (380 nm) to Red (740 nm)
but represent a broader (~435 to ~1600 nm) spectrum
in which broad Black Body radiation often
appear as narrow pure primary pseudo-colors:

Code: Select all

Camera 	Filter 	Wavelength 	Exposure time
----------------------------------------------
ACS 	F435W 	 435 nm 	56 orbits
ACS 	F606W 	 606 nm 	56 orbits
ACS 	F775W 	 775 nm 	144 orbits
ACS 	F850LP 	 850 nm 	144 orbits
WFC3 	F105W 	1050 nm 	14 orbits
WFC3 	F125W 	1250 nm 	16 orbits
WFC3 	F160W 	1600 nm 	28 orbits
...................................................
		Spitzer? 

beryllium732 wrote: ↑Thu Aug 05, 2021 12:31 am
I find this very fascinating but two things bothering me. Why are there more blueish galaxies that shows them much farther away for exampel billions light years more distant than more reddish galaxies? I also see plenty of green galaxies. How come they look green?

Another example in the picture is two galaxies one more blueish the other more reddish which looks to be neightbours but the reddish one is nine billion light years away and still the one farthest away is still as big as the much nearer galaxy. Is there a lens effect in play here?

Can someone explain?

Camera 	Filter 	Wavelength 	Exposure time
----------------------------------------------
ACS 	F435W 	 435 nm 	56 orbits
ACS 	F606W 	 606 nm 	56 orbits
ACS 	F775W 	 775 nm 	144 orbits
ACS 	F850LP 	 850 nm 	144 orbits
WFC3 	F105W 	1050 nm 	14 orbits
WFC3 	F125W 	1250 nm 	16 orbits
WFC3 	F160W 	1600 nm 	28 orbits
...................................................
		Spitzer? 

bystander wrote: ↑Wed Aug 04, 2021 4:18 pm

johnnydeep wrote: ↑Wed Aug 04, 2021 2:49 pm

bystander wrote: ↑Wed Aug 04, 2021 2:23 pm

Hubble Ultra Deep Field 2014

As I tried to show above, this APOD seems to show the XDF not the UDF, though the XDF is nevertheless just an 80% sub-FOV of the UDF.

This is not just the XDF. It's the XDF plus UV.

johnnydeep wrote: ↑Wed Aug 04, 2021 2:49 pm

bystander wrote: ↑Wed Aug 04, 2021 2:23 pm

JohnM wrote: ↑Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John

Hubble Ultra Deep Field 2014

As I tried to show above, this APOD seems to show the XDF not the UDF, though the XDF is nevertheless just an 80% sub-FOV of the UDF.

bystander wrote: ↑Wed Aug 04, 2021 2:23 pm

JohnM wrote: ↑Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John

Hubble Ultra Deep Field 2014

JohnM wrote: ↑Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John

JohnM wrote: ↑Wed Aug 04, 2021 11:47 am Is the image in fact the Ultra Deep Field or is it the Extreme Deep Field ?

The image looks more like the Extreme Deep Field .

I did not think the UDF had galaxies to a look back of 13.1 gyr as it did not have the Hubble far infrared data that is in the extreme deep field.

Comments ?

John

Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full moon.

The Hubble Ultra Deep Field is an image of a small area of space in the constellation Fornax, created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over many hours of observation, it revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time.

The new full-color XDF image is even more sensitive, and contains about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see.

The Hubble eXtreme Deep Field (HXDF), released on September 25, 2012, is an image of a portion of space in the center of the Hubble Ultra Deep Field image. Representing a total of two million seconds (approximately 23 days) of exposure time collected over 10 years, the image covers an area of 2.3 arcminutes by 2 arcminutes,[15] or approximately 80% of the area of the HUDF. This represents approximately one thirty-two millionth of the sky.

The HXDF contains approximately 5,500 galaxies, the oldest of which are seen as they were 13.2 billion years ago.

2stepbay wrote: ↑Mon Aug 02, 2021 8:42 pm
13.1. A mere walk in the galactic woods

"If an astronaut falls in a galactic wood, does he make a sound when no one can here him scream "

neufer wrote: ↑Mon Aug 02, 2021 2:53 pm

• z = 0.96 => F♯4 (370 Hz) => 10.6 Gly (comoving radial distance)
  z = 1089 => 0.666 Hz => Cosmic Microwave Background

Click to play embedded YouTube video.

https://en.wikipedia.org/wiki/Infrasound wrote:
. . . Air is a very inefficient medium for transferring low frequency vibration from a transducer to the human body. Mechanical connection of the vibration source to the human body, however, provides a potentially dangerous combination. The U.S. space program, worried about the harmful effects of rocket flight on astronauts, ordered vibration tests that used cockpit seats mounted on vibration tables to transfer "brown note" and other frequencies directly to the human subjects. . . .

MarkBour wrote: ↑Mon Aug 02, 2021 4:50 pm
It seems like an issue that NASA and others are well-advised to consider in the realm of space exploration. We haven't had much experience with the harmful effects in our lives on Earth. Not too many people have found themselves subjected to harmful infrasound, happily. And in some cases, one can detect it well enough to feel like leaving an area, and then that's what the people or animals do to avoid it. But in a space vessel, if some sufficiently intense infrasound were to arise from the mechanics of the craft, the astronauts might have no means of detecting it, no way of escaping it, and long exposure to it. I guess that's just one more happy thing for them to worry about.

neufer wrote: ↑Mon Aug 02, 2021 2:53 pm

• z = 0.96 => F♯4 (370 Hz) => 10.6 Gly (comoving radial distance)
  
  z = 1089 => 0.666 Hz => Cosmic Microwave Background

https://en.wikipedia.org/wiki/Infrasound wrote:
. . . Air is a very inefficient medium for transferring low frequency vibration from a transducer to the human body. Mechanical connection of the vibration source to the human body, however, provides a potentially dangerous combination. The U.S. space program, worried about the harmful effects of rocket flight on astronauts, ordered vibration tests that used cockpit seats mounted on vibration tables to transfer "brown note" and other frequencies directly to the human subjects. . . .

JohnM wrote: ↑Mon Aug 02, 2021 2:27 pm I have found about 6 at 13.1 but nothing further than that it's difficult to find the deepest one visible as I am not sure what image they have used. It would also help if the JPEG image file had an astrometric calibration so it could be opened in Astronomy Data explorers such as Aladin