You’ve seen the James Webb Space Telescope’s first full-color images, right? A stellar nursery revealing previously invisible stars, a giant exoplanet’s atmosphere examined, a group of galaxies, a beautiful planetary nebula and the deepest image of our universe ever captured.
Pretty cool, huh? But were they real?
Of course they were real!
Were they exactly as Webb captured them in one single image, like you taking a photo with your phone?
No—not at all.
Webb is designed to be sensitive to light that we cannot see. It also has four science instruments and seventeen modes.
“When you get the data down, they they don’t look anything like a beautiful color image,” said Klaus Pontoppidan, Webb project scientist at STScI, who heads-up a team of 30 expert image manipulators. “They don’t hardly look like anything at all [and] it’s only if you know what to look for that you can appreciate them.”
Webb’s engineers had to heavily manipulate the images we saw a lot before they were published, and for some pretty simple and common-sense reasons.
So what’s going on?
This is not just snapping a picture on a phone.
Planning the images
First comes the shot selection. NASA was looking for objects that would produce a nice frame, have structure and make use of color—while also highlighting science.
Webb cannot see every part of the sky at any given time. So given that the launch of the telescope was delayed multiple times, there was no way that engineers could meticulously plan the first images until Webb went to skywards last December.
When it did so, engineers had a list of about 70 targets, which were selected to demonstrate the breadth of science web was capable of, and which could herald spectacular colour images.
“Once we knew when we would be able to take the data, we could go down that list and pick the highest prioritized targets that were visible at that time,” said Pontoppidan. “The images were planned for a long time [and] there's been a lot of work going into stimulating what the observations would look like so that everything could be configured just right.”
The Carina Nebula, as captured by the James Webb Space Telescope (JWST). NASA, ESA, CSA, and STScI
How Webb’s data gets back to Earth
Before engineers can get to work manipulating Webb’s images the raw data has to be returned to our planet from a million miles away in space. That's done by using NASA JPL’s Deep Space Network (DSN), which is how engineers communicate with, and receive data from, its 30+ robotic probes in the solar system and beyond—including Webb. There are three complexes in the DSN, each placed 120º from each other; California, Madrid in Spain and Canberra in Australia.
Radio waves are very dependable, but slow. The data comes in at a ponderous couple of megabits per second (Mbps). However, the DSN will soon be upgraded from slow radio transmissions to super-fast “space lasers” that could massively increase data rates to as much as 10 or even 100 times faster.
“We plan things out, upload them to the observatory, take the data and get them back down on Earth—then we have another long period of time where we process the data,” said Pontoppidan.
Why the colors in Webb’s photos are fake
Are the Webb telescope images colorized? Are the colors in space photos real? No, they are not. The Webb telescope sees in red. It’s up there specifically to detect infrared light, the faintest and farthest light in the cosmos.
It essentially sees in heat radiation, not visible light. It sees another part of the electromagnetic spectrum:
Electromagnetic Spectrum, The Visible Range (Shaded Portion) Is Shown Enlarged On The Right. (Photo ... [+]
Think of a rainbow. At one end is red at the other end is blue or violet. That rainbow is, in reality, much wider, but both extremes represent the limits to what colors the human eye can perceive. Beyond blue are shorter and shorter wavelengths of light that we have no names for. Ditto beyond red, where the wavelength of light gets longer.
That’s where Webb is looking—the infrared part of the electromagnetic spectrum.
It uses masking techniques—filters—to allow it to detect faint sources of light next to very bright ones. But none of it is in “color.”
So how can the photos we see possibly be in color for us?
How Webb’s photos are colorized
Webb’s images are moved up the electromagnetic spectrum from a part we can’t perceive into the visible light part that we can see.
They take mono brightness images from Webb using up to 29 different narrowband filters, each of which detects different wavelengths of infrared light. They them assign each filter’s collected light a different visible color, from the reddest red light has the longest wavelength) to blue (which has the shortest wavelength). They then create a composite image.
Is that cheating? All the engineers are doing is taking radiation from one part of the spectrum our eyes can’t see and shifting it into another part of the spectrum we can see.
It’s like playing a song in a different key.
Besides, all cameras—including your smartphone’s camera—use filters to take the images you see. No, not Instagram filters, but individual red, green and blue filters that, when combined, produces a visible image that looks “real.”
If you think Webb’s images are not real then you also have to think that your own smartphone’s photos are fake.
Galaxy cluster SMACS 0723, known as Webb’s First Deep Field, features "spiky" stars and even ... [+]
How long it takes to process Webb’s images
It’s a complex process that for data from Webb just hadn’t been done before. So it takes a few weeks for each image to emerge in their full colorful glory.
“Typically, the process from raw telescope data to final, clean image that communicates scientific information about the universe can take anywhere from weeks to a month,” said Alyssa Pagan, a science visuals developer at STScI.
It was surely worth the wait.
“In the first images we have just a few days worth of observations,” said Pontoppidan. “This is really only the beginning and we're only scratching the surface.”
Wishing you clear skies and wide eyes.
https://news.google.com/__i/rss/rd/articles/CBMigwFodHRwczovL3d3dy5mb3JiZXMuY29tL3NpdGVzL2phbWllY2FydGVyZXVyb3BlLzIwMjIvMDcvMTgveWVzLW5hc2EtZGlkLW1hbmlwdWxhdGUtdGhlLXdlYmItdGVsZXNjb3Blcy1maXJzdC1jb2xvci1pbWFnZXMtbGFzdC13ZWVrL9IBAA?oc=5
2022-07-19 00:00:00Z
1478465385
Tidak ada komentar:
Posting Komentar