The James Webb Space Telescope

[bilby]

How long is a day or a year when there’s no earth or sun? How long is a second in a universe composed of only hydrogen and helium?

How fast is a car with no speedometer? The ability (or inability) to measure a fundamental property isn't a requirement for that property to exist. Taking the speedometer out of your car won't stop you from getting a ticket.

This isn't a case of no speedometer, but the lack of the concept. A year is the time it takes to go around the primary--if there's no primary there is no duration spent going around it.

But that's not the definition of a year, it's just the origin of it. A year is 60x60x24x365.25 seconds.

 

[Elixir]

How long is a day or a year when there’s no earth or sun? How long is a second in a universe composed of only hydrogen and helium?

How fast is a car with no speedometer? The ability (or inability) to measure a fundamental property isn't a requirement for that property to exist. Taking the speedometer out of your car won't stop you from getting a ticket.

This isn't a case of no speedometer, but the lack of the concept. A year is the time it takes to go around the primary--if there's no primary there is no duration spent going around it.

But that's not the definition of a year, it's just the origin of it. A year is 60x60x24x365.25 seconds.

And a second is based on cesium atoms, which did not exist in the early universe.

 

[Jimmy Higgins]

How long is a day or a year when there’s no earth or sun? How long is a second in a universe composed of only hydrogen and helium?

How fast is a car with no speedometer? The ability (or inability) to measure a fundamental property isn't a requirement for that property to exist. Taking the speedometer out of your car won't stop you from getting a ticket.

This isn't a case of no speedometer, but the lack of the concept. A year is the time it takes to go around the primary--if there's no primary there is no duration spent going around it.

But that's not the definition of a year, it's just the origin of it. A year is 60x60x24x365.25 seconds.

And a second is based on cesium atoms, which did not exist in the early universe.

A second these days is the amount of time it requires light to pass a distance of 299,792,458 meters in a vacuum (bagless).

 

[Swammerdami]

This telescope is a splendid tribute to science and humanity. A thousand years from now much will be forgotten, but memory of this telescope should live on.

How long is a day or a year when there’s no earth or sun? How long is a second in a universe composed of only hydrogen and helium?

How fast is a car with no speedometer? The ability (or inability) to measure a fundamental property isn't a requirement for that property to exist. Taking the speedometer out of your car won't stop you from getting a ticket.

This isn't a case of no speedometer, but the lack of the concept. A year is the time it takes to go around the primary--if there's no primary there is no duration spent going around it.

But that's not the definition of a year, it's just the origin of it. A year is 60x60x24x365.25 seconds.

And a second is based on cesium atoms, which did not exist in the early universe.

A second these days is the amount of time it requires light to pass a distance of 299,792,458 meters in a vacuum (bagless).

As self-appointed Nitpicker-in-Chief, I shall pick some nits.

(1) While I'm delighted you specified that the vacuum be bagless, you're headed for circularity since the meter is defined to be the reciprocal of your definition of a second. I think the pedants still define the second via cesium atom as Mr. Elixir states. If you don't have any cesium atoms handy then you might be able to time things with your Rolex Pearlmaster. But I wouldn't recommend the $9 Rolex I picked up in Pattaya.

(2) 60x60x24x365.24 is a better approximation than 60x60x24x365.25 for the duration of a year. My cite is Gregory XIII, the 226th Infallible Vicar of Christ. But add as many sig figs as you wish and you won't have a definition for the year. Trick Question: About how many times does Orion's belt approach the zenith at Singapore in an average year?

(3) On the topic of measuring time in the very early or very late universe I considered a link to Roger Penrose's famous but peculiar insights. But, like Eisenhower's failed effort in September 1944, that would involve picking a Nit Too Far.

 

[Jimmy Higgins]

This telescope is a splendid tribute to science and humanity. A thousand years from now much will be forgotten, but memory of this telescope should live on.

How long is a day or a year when there’s no earth or sun? How long is a second in a universe composed of only hydrogen and helium?

How fast is a car with no speedometer? The ability (or inability) to measure a fundamental property isn't a requirement for that property to exist. Taking the speedometer out of your car won't stop you from getting a ticket.

This isn't a case of no speedometer, but the lack of the concept. A year is the time it takes to go around the primary--if there's no primary there is no duration spent going around it.

But that's not the definition of a year, it's just the origin of it. A year is 60x60x24x365.25 seconds.

And a second is based on cesium atoms, which did not exist in the early universe.

A second these days is the amount of time it requires light to pass a distance of 299,792,458 meters in a vacuum (bagless).

As self-appointed Nitpicker-in-Chief, I shall pick some nits.

(1) While I'm delighted you specified that the vacuum be bagless, you're headed for circularity since the meter is defined to be the reciprocal of your definition of a second. I think the pedants still define the second via cesium atom as Mr. Elixir states. If you don't have any cesium atoms handy then you might be able to time things with your Rolex Pearlmaster. But I wouldn't recommend the $9 Rolex I picked up in Pattaya.

You are incorrect. A meter is something that measures something, like the implausibility of my statements. You line 299,792,458 of those meters in a row, and then time how long it takes light in a bagless vacuum to transit that distance.

For a truly enlightened understanding on standardization of measurements, watch this short.

 

[lpetrich]

It's actually time that's the fundamental unit, the one that everything else is defined in terms of. The second is 9,192,631,770 times the period of the hyperfine-transition spectral line of cesium-133 atoms in their ground state. It was earlier defined in terms of the year, and before that, the day.

Length is defined by fixing the speed of light in a vacuum, mass by fixing the quantum-mechanical scale constant (Planck's constant), and temperature by fixing the thermodynamic scale constant (Boltzmann's constant).

 

[lpetrich]

Webb Continues Multi-Instrument Alignment – James Webb Space Telescope

While telescope alignment continues, Webb’s Mid-Infrared Instrument (MIRI) is still in cooldown mode. MIRI, which will be the coldest of Webb’s four instruments, is the only instrument that will be actively cooled by a cryogenic refrigerator, or cryocooler. This cryocooler uses helium gas to carry heat from MIRI’s optics and detectors out to the warm side of the sunshield. To manage the cooldown process, MIRI also has heaters onboard, to protect its sensitive components from the risk of ice forming. The Webb team has begun progressively adjusting both the cryocooler and these heaters, to ensure a slow, controlled, stable cooldown for the instrument. Soon, the team will turn off MIRI’s heaters entirely, to bring the instrument down to its operating temperature of less than 7 kelvins (-447 degrees Fahrenheit, or -266 degrees Celsius).

In the meantime, after achieving alignment with the Near-Infrared Camera (NIRCam), Webb engineers have begun aligning the telescope to the remaining near-infrared instruments.

NASA Webb Telescope on Twitter: "Webb’s alignment progress continues! Last in the instrument “align-up” is MIRI, which will be coolest at 7 K (-447 F or -266 C). You might expect MIRI to have a special refrigerator, but did you know its cooldown process also involves heaters? Learn why: (link)" / Twitter

 

[lpetrich]

That telescope alignment evaluation image shows a relatively bright star amidst a lot of faint ones and galaxies. I'm sure that its orange and yellow colors are false colors for our convenience, like for that galaxy-center black-hole image a few years back.

The star image has six long spikes coming out of it, and that's from diffraction of light. The spikes come from the straight edges of the mirror segments, and I've verified that with calculations.

 

[Loren Pechtel]

That telescope alignment evaluation image shows a relatively bright star amidst a lot of faint ones and galaxies. I'm sure that its orange and yellow colors are false colors for our convenience, like for that galaxy-center black-hole image a few years back.

The star image has six long spikes coming out of it, and that's from diffraction of light. The spikes come from the straight edges of the mirror segments, and I've verified that with calculations.

How could they not be false colors? It's not looking at colors we can see in the first place!

 

[lpetrich]

That telescope alignment evaluation image shows a relatively bright star amidst a lot of faint ones and galaxies. I'm sure that its orange and yellow colors are false colors for our convenience, like for that galaxy-center black-hole image a few years back.

How could they not be false colors? It's not looking at colors we can see in the first place!

True, but those colors make it seem more like our usual visual perception than a grayscale image would -- we see in colors, not grayscale, except for people with only one kind of retina cone cell.

 

[lpetrich]

NASA Webb Telescope on Twitter: "To chill to its operating temperature of less than 7 K (-447 F or -266 C), ..." / Twitter

To chill to its operating temperature of less than 7 K (-447 F or -266 C), Webb’s MIRI instrument uses a special refrigerator. But it also requires heaters to control its cooldown & prevent ice from forming in space.

Wait, ice? Allow us to explain (thread

When Webb launched, moist air was entrapped between components like the sunshield membranes and its many layers of insulation. Other Webb materials absorbed water vapor from Earth’s atmosphere. Most of this air escaped just 200 seconds after liftoff, but some moisture remained.

Water behaves differently in space than on the ground. In a perfect vacuum, water can exist only as a gas, but even space isn’t a perfect vacuum. Instead, water tends to "outgas" at temperatures above 160 K (-172 F or -113 C), and it tends not to below 140 K (-208 F or -133 C). Crucially, if any water molecules are floating around and contact a surface colder than 140 K, they will stick to it as ice and never come off. This is what’s incredibly important to prevent for the Webb telescope.

Once Webb’s sunshield deployed, Webb began to cool quickly. Our team carefully managed the rate of this cooldown and the order in which different components cooled using electric strip heaters. This allowed water to escape to space rather than freeze onto sensitive components. MIRI’s “refrigerator,” or cryocooler, uses helium gas to carry heat out to the warm side of Webb’s sunshield. To ensure that the cryocooler could work & MIRI could cool to its ultimate temperature, all water had to be either eliminated or purposely contained in designated areas.

NEW on our “Where is Webb” tracker: You can now track MIRI’s temperature as it cools to its target level! Also check out our interactive graphs to see how the temperatures of Webb’s instruments have changed since launch: (link) #UnfoldTheUniverse

Where Is Webb? NASA/Webb

Why the heaters? Hhey had to keep the instruments warm enough to keep water from condensing on them until all the water had outgassed.

 

[lpetrich]

"Where is Webb?" now has temperature graphs.

• Sunshield structure: 324 K - 51 C
• Spacecraft bus: 287 K - 14 C
• Primary mirror: 42 K
• Instrument radiator: 37 K

The spacecraft bus has been at nearly constant temperature since the launching of the spacecraft.

The sunshield structure was originally -7 C at 4 days after launch because of its stowed state keeping out sunlight, but at 7 days, after deployment, that structure reached its final temperature.

The primary mirror started off at a similar temperature, but by day 30, leveled off at 62 K. Then at day 37, it started declining again, reaching its final temperature at day 51.

The instrument radiator started off at 150 K, then declined to 73 K by day 12, started declining again at day 34, then settled down at its final value by day 57.

Among the instruments is the FSM, the Fine Steering Mirror. That's the fourth mirror on the way to the instruments (quaternary mirror?). That mirror and the tertiary mirror are part of the Aft Optics Subsystem, an elongated box mounted in the missing segment of the primary mirror.

The FSM started out at 207 K, then dropped quickly after day 36, reaching 79 K the next day, and then declining much more slowly and leveling off at around day 60. Its temperature is now 32 K.

The three near-IR instruments (NIRCam, NIRSpec, NIRSS) started off at 160 K, then after day 34, declined then leveled off at around 60 days, reaching 35 K.

MIRI started off at 150 K and slowly declined to 94 K at day 87, when its cryocooler was turned on. Its decline speeded up, and at day 103, it reached 5.6 K.

 

[lpetrich]

Webb Completes First Multi-Instrument Alignment – James Webb Space Telescope

The sixth stage of aligning NASA’s James Webb Space Telescope’s mirrors to its scientific instruments so they will create the most accurate and focused images possible has concluded. While the Mid-Infrared Instrument (MIRI) continues its cooldown, optics teams have successfully aligned the rest of the observatory’s onboard instruments to Webb’s mirrors.

NASA Webb Telescope on Twitter: "Now let's get in formation ..." / Twitter

Now let's get in formation

3 out of #NASAWebb's 4 instruments have been successfully aligned to its mirrors! This concludes the 6th stage of its 7 mirror alignment phases to create the most accurate & focused images possible: (link) #UnfoldTheUniverse (pic link)

Previous alignment efforts were so accurate that the team concluded no additional adjustments are necessary for Webb's secondary mirror until the seventh stage. This final stage will also involve Webb's MIRI instrument, the last instrument to be aligned, when it has fully cooled.

What's next? After our team makes final mirror alignment adjustments to ensure all 4 instruments are aligned, each instrument will then need individual calibration before our first science images #UnfoldTheUniverse this summer.

 

[lpetrich]

Webb’s Mid-Infrared Instrument Cooldown Continues – James Webb Space Telescope - that's MIRI

The cooldown must go through a "pinch point" at 15 K, when the cryocooler's ability to remove heat is at its lowest. Once it goes through that point, it will improve, and it will stay at 7 K for the rest of the mission.

NASA Webb Telescope on Twitter: "What’s cooler than being cool?

At less than 7 K (-447 F or -266 C), Webb’s MIRI instrument will be more than ice cold! Learn from @NASAJPL & @ESA_Webb team members about an upcoming critical point for MIRI and why it has to be so cold: (link) #UnfoldTheUniverse (pic link)" / Twitter

 

[lpetrich]

NASA Webb Telescope on Twitter: "You bet we’re turning it up: Our @NASA’s Curious Universe audio mini-series on the James Webb Space Telescope has been nominated for @TheWebbyAwards!

Hear us out on how you can help put the Webb in #Webby: (links)" / Twitter
Webby?
NASA Receives Eight 2022 Webby Award Nominations | NASA
"NASA's broad reach across digital platforms has been recognized by the International Academy of Digital Arts and Sciences, which gave NASA eight nominations for the academy's Webby Awards this year."

• First Woman - NASA's Promise For Humanity
• NASA's Curious Universe: A Day in Space
• NASA's Curious Universe: James Webb Mini-Series
• NASA's Global Climate Change
• NASA's Jet Propulsion Laboratory Virtual Tour
• NASA's Social Media: Creating a Community of Explorers
• NASA's Solar System Exploration
• "Snacktime with NASA"

NASA made substantial contributions to three other Webby nominees:

The Lego Build to Launch series, which Lego Education worked with NASA to create, is nominated for the Webby and People’s Voice Award for Virtual and Remote Health & Science Series.
National Geographic's Mars Rover Augmented Reality Experience with NASA is nominated for Best Use of Filters/Lenses.
Google's A Mars Rover Looks Back is nominated for Video - Branded Entertainment - Music and Social Video.

 

[lpetrich]

Webb’s Cool View on How Stars, Planets Form – James Webb Space Telescope

NASA Webb Telescope on Twitter: "Spring cleaning on your mind?

Webb will also be “dusting” in space! With its infrared vision, it will peer through cosmic dust to see how stars & planets form. More from @SpaceTelescope's Webb project scientist Klaus Pontoppidan: (link) #UnfoldTheUniverse (vid link)" / Twitter

 

[Loren Pechtel]

Why should we trust this telescope? It's awfully cold-hearted!

 

[lpetrich]

Webb Telescope’s Coldest Instrument Reaches Operating Temperature
MIRI, the mid-infrared instrument, is now at 6.4 K. It needs to be that cold to see mid-IR instead of the near-IR that the other instruments see.

NASA Webb Telescope on Twitter: "Cool news! Webb’s MIRI instrument ..." / Twitter

Cool news! Webb’s MIRI instrument recently passed through its critical “pinch point” and cooled to just a few kelvins above absolute zero, which is the coldest you can go: (link)

Wondering why MIRI is extremely chill? Thread

All of Webb’s instruments detect infrared light (which we feel as heat), so they need to be cold to seek out faint heat signatures in the universe. MIRI detects longer infrared wavelengths than the others, so it needs to be even colder. Webb also needs to be cold to suppress something called dark current, an electric current created by the vibration of atoms in its instrument detectors. Dark current can give the false impression that there is light from a cosmic object when there isn’t. Since temperature is a measurement of how fast atoms are vibrating, lowering temperature means less vibration and less dark current. MIRI’s ability to detect longer wavelengths makes it more sensitive to dark current, so it also needs to be colder to remove that effect.

Along with the other instruments, MIRI initially cooled with help from Webb’s sunshield. Unlike the others, the rest of its cooldown required a special cryocooler, along with heaters to prevent water ice. Yes, ice! (link to earlier tweet on that issue)

Many of you asked us why MIRI cooled down so slowly. Not only did the cooldown have to be carefully managed, but the cryocooler itself wasn’t turned on until mirror alignment was done, to keep extra vibrations from affecting the alignment process. The “pinch point,” MIRI’s transition from 15 K to less than 7 K, was especially challenging because it involved several time-sensitive operations to be performed in rapid succession. It could have determined whether MIRI would complete its cooldown…or begin warming instead. “We spent years practicing...running through the commands and the checks that we did on MIRI [...] When the test data rolled in, I was ecstatic to see it looked exactly as expected and that we have a healthy instrument.” - Mike Ressler, @NASAJPL’s MIRI project scientist

MIRI is a joint effort by @NASA and @ESA. Now that it is at operating temperature, MIRI team members will take test images to check its functionality. After all of Webb’s instruments are calibrated, expect Webb’s first science images to #UnfoldTheUniverse this summer!

 

[lpetrich]

Is Webb at Its Final Temperature? – James Webb Space Telescope

uring commissioning, Webb is currently spending most of its time pointed at the ecliptic poles, which is a comparatively hot attitude. During science operations, starting this summer, the telescope will have a much more even distribution of pointings over the sky. The average thermal input to the warmest mirror segments is expected to go down a bit, and the mirrors will cool a bit more.

Later in commissioning, we plan to test the thermal dependence of the mirrors on the attitude. We will point Webb at a hot attitude for several days, and point Webb at a cold attitude for several days, in a process called the thermal slew. This will inform us how long it takes for the mirrors to cool down or heat up when the observatory is at these positions for any given amount of time.

Is Webb at its final temperature? The answer is: almost!

Why might the ecliptic poles be relatively hot? I'm guessing that that's because those directions are near the plane of our Galaxy, with all the stars and interstellar material there.

NASA Webb Telescope on Twitter: "Is Webb at its final temperature? Almost! ..." / Twitter

Is Webb at its final temperature? Almost!

All of Webb’s instruments have reached their super cold operating temperatures, but the mirrors still have a bit of a ways to go. Remember: The colder the mirrors, the better we can #UnfoldTheUniverse! More: (link)

So what’s the hold-up?

Webb’s mirrors are made of beryllium. At the extremely cold temperatures Webb is facing, beryllium has a long thermal time constant, meaning it takes a long time to cool. Don’t worry: Beryllium holds its shape so well at cold temperatures that further cooling won’t affect the alignment process, and will in fact only enhance our super-cold Mid-Infrared Instrument’s performance.

When we point Webb at a target, the mirrors and sunshield move together. Once science operations start, Webb’s changing angle in relation to the Sun will also help keep its mirrors colder on average.

 

[lpetrich]

NASA’s Webb In Full Focus, Ready for Instrument Commissioning – James Webb Space Telescope
Complete with pictures from JWST's 4 instruments. They look in slightly different directions, and they can all be run at the same time.

NASA Webb Telescope on Twitter: "“It’s full of stars!” This mosaic represents a sparkling turning point as we #UnfoldTheUniverse. #NASAWebb’s mirrors are now fully aligned! Next is instrument calibration, the final phase before Webb is ready for science: https://t.co/PcAxajyMfI What do we see here? https://t.co/qzdZRbsgRF" / Twitter

“It’s full of stars!”

This mosaic represents a sparkling turning point as we #UnfoldTheUniverse. #NASAWebb’s mirrors are now fully aligned! Next is instrument calibration, the final phase before Webb is ready for science: (link)

What do we see here?

First, a quick breakdown. “Fully aligned” means that Webb’s mirrors are now directing fully focused light collected from space down into each instrument. Each instrument is also successfully capturing images with the light being delivered to them.

In this mosaic, each engineering image is a demonstration that one of Webb’s instruments is fully aligned with the telescope and in focus. In view is a part of the Large Magellanic Cloud, a small, irregular satellite galaxy of the Milky Way. The sizes & positions of the images represent the relative arrangement of each of Webb’s instruments in the plane where the telescope focuses light. In comparing the images, you may see that each instrument points at a slightly offset part of the sky relative to the rest.

Like our last engineering image, this mosaic is in a red color palette that was chosen to optimize visual contrast. As a reminder, colors in space telescope images sometimes recreate the way our eyes see; other times they are selected to highlight features of an object.

Let's turn the sound up…we think it's time for an instrument round up!

Webb’s imaging instruments are NIRCam, NIRISS and MIRI. MIRI sees in mid-infrared light instead of near-infrared like the others, so you can see interstellar clouds as well as starlight in its image!

NIRSpec is a spectrograph, not an imager, but it can take images for calibrations & target acquisition. See those dark bands? They're due to structures of its microshutter array — tiny “window” shutters that can be opened or shut to capture data from 100 objects simultaneously.

Bundled together with NIRISS is Webb’s Fine Guidance Sensor (FGS), which tracks guide stars to point the observatory accurately and precisely. Its 2 sensors are not generally used for scientific imaging but can take calibration images like these.

The optical performance of the telescope continues to be better than the engineering team’s most optimistic predictions. From this point forward the only changes to the mirrors will be very small, periodic adjustments to the primary mirror segments.

During Webb’s next & final step, instrument calibration, each instrument’s specialized tools (masks, filters, lenses, etc.) will be configured and operated in various combinations. This will allow us to confirm their readiness for science operations this summer.