James Webb Space Telescope

[Parson]

My guess is that there is a certain amount of redundancy built in - if a few pulleys malfunction the others can take over their job in order to ensure the tasks get done,. and vice versa. The whole project isn't a bust just because one pulley motor doesn't work.

Maybe, but it was said that there were 300 something single point failures, that if this one thing didn't work as planned the mission was a bust. And I know that several of those were part of the unfolding.

 

[Venusian Broon]

Okay, here's something I don't understand.

The Webb telescope will be able to pick up signals from the earliest time in the formation of the universe. Those signals have been traveling towards us for billions of years. That means we're billions of light-years away from the source of the signals. How, if we aren't traveling at the speed of light, has there been enough time for us to get so far away?

Or to put it another way, if those signals are traveling at the speed of light, how come they didn't pass us years ago? How come they're only just catching up with us now?

Assuming that the big bang and current standard model we are using at the moment, is more or less correct...

...currently our estimate for the size of the observable universe is a sphere with a radius of about 46 billion light years around us. Which you will note is much bigger than 13.8 billion - which is roughly our estimate for the age of the universe. How can we see something 46 billion light years away if there has only been 13.8 billion years?

This disparity is caused by the expansion of the universe, which has been continually occurring since the start (very fast right at the start with inflation - a long bit of slower expansion afterwards - and, we currently believe, dark energy now accelerating it)

This expansion has two impacts. First, it increases the distance between objects and the bigger the distance between the two objects the faster the expansion - this expansion is a function of space-time, not a force on matter and photons etc. And space-time does not need to observe the constraint of the speed of light. Thus we suspect that the real universe is many times bigger than we can observe, because beyond a certain point the very distant universe would be expanding so fast that light emitted in a very distant part would never be able to reach us.

The second is that any photons emitted will get 'stretched' by this expansion and become red-shifted. Thus the earliest 'object' we can see is the cosmic microwave background radiation, which is the burst of light that decoupled when the universe cooled enough for neutral hydrogen to form - about 370,000 years after the big bang. At the time I believe it was a blackbody radiation at about 3000K. It is now a blackbody radiation of about 2.7K. In wavelength terms the photons have been stretched just over 1000 times in wavelength.

Thus the possibility that the James Webb telescope might see objects that formed in the very early universe - such as population III stars, because all the light emitted at that time will have been redshifted to infrared/microwave.


So TL;DR:

The expansion of the universe means that we are only now getting light from certain parts of the universe, and it is these areas that we can see as they were at the earliest times.

Confusingly these areas are now much further away in real distance than the lifetime of the universe, but this can be accounted for by the expansion of the universe as well.


If you want a simple analogy. Think of a balloon that can be blown up indefinitely. Mark two spots on it. They are, say, galaxies A and B. The expansion of the universe is this balloon inflating constantly and getting bigger. As it does so the distance between A and B gets bigger. Now train an ant to walk between A and B at a constant speed - think of that as a photon being emitted from A towards B! As the expansion increases the distance the ant is still stuck at walking at the same speed, therefore will take longer to reach B.

 

[mosaix]

Assuming that the big bang and current standard model we are using at the moment, is more or less correct...

...currently our estimate for the size of the observable universe is a sphere with a radius of about 46 billion light years around us. Which you will note is much bigger than 13.8 billion - which is roughly our estimate for the age of the universe. How can we see something 46 billion light years away if there has only been 13.8 billion years?

This disparity is caused by the expansion of the universe, which has been continually occurring since the start (very fast right at the start with inflation - a long bit of slower expansion afterwards - and, we currently believe, dark energy now accelerating it)

This expansion has two impacts. First, it increases the distance between objects and the bigger the distance between the two objects the faster the expansion - this expansion is a function of space-time, not a force on matter and photons etc. And space-time does not need to observe the constraint of the speed of light. Thus we suspect that the real universe is many times bigger than we can observe, because beyond a certain point the very distant universe would be expanding so fast that light emitted in a very distant part would never be able to reach us.

The second is that any photons emitted will get 'stretched' by this expansion and become red-shifted. Thus the earliest 'object' we can see is the cosmic microwave background radiation, which is the burst of light that decoupled when the universe cooled enough for neutral hydrogen to form - about 370,000 years after the big bang. At the time I believe it was a blackbody radiation at about 3000K. It is now a blackbody radiation of about 2.7K. In wavelength terms the photons have been stretched just over 1000 times in wavelength.

Thus the possibility that the James Webb telescope might see objects that formed in the very early universe - such as population III stars, because all the light emitted at that time will have been redshifted to infrared/microwave.


So TL;DR:

The expansion of the universe means that we are only now getting light from certain parts of the universe, and it is these areas that we can see as they were at the earliest times.

Confusingly these areas are now much further away in real distance than the lifetime of the universe, but this can be accounted for by the expansion of the universe as well.


If you want a simple analogy. Think of a balloon that can be blown up indefinitely. Mark two spots on it. They are, say, galaxies A and B. The expansion of the universe is this balloon inflating constantly and getting bigger. As it does so the distance between A and B gets bigger. Now train an ant to walk between A and B at a constant speed - think of that as a photon being emitted from A towards B! As the expansion increases the distance the ant is still stuck at walking at the same speed, therefore will take longer to reach B.

Excellent. Many thanks.

 

[mosaix]

Nasa begins months-long effort to focus James Webb space telescope

The revolutionary new scope could provide a glimpse of the cosmos dating back billions of years, but first some painstaking adjustments are needed

www.theguardian.com

 

[Pyan]

Well, it's finally in the right place, at least. Just hope that all the final unfolding goes to plan!

James Webb telescope parked in observing position

The $10bn successor to Hubble is parked a million miles from Earth after a 30-day journey from Earth.

www.bbc.co.uk

 

[Foxbat]

Just another five months to go until we get the first result…talk about long exposure

 

[BT Jones]

Facebook asked me if I wanted to join a FB group on the JWT. Irrespective of how it ascertained my interest (presumably somehow accessing the stories I read on the BBC website), I said yes.

Really looking forward to some stunning images.

 

[Venusian Broon]

Nice summary of what to expect from the telescope

 

[mosaix]

I receive a notification from the New Scientist app that the telescope has sent back its first picture - of itself. Disappointingly the New Scientist website has no further info and I can't find anything related on the web.

Anyone heard anything?

Update: just found this:

James Webb Space Telescope just sent back its first image - of itself

NASA engineers working to align the 18 hexagonal mirrors of the James Webb Space Telescope have released its first pictures. One shows the same star appearing 18 times, while a camera also took a 'selfie' of the mirrors

www.newscientist.com

 

[Venusian Broon]

I receive a notification from the New Scientist app that the telescope has sent back its first picture - of itself. Disappointingly the New Scientist website has no further info and I can't find anything related on the web.

Anyone heard anything?

Update: just found this:

James Webb Space Telescope just sent back its first image - of itself

NASA engineers working to align the 18 hexagonal mirrors of the James Webb Space Telescope have released its first pictures. One shows the same star appearing 18 times, while a camera also took a 'selfie' of the mirrors

www.newscientist.com

All my astronomy channels are going full tilt! Dr Becky here explains in a bit more depth:

 

[Elckerlyc]

Well, 18 mirrors, 18 stars. That's good news.

 

[Parson]

Yes, only good news here. This is such an impressive feat of engineering it boggles the mind.

 

[Stephen Palmer]

Amazing. Good news indeed.

 

[Foxbat]

A somewhat frivolous question but is this Webb selfie the furthest selfie taken in space? Or did Voyager have a selfie capability?

 

[Elckerlyc]

Selfies weren't invented yet in those days.

 

[Venusian Broon]

A somewhat frivolous question but is this Webb selfie the furthest selfie taken in space? Or did Voyager have a selfie capability?

I think not. But I don't think Voyager had the ability to take pictures that had itself in it.

But, I'm pretty sure a Venus probe took a selfie of itself...Just checked, it took it while passing Venus, it was on way to Mercury!

BepiColombo Spacecraft Headed for Mercury Takes a Photo with Venus Along the Way

The European-Japanese spacecraft BepiColombo has taken a selfie with Venus on its way to another planet, Mercury.

www.techtimes.com

Another Japanese mission that was there to test solar sails (and also in the vicinity of Venus I believe, and I think this was the one I was thinking of) also had a small camera orbit the spacecraft and took piccies

Mini-camera pictures Japan's Ikaros solar sail

A small free-floating camera returns images of Japan's solar sail, Ikaros, in flight.

www.bbc.co.uk

What about the rovers on Mars? They are probably, in general, further away from Earth.

 

[Parson]

The Mars rovers are much further from earth.

 

[Lumens]

Does the Pale Blue Dot picture qualify as a selfie?

The Pale Blue Dot - Revisited - NASA Science

The Pale Blue Dot is a photograph of Earth taken Feb. 14, 1990, by NASA’s Voyager 1 when it was 3.7 billion miles (6 billion kilometers) from the Sun.

solarsystem.nasa.gov

 

[Justin Swanton]

Does the Pale Blue Dot picture qualify as a selfie?

The Pale Blue Dot - Revisited - NASA Science

The Pale Blue Dot is a photograph of Earth taken Feb. 14, 1990, by NASA’s Voyager 1 when it was 3.7 billion miles (6 billion kilometers) from the Sun.

solarsystem.nasa.gov

Of course! A long selfie stick...

 

[mosaix]

Spacewatch: Nasa’s Webb telescope mirror alignment continues

Seven-step process to enable segments to work as a single mirror nears halfway point

www.theguardian.com

Three of the seven stages of mirror alignment completed.