Any Astronomy Buffs Here?

[DevilHorse]

Here is an interesting website for those of you who are interested in what is going on with the Sun:
https://spaceweather.com/

Keeping close count of days with (without) sunspots, and some sense of where we are in the sunspot cycle, will give you a head start on planning when you take that trip to Alaska to see the Aurora.

There is also information on the latest near earth asteroids (that could be raining down on our heads).

Larry
DevilHorse

[swood1000]

"They say that the expansion of the universe results in expansion of the frequency of light travelling through it, so that what was originally visible light gets turned into infrared. Therefore, it seems like some of the infrared detected by JWST should be able to be directly mapped back to its original colors. "

I have no idea what the above statement means or who "They" are, but I could only guess.

• Is it talking about Red Shift as a result of the supposed Big Bang?
• The weeding out of higher frequencies due to space dust (not unlike what makes the sky blue)?
• Some change in the frequency due to dark matter acceleration?

One thing is for sure, the effect will be different depending on how far the thing you are looking at is. That information is difficult to determine unless you are just looking at Red Shift or using some other known technique (i.e., pulsar in a galaxy or supernova).

In either case, you might not know what function is needed to convert the less visible to the more visible.
It doesn't really matter, you just want a nice picture where similar structures, with similar textures get similar hues and tints (call Ted Turner).

Larry
DevilHorse

I was describing a Cosmological redshift, as distinct from a Doppler redshift. From an article on the subject:

In fact, only in the first case (a nearby body moving away from the earth) is the redshift caused by the Doppler effect. You've experienced the Doppler effect if you've ever had a train go past you and heard the whistle go to a lower pitch (corresponding to a longer wavelength for the sound wave) as the train moves away. The Doppler effect can happen for light waves too (though it can't be properly understood without knowing special relativity). It turns out that just like for sound waves, the wavelength of light emitted by an object that is moving away from you is longer when you measure it than it is when measured in the rest frame of the emitting object.

In the case of distant objects where the expansion of the universe becomes an important factor, the redshift is referred to as the "cosmological redshift" and it is due to an entirely different effect. According to general relativity, the expansion of the universe does not consist of objects actually moving away from each other - rather, the space between these objects stretches. Any light moving through that space will also be stretched, and its wavelength will increase - i.e. be redshifted. …

Practically speaking, the difference between the two (Doppler redshift and cosmological redshift) is this: in the case of a Doppler shift, the only thing that matters is the relative velocity of the emitting object when the light is emitted compared to that of the receiving object when the light is received. After the light is emitted, it doesn't matter what happens to the emitting object - it won't affect the wavelength of the light that is received. In the case of the cosmological redshift, however, the emitting object is expanding along with the rest of the universe, and if the rate of expansion changes between the time the light is emitted and the time it is received, that will affect the received wavelength. Basically, the cosmological redshift is a measure of the total "stretching" that the universe has undergone between the time the light was emitted and the time it was received.

For purposes of mapping redshifted light back to its original colors, however, I guess there wouldn’t be any difference between the two.

[swood1000]

This page talks about the difficulty distinguishing between Doppler, Gravitational and Cosmological redshifts.

[-jk]

You're overthinking the Ted Turner process. I think the color mapping is primarily to make the details stand out. And to be pretty so as to wow the masses and keep money flowing to Big Science.

I don't think they really try to present the pictures as they might have been seen by a naked human eye in some cosmological twist of fate.

-jk

[DevilHorse]

You're overthinking the Ted Turner process. I think the color mapping is primarily to make the details stand out. And to be pretty so as to wow the masses and keep money flowing to Big Science.

I don't think they really try to present the pictures as they might have been seen by a naked human eye in some cosmological twist of fate.

-jk

I totally agree with you, an in fact I prefer it. And frankly, it just looks nice on a wall or desktop. The "pretty pictures" provide the contrast to appreciate the structures of what you're looking at, where the center and edges could be of very different magnitudes. In reality, trying to get one exposure of something to see the whole thing is really hard, as anyone that has tried to take a photograph of something distantly astronomical, or faint, can attest.

I once tried to take a plate (does that date me?) of the Andromeda galaxy, and only got the center; so I'd have to overexpose the center to get the fine elements of the outer parts (at least with the telescope I was using). So composite pictures and color manipulation are part of the arsenal. As long as the originator is being faithful to what is being constructed, I have no problem with it. A picture is somewhat different than measurements (usually).

Larry
DevilHorse

[DevilHorse]

I was describing a Cosmological redshift, as distinct from a Doppler redshift. From an article on the subject:



For purposes of mapping redshifted light back to its original colors, however, I guess there wouldn’t be any difference between the two.

Interesting stuff. I was wondering how one would untangle the two different components of the Red Shift because they see only one 'shift' and have to attribute it to 2 factors; the speed of the emitting object and the distance of the emitting object. The information on both is not easily obtainable unfortunately. Sometimes you can tell by assuming what you're looking at is traveling with the stars/galaxies in the immediate proximity, or in the case of galaxies, you see stars that have known behaviors and can tell distances (pulsars, variable stars, novas).

I found this article that goes into slightly more detail on it, with a 'cartoon' like example at the bottom.
https://astronomy.swin.edu.au/cosmos...gical+redshift

Still not obvious to me that every object that is viewed by JWST will be able to tell all of these metrics. Some distant objects maybe galaxies, but will not be able to resolve individual stars, making it hard to tell distance other than just one redshift to work with. But then, the scientists are clever and there may be more information there than I understand.

Larry
DevilHorse

[swood1000]

Yes, an important purpose of these images is to keep the public interested, which they hope will keep the money flowing to NASA. And nobody is going to be complaining about the colors chosen as long as they make a pretty picture.

It turns out that when we are shown pictures of Saturn taken by Hubble the image is shown in “true color,” which is how the planet would look to us up close. However, for images of distant entities they are not that interested in how the object would look to us with our eyes. They are more interested in differentiating the different chemical elements that are of scientific interest, so they assign colors to represent those elements. For example, the first image below is the one that was distributed. According to the video below, the version on the right is how it would actually look to us with our eyes:

FalseColorPOC.jpgTrueColorPOC.jpg

I suppose it doesn’t hurt if they assign colors that produce a much more visually striking image.

Here’s a short and interesting explanation:

[moonpie23]

i don't mind the coloring...

[DevilHorse]

Perhaps some of you have seen some of my pointers in the Did you see that? thread on the Tonga Volcano and Tsunami this morning.

Here is something interesting relating to 15 minute altimiter readings in the US after the blast:
https://twitter.com/i/status/1482436390105272320

The shockwave from the Tonga-Hunga volcano propagated around the world, just like the Tsunami:
https://twitter.com/i/status/1482234507193466884

Larry
DevilHorse

[DevilHorse]

Perhaps some of you have seen some of my pointers in the Did you see that? thread on the Tonga Volcano and Tsunami this morning.

Here is something interesting relating to 15 minute altimiter readings in the US after the blast:
https://twitter.com/i/status/1482436390105272320

The shockwave from the Tonga-Hunga volcano propagated around the world, just like the Tsunami:
https://twitter.com/i/status/1482234507193466884

Larry
DevilHorse

More detailed discussion of why this Tonga-Honga volcano explosion was so explosive:
https://www.rnz.co.nz/news/on-the-in...jqstEvGwc62SYg

Larry
DevilHorse

[DevilHorse]

JWST has deployed ALL mirrors:
https://www.space.com/james-webb-spa...rrors-deployed

In 3 days, insertion into L2 orbit.
Then several months of twiddling the knobs to get ready for real work.

Larry
DevilHorse

[-jk]

Thanks. I still enjoy peeking at the Webb deployment site. (Thanks to whoever posted it first!)

The hot side is 57C (134F) and the cold side is down to -207C (-340F). Huge differential from a few layers of fancy fabric.

-jk

[swood1000]

Another interesting thing shown in graphs of JWST’s orbit around L2 is that it will not be directly over L2 but will be slightly closer to the Earth/Sun. The major reason is that JWST will be constantly subject to radiation pressure from the Sun, pushing it outward. Also it will be subject to the gravitation of the outer planets. However, its thrusters have to be on the opposite side of the sunshield from the telescope and instruments so as not to contaminate the cold side with unwanted heat or with rocket exhaust that could condense on the cold optics. If JWST ever had to thrust itself back in toward the Sun it would have to turn around and expose all the instruments to the Sun, frying them. So JWST will always keep itself slightly within the gravity well of the Earth. As NASA puts it, “…station-keeping burns throughout the mission lifetime will always thrust just enough to leave us a little bit shy of the crest. We want Sisyphus to keep rolling this rock up the gentle slope near the top of the hill – we never want it to roll over the crest and get away from him.”

The potential orbits below show how JWST will be “biased” toward the Earth in its orbit around L2. See also the image above, showing that a slanted orbit can be slanted in more than one way.

OrbitDeterminationAnalysis.jpg

[swood1000]

At 2 p.m. EST today JWST successfully entered orbit around L2 by firing its onboard thrusters for five minutes, adding 3.6 miles per hour to its speed. The first mid-course correction, a 65-minute burn, had added 45 mph and the second, on Dec. 27, had added 6.3 mph. According to Bill Ochs, the JWST project manager, because of the super-precise Arianespace Ariane 5 launch they have been able to save enough fuel on these subsequent corrections to extend the life of JWST significantly beyond the ten-year expected lifetime. They now anticipate having about 20 years of propellant.

[PackMan97]

Another interesting thing shown in graphs of JWST’s orbit around L2 is that it will not be directly over L2 but will be slightly closer to the Earth/Sun. The major reason is that JWST will be constantly subject to radiation pressure from the Sun, pushing it outward. Also it will be subject to the gravitation of the outer planets. However, its thrusters have to be on the opposite side of the sunshield from the telescope and instruments so as not to contaminate the cold side with unwanted heat or with rocket exhaust that could condense on the cold optics. If JWST ever had to thrust itself back in toward the Sun it would have to turn around and expose all the instruments to the Sun, frying them. So JWST will always keep itself slightly within the gravity well of the Earth. As NASA puts it, “…station-keeping burns throughout the mission lifetime will always thrust just enough to leave us a little bit shy of the crest. We want Sisyphus to keep rolling this rock up the gentle slope near the top of the hill – we never want it to roll over the crest and get away from him.”

I just love details like that. Thanks!

For those interested, NC Museum of Natrual Sciences is starting "Astronomy Days" today. The will be virtual again and will go through this weekend. There is probably some stuff that will interest anyone who opens this thread.

https://naturalsciences.org/calendar/astronomy-days/

[swood1000]

By the way, out of the original 344 JWST single point failure items, just 49 remain. But according to Mike Menzel, the Mission Systems Engineer, they

… will not be retired for the duration of the mission. These 49 are typical of all missions, things like propulsion tanks, things like that. And of those 49, fifteen are associated with the instruments, which means if any one of them went – such as a filter wheel failing, we would not fail the mission, we would just fail one of the science objectives associated with that.

[DevilHorse]

Saw this on the morning news:

https://www.nbcnews.com/science/spac...-way-rcna13469

Here is the original announcement abstract:

https://www.nature.com/articles/s41586-021-04272-x

Pulsars rotate at a frequency of about 400 Hz [4.0 x 10 ^ +2 Hz] (cycles per second). Our sun (not a solid object) rotates every 25 days (4.6 x 10^-7 Hz) at its equator and every 36 days at its polls. This thing releases a burst of energy every 20 minutes (0.00083 Hz [8.3 x 10^-4 Hz] really slow in comparison). This signal, was seen in the Radio Wave band which can be seen in this diagram on the far right:
IRSpectrum.jpg
The JWST views energy in the Infrared, which on the same side of the frequency spectrum from the visible light, but much lower energies (longer wavelengths).

Pulsars, which (as mentioned above) spin much faster, emit photons that also are of much higher energy too. These photons are of the visible, x-ray, and gamma ray types.

This 'ultra long period Magnetar' seems to be of a new variety not seen before. Magnetar's are neutron stars with huge magnetic fields (and have a very cool name).
Here is a pointer to what a Magnetar is:
https://earthsky.org/space/what-is-a-magnetar/
I remember Magnetar's first being discussed in the late '90s and graced the cover of Scientific American in 2003.
Magnetar.jpg

Larry
DevilHorse

[DevilHorse]

OK, had enough of the JWST?
Although that statement might be a bit premature, let's take a quick look at the next telescope that comes after the James Webb:

It is the LUVOIR - the Large UV/Optical/IR Surveyor
https://asd.gsfc.nasa.gov/luvoir/design/

The design is not quite done, but the picture looks like the JWST on mineral equivalent of steroids.

Larry
DevilHorse

[-jk]

OK, had enough of the JWST?
Although that statement might be a bit premature, let's take a quick look at the next telescope that comes after the James Webb:

It is the LUVOIR - the Large UV/Optical/IR Surveyor
https://asd.gsfc.nasa.gov/luvoir/design/

The design is not quite done, but the picture looks like the JWST on mineral equivalent of steroids.

Larry
DevilHorse

Looks cool! Will this one take 30 years to get off the ground?

-jk

[DevilHorse]

Looks cool! Will this one take 30 years to get off the ground?

-jk

This one is on the 29 year plan!!

Larry
DevilHorse