Why are JWST Stars so SPIKY?! | Diffraction Spikes Explained
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- Опубликовано: 29 сен 2024
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NASA Press Release on the Image: www.nasa.gov/p...
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MORE INFO ON DIFFRACTION:
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JWST Technical report: www.stsci.edu/...
Diffraction Spike Wikipedia page: en.wikipedia.o...
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Small clarification: At around 2:33, I said "each edge of Webb's mirror produces one diffraction spike in the image". It would have been clearer to say that each edge produce two spikes in the direction perpendicular to the edge - it's just like the struts we discuss later in the video. For example, one edge would contribute to spikes 2 and 5 (as they are labelled at 2:11), and the edge opposite contributes to the same spikes and makes them brighter. Hope this clears that up!
But would the spikes obscure the images of the planets circling the star
Should have installed spinning struts.
I am God himself and I say you are right about the edges of the mirror and also you won't find life on Alpha centuri You will find it in one of its next planets satelites. Also an humble request to all of you space explorars please stop looking inside my underwear with infrared telescopes ask me things directly next time till then peace...!!!!😇😂
Damn straight. I’m getting so paranoid about them looking in my undies that I had to stop wearing them. But summer is coming so I should be OK.
Even after Hubble was repaired it tool them some time to dial it in and when they did it was breath taking. They are easy to process out with out losing to much resolution is just a question run time.
Its the planets around the stars that matter I would not be surprise to hear the news that a planet with artificial light coming from has been discovered.
Every object in that image has the same set of diffraction spikes present. The reason you notice it for the target star is because it's extremely overexposed relative to the rest of the field. If you adjusted the exposure to make the target star appear normal, you wouldn't see most of the other details. If you want to see faint spikes around some of the other stars, look up the original image on the NASA site.
Exactly! The spikes represent some small percentage of the light of the object, and since this one is so bright to Webb the spikes look huge, for the fainter objects in the background the spikes are much smaller.
@Amilton Sánchez The link I posted got blocked or deleted, but you can find it if you google the terms "nasa telescope alignment evaluation image".
@@ChrisPattisonCosmo that’s really reassuring actually 😅
It still would be better if it was one big homogeneous mirror and no struts to minimize diffraction. That would be impossible to do i don't ask for the impossible.
Go watch the stage lights of Michael Jackson live in Bucharest. Notice how they specifically only make hexagrams and only at random moments. But they are perfect looking hexagrams. These patterns correspond to the star of David or star of life or flower of life patterns. Cameras are based off the eyes. The first camera was the camera obscura.
Thanks so much for answering the question that's popping into my head everytime they show an updated image. The diffraction is so distracting I was thinking it was a flaw in the telescope. You're video is the first I've come across to address this question. I'm an instant fan. Thanks again!
Thanks so much, and I'm glad it helped :)
Your*
@@instamdgram Your right. Thanks four policing my typos.
@@EverythingYouKnowIsWrong lol, was that "four" intentional after that 😆?
By turning the telescope and taking another picture, you can retrieve that information and overlay it on the original picture, to get the whole image without the spikes. You erase the spikes on each photo or many photos. Using a different picture to replace the parts you erased. But it is easy to just turn the telescope to a point where the spikes don't interfere with what you want to study. So no problem.
You are a genius.
But it's more complicated than just removing it by sophisticated postprocessing. I think that it would be relatively easy, because the spikes are just function of size and brightness and exposition. Anyway, for some specific targets with details around the stars (nebulas or even planets) it might be better solution to rotate the telescope by e.g. 15 degrees just by using gyros.
im pretty sure rolling the JWST to get two photos where the spikes dont overlap is impossible for most targets, since one side must always face the sun, and the Mirror is fixed in place. So the only way to get images where the spikes dont overlap is to take shots about a month apart, and in roughly polar direction. For stuff in equatorial direction the spikes will pretty much always overlap, unlesss you rotate the telescope in such a way that the mirror gets exposed to sunlight...
The lines you mention at 5:40 may be due to phase shifts between the light bouncing from different mirrors at not equal depths (maybe small as a wavelength fraction) and so producing phase addition and substraction (cancellation). I guess. This procedure of mirror phase alignment, I heard that the telescope can perform due to the mirrors actuators, but at the time that this photograph was taken, the mirrors I believe were not yet adjusted phase-wise.
Oh that's interesting, thanks!
Congrats on getting so many views!
Thanks, it completely surprised me! :)
Why aren't the spikes removed from the final image with software?
They just don't need to here. This is just a calibration image, not for science, and the exact shape and resolution of the spikes tells us about the calibration of the mirror. Plus the spikes look cool, which is good for an image like this which is released to the public!
@@ChrisPattisonCosmo Thanks.
They are there because, Mr. Webb forgot to remove his Bahtinov mask. Duh... smileyface
Doh!
The reason for several slightly disaligned spikes are that these are position dependent over the CCD. As you may notice, this image is not a single frame, but a coadd of several individual exposures with different pointings. As you put the star across the CCD the spikes are slightly different, creating this effect in this coadd image
From the previous alignment images, I get the impression the JWST team was using the shape of the diffraction spikes as an indication of how good the alignment is. Is that correct?
I believe so!
I "think" that they were using the diffraction spikes specifically to align the mirrors together.
Basically move one mirror at a time, until all the compound images of the star are on top of each other, and then use the diffraction spikes to further tweak, keep tweaking them one by one until all the spikes are overlaid on each other.
I suspect that the multi-line effect in the diffraction spikes, means there's still room to further tweak the alignment (it may be at it's aligning limit though, I dunno). The fact that there are previously never seen galaxies in the background is a sign that it's going to add a lot to our telescope capabilities. I mean some of those, you can clearly see the shape of the galaxies, and those weren't even a blob or a spec in hubble's eye.
The spikes can be minimized by exotic software in post processing, but a lot of types of research won't need this extra step. I've done some noise-minimizing in regular low light/high ISO photography, by having a camera take 2 images in rapid succession, one with a closed aperture, and using the black image as a "noise map", to help identify & remove noise from the open aperture image. But that doesn't remove spikes. NASA has much more fancy software solutions than this though ;)
Excellent detailed presentation.
But some of the smaller stars have diffraction spikes that are in directions 30 degrees away from those of the main central star.
I notice that the overall shape of the complete main mirror is hexagonal but rotated 30 degrees from the individual hexagonal elements. Is this connected to the above effect?
Confusing!
Just a silly question: knowing the origin of those spikes, why cant we compute back the (spike) photons to their "real" location and thus get an undisturbed image?
they can, but as he said in the end of the vid this picture was just for engineering purposes only.
one of those purposes is testing their abilities to do exactly what you suggested.
Of COURSE they can! It's a totally digital image; NOTHING is in there that they don't WANT to be in there. If you'll notice, not ALL stars have it, so it's NOT caused by anything they can't fix. The popular "Cross Star" filters for film cameras led to the idea, I'm sure. Yeah, they could clean them up, and likely will at some point and claim a success over the 'problem' they finally fixed.
What I'm really astonished by is how, in spite of being zoomed in on that one single star, you can very clearly distinguish infrared light sources from MANY, MANY, stars in the background that aren't in focus but still have very vivid clarity
Quit looking directly at the sun!! Same thing with the JWST--don't point it to a nearby star; that's not what it was built for!
I've definitely been wondering what causes those spikes. Thanks for making such a clear video about it :)
I get diffraction spikes in my vision all the time.
I can see those when my eyes are tired and I look at a street light or something
Wonderfully explained, thank you so much! :)
After the release of the 5 images by Webb, I must say the diffraction spikes are something so pretty that I don't mind them at all ;) They add this 'starry' effect ;) I like them! :)
Just found your channel. I like the way you present your content. I subscribed and look forward to your future videos. It is an exciting time to be a human 🚀
Thanks so much! The next few years will be very exciting for astronomy - a lot of amazing telescopes are coming online soon!🤩
Just a slight point: the struts on Webb are not at 120 degree hence their diffraction pattern wouldn't be as you show at 5:18 ie 6 equally spaced spikes. If they were then they would not line up with the 6 spikes produced by the mirror edges. The two sets of spikes would be offset by 30 degrees. However, I notice from the final image at 5:36 that the spike pattern is exactly that which is seen in the actually photo. I guess this unequal spacing cause both sets of strut patterns to line up - apart from the horizontal pair? (Like your video - thought it was clear and informative.)
This is a really interesting point that I should have mentioned, thanks for pointing it out! I honestly don't know for sure why the struts are like that, but I would guess that you are correct, to overlap some of the spikes and minimise the effect of them. Either that or it could be something to do with the unfolding process or precsion of the mirror, I will try to find out!
@@ChrisPattisonCosmo Thanks for replying Chris. One other thing which makes this issue more complicated than normal is that the exact diffraction pattern produced by the struts is also dependant on where the struts are with relationship to the focal plane of the instrument. All the analysis that I have ever come across assumes that the 'spider' lies in the same plane as the secondary mirror. On the JWST however they are angled from the reflecting mirror plane down towards a plane close to the main mirror. I am unsure how this affects the diffraction pattern (actually that's a lie - I am not unsure - I've no idea) but I am certain it would complicate the issue.
Yep, the struts on Webb were designed to create that line up and fewer diffraction spikes
@@cstockman3461 Thanks.
Thanks! It however raises another question. Why is the sensor supported by a tripod? I understand the structure stability the shape provides but in the absence of any loads upon it in the vacuum of space suggests one arm might have been enough. Are three used primarily to allow the sensor location to be aligned more accurately?
The loads from liftoff, and the precision movements required to focus the lens mandated a stronger arm then a single one.
Each of the arms can move independently so they can fine tune the focus. The tripod also provides stability. with exposure times as long as they use, every bis of stability counts.
There's also the issue of vibrations. Having the secondary mirror as an oscillator at the end of a cantilever strut, while having an oscillating mass in the form of the cryocooler piston on the craft... not good.
@@HotelPapa100 vibrations are so bad that they are close to 0 K on the mirror side of the telescope. and they need it because of the faint rays they want to capture. they are so faint that the heat of the telescope itself would overexpose the image everytime.
There's a bunch of reasons, for example, when the sensors are getting deployed, there's the inertia from the weight of the sensor, which is heavy, having for example just one arm to put that in the correct position would cause flexing in the arms and it wouldn't be positioned exactly where they would've wanted, any orbit maneuver that would be needed would also create vibrations and change the position of the sensors, the design basically needs to be the exact opposite of what mechanical engineers design here on earth, it needs to be very very hard because they need the precision.
Some amateur telescopes use curved secondary vanes. This does not eliminate the spikes; it just smears them out. There are obstruction free reflector designs like the Chiefspiegler, but these are rare and are made in longer f ratios.
The curves vein ones are pretty cool! A refractor telescope doesn't have diffraction spikes from struts (because they have no struts), but they're too heavy to get into space at present
This is also similar to the concept wherein “bokeh” in a photo are tiny representations of the shape of the cameras aperture. This is basically a bokeh shape with diffraction patterns overlaid.
It's spike level is over 9000!!!!
Excellent explanation. So I wasn't the only person concerned with the spikes.
Thanks! Rest assured the spikes won't be so bad when Webb looks at most of its (much fainter) targets :)
JWST has astigmatism
Thank you so much, Chris! One question still lingers in my mind: why exactly is the number of spikes twice the number of sides of the aperture when odd and equal to it when even? I don't quite understand.
Thanks for the great question!
It's because each edge produces two spikes, perpendicular to the edge. For even sided apertures, opposite edges both produce spikes, but they overlap, so the two edges combine to only give two visible spikes. For odd sided shapes, there aren't any opposite sides, so no combining and each edge gives two spikes. Does that make sense?
@@ChrisPattisonCosmo Oh yes, thanks very much!
Thank you Chris for explaining the source of those spikes, to be honest when I first saw that image I was not at all impressed as I was expecting a clear image of a spherical star, not a spikey star.
I wonder why they can't produce clear images without those spikes, I know they'll just say it's the laws of physics/diffraction etc etc but we have supercomputers now which should be able to remove those artefacts surely?
If we know what causes them we should be able to remove them?
I think diffraction will always happen for a reflection telescope like Webb. Refraction telescope don't have the same problem, but are WAY heavier and so putting one in space just isn't feasible yet. They can remove the spikes after the images are taken, but that process also loses some contrast in the rest of the image. For fainter objects (this star is deliberately way too bright here), the diffraction is a much smaller issue and it won't affect the science being done!
@@ChrisPattisonCosmo I miss a viewer like you . I had not even one clever comment in 2 months .
There are certainly scenarios where you would want to remove them, but the process can introduce noise and cause other details to be lost, so depending on the application and the science being done they are not always removed even though we have the capability. Dr. Becky has a good video explaining this.
Nice job, you spiked my interest for sure 😄😂
Ha, thanks!
Lol this was a question for one of my Fourier theory assignments. It's very interesting.
Man i thought the JWST pictures were already TOP NOTCH qualitym, the best possible, but there is still a lot of room for improvement i didnt actually think that wow!
It’s a good thing. It means the telescope is super sensitive. The Star is 100 times too faint to be seen with the naked eye and those spikes and the brilliance of that faint star means the JWST is super sensitive. Let’s look back in time.
My guess is that the star is in our galaxy..just like the hubble when there is a lens flare its because its so close..in our galaxy..
That's right, it is in the Big Dipper constellation, although it's too faint to see with the naked eye, but it's incredibly bright for Webb!
I'd like to know more about the salt based lenses that are used on the telescope
Personally I love diffraction spikes. Especially when they're split spectrum and accompanied with some awesome music.
Was wondering with the analogy of using slit to explain mirror diffraction, the slit experiment usually uses very small slit (on the order of the wavelength), but mirrors are very large. Will they have the same diffraction pattern?
Flat earthers be like “The government is making us believe 6 Spike Stars don’t exist” 🤡🤡🤡
Boring
This was my question. I was supposed to ask my professor regarding this.Thanks for your answer
As an amateur astronomer, I've never been too upset by diffraction spikes...in fact they sometimes add to the enjoyment when viewing visually. (The Pleiades look awesome with diffraction spikes as does Sirius).
The one thought that comes to mind...do the diffraction spikes contain information about the subject star? Obviously there will be chromatic and spectrographic information, but I wonder if the presence of protoplanetary discs or even planets could be extrapolated from the spikes.
Sounds like a good subject for a thesis if there's any astronomy students looking for a doctorate!🤔
That's a super interesting question! I agree the spikes make it look great, I wouldn't want them removed from most photos! I suspect the spikes just wash out information, but maybe someone who knows more than me would be able to retrieve some information from them.
afaik - In the Visible Spectrum you can analyze the Spikes. They have different colors and therefore can tell roughly about the composition of the star.
My vision is not the greatest and I have always wondered what those two, vertical spikes were caused by when I look at lights. I assume it is my eyelids doing this when I squint. Christmas lights do this when I'm not squinting though so I'm not sure.
Exactly the video I was looking for after the recent image release. Thanks!
Couldn't those thin lines within the spikes be produced by the different distances/angles of the mirrors to the sensor? Those would be interference patterns.
Wait till you get cataracts, then you’ll really see diffraction spikes, so much so that it becomes impossible to drive at night.
So in a nutshell ..... diffraction is caused by diffraction ... brilliant anaysis
So basically it is a very advanced version Newton's telescope its hard to fathom just how smart he was and when you understand technology the effect he had on all of us.
I vote to re-name the Star 'ENA'.
Number one in Greek. The first thing we see at the forefront of a greater understanding of the Universe.
Love it!
I learnt diffraction only occurs when the obstacle size is smaller than the lenghtwave. Altho here it seems its not the case? Why does it happen then?
Great show! Optic technology should correct. Why are some spikes much longer, thicker etc, and variate day to day?
I don't accept spikey stars....they should be able to correct for this.
The foreground while magnitudes dimmer had no issues. Sure the focal process some type of filtering is not being used for citing it in.
Really enjoyed this video.. im just amazed that everything has gone to plan .
Thanks! I agree it's incredible (almost unbelieveable) that nothing has gone wrong (yet!)
I see them spikes two house down the block. Lol it reminds me of that everytime I watch videos on jwst.
I wonder if the next telescope after this is going to have eight diffraction spikes. Haha
I very much appreciate the straightforward explanation. Those spiky rays did bother me a bit.
in 70s space movies spiky stars were exactly what we saw. finally the future is here!
Rotation combined with a
filter can improve optics..
Just realized that 2 of the struts are closer to each other exactly because diffraction pattern will be overlaid by the pattern from mirror.
Is this holes in red background 1:07 ghosting effect?
Great explanation, thank you
Thanks! :)
Understand they made a design mistake in james webb telescope
there is a grid in the planet and there is a grid in space those lines you see are the lines of that grid in space, the sun is one of those stars that holds that grid, the light of the star shine those line close to it.
Now that there's a decent mirror in space ... God can have a shave.
The image around 5:35 answers my curiosity with this subject and until I found your video I hadn't even remotely come close to finding that article. Thanks for the great explanation!
Thanks! I'm glad it helped!
3:12
Congratulations for 559 subs
Thank you so much 😀
@@ChrisPattisonCosmo most welcome ☺️
Well, the spikes can simply be mathematically corrected. No issue with them at all.
Are thorn's and spear's and gunshell's a problem?
If you increase the red tone or temp of that image you can see more hidden.
Lens flares-must be a JJ Abrahms picture.
Even the ancients knew of this as it is shown in their petroglyphs.
when will we see aliens?
Hopefully soon!
I have minor astigmatism so I didn’t even notice them 😂
Just photoshop them out. Add a mustache and specs too
"spikey" not spiky; exposure duration
Thanks! I was wondering about that.
This is what i get with my eyes,
At night light makes it look like that
NGL - I'm so tempted to show this video to a group of 'Flat-Earth Union' in my nearby city of Akihabara... so they would finally know what 'diffraction' means 🙄
Please let me know what they say if you do! 🤣
JWST's proposed 8m successor has a strut-less off-centre design: ruclips.net/video/gj0710Ih448/видео.html
Does this eliminate the strut-related contribution to the diffraction?
I think it will reduce the effect, but not remove it entirely. LUVOIR will be incredible if/when it flies!
I'm a retired professional photographer. No matter how much you try to technically explain the "star burst" effect, it's an expensive optical distortion. I'm sure it will be corrected soon via computer jiggery pokery, though I was expecting the JW telescope to do this internally considering its advanced onboard computers.
In this particular image, the star was overexposed, and the light curve is logarithmic, to make the spikes as bright as possible, because there's information on how good the mirror alignment is in those spikes. Science images won't be overexposed or use this light curve.
Question is, did NASA know about the diffraction before sending the telescope into space? If they didn't know about it than the JWS is a disappointment.
They knew, every space telescope and most groubd based telescope have them. It's not an issue for the science Webb will do :)
La longitud de onda es tan pequeña que haría falta una lente mucho mayor para que no se produjera la difracción de la onda.
Spikiness is normal, can't avoid diffraction entirely. But who gives a f*** about that, look at that resolution on those galaxies!!! That are billions of light years away, and it's like taking a photo with an iPhone at 10 feet away. Of course in the infrared instead of the visible spectrum but still, woooow!
Heck yes!
“It won’t affect the science.” Except trying to resolve exoplanets around nearby stars, one of the touted purposes of the dammed thing.
That’s why Webb has coronagraphs
You have to marvel at the technology. If I understand correctly, all 18 mirrors need to be aligned at the nanometer accuracy, smaller than the wavelength of the infrared light it's photographing, in order to get a perfect picture. If they weren't aligned to that accuracy all you would get is, effectively, 18 separate pictures superimposed on top of one another, which is not the same thing as having one single picture with 18 times the accuracy. The 18 pictures might be superimposed almost perfectly, but it would still not be the same. It's only when the mirrors are aligned at nanometer accuracy when they all work as if they were one single gigantic mirror.
Yep, you've got it right, that's a great summary!
What about the smaller versions of the spiky star that show up in the image? There are about 15, of different sizes, some of them with black spots. I'm assuming that they are some other optical artifact, but haven't seen it discussed anywhere. I am also assuming that they won't be a problem for scientific observations, because they only happen because this star was so bright, so saturated. But that's a lot of assumptions.
The smaller objects with spikes are background galaxies that are still bright enough to cause visible diffraction spikes, through exactly the same processes! The black spots are also some optical artifact or compression issue as you say, they are real objects!
Thanks so much from a new subscriber. Those spikes annoyed me, but now I know why they appear, I'm comfortable with them.
Thanks! At least it's always going to be easy to know if a picture came from Webb because they will all have the 6 spikes!
100k views? Damn dude this video blew up. I'll check out the rest of your channel this was a good video
Haha, thanks a lot! :)
The only thing is the two bottom struts are not as wide as the starlight suggests. If you notice they're both near the center, bottom. They're each one hexagon away from the center. The starlight suggests they're much wider spaced at the 4 o'clock position rather than 5 o' clock. Chris Pattison, can you explain this? Thank you
Greeat spot, I should have commented on this in the video. I don't know for certain why this is, but it could be to make sure the diffraction spikes from those stuts overlap exactly with the ones already produced by the mirror shape.
NASA said they used Fourier Series to align the edges of hexagonal mirrors. Can you explain that?
Every mirror (or rather: every edge) creates some diffraction signal that is visible in the picture. Now, there are several mirrors and even more edges in the entire JWST's optical system and when all those combine, in the picture you will see a SUM of all those diffraction patterns. You won't be able to easily discern which individual diffraction signal is where, and which element of optical system created it, simply because they're all mashed together in some way.
That's where Fourier transformation comes into picture (pun entirely intended).
Basically, if you know that a given output signal is in fact a sum of various different periodic signal (think waves of different amplitudes and frequencies combining into a single, large wave) you can very neatly decompose that signal into those EXACT component waves. You can find plenty of pictures that illustrate how it works in the internet.
In this case, you take light visible in the picture (signal), you run it through Fourier transformation and you WILL get all the underlying individual signals (diffraction spikes from every individual element in the optical system). Which obviously helped NASA calibrate the telescope much faster than if they just did trial and error.
How does it work on mathematical level? Magic. No, seriously, it just works. But it involves calculus and literal imaginary numbers, so don't delve too deep into it, that way lies madness.
In addition to the 8 large spikes there are many tiny spikes. Do we know what causes those? If they were all digitally (or theoretically) removed would we have a circular image corresponding to the size of the star?
The star is smaller than a single pixel. You get some leakage into adjacent pixels.
bending of light is refraction
Please slow down your narration.
Maybe someone should make a telescope with a magnetic floating secondary mirror. No struts at all.
That would be amazing, but maybe too heavy for space, or not easy to calibrate to the precision needed? But you might have just invented a telescope of the future!
thanks for this amazing quality videos! my fav channel about JWST related stuff for sure!
Thanks for much!
There is no link to official JWST sites, only your links, where is this image from, please confirm.
Sure, I added a link in the description to the NASA press release on the image. Hope that helps
Perhaps explain the new Magellan Telescope, to be operation in 2029, was designed not to have spikes.
Interesting, that's a great iea, thanks! :)
Angular diffraction = 1.22 * wave length of light / diameter of telescope mirror.
Webb has larger mirror diameter than Hubble, but infrared light has longer wave length, and its resolution is limited by diffraction,
so its resolution in infrared wavelength is not much better than Hubble in visible light wavelength.
You're not wrong! The joy of Webb is that it can see into places that Hubble can't (i.e. through dust and further back in time)
Only in the far infra red. The telescope sees in a very wide spectrum starting from very long infra red through near infra red and even the red end of the visible spectrum (about 30 microns to half a micron). At the shorter end of that range its resolution is significantly better than Hubble is in any of the wavelengths it can see. For example in red light the JWST's resolution is about 2.4 times better than Hubble is in that same wavelength.
The worst case is when comparing JWST at its longest wavelength to what Hubble sees in UV, in which case the situation reverses such that Hubble's resolution is almost 100 times better than JWST.
@@listerdave1240
We don't know whether the JWST is diffraction-limited in the red yet, it's only been tested at 2 microns.
@@IamGrimalkin True. I'm referring to it's design specification, in which it is meant to be diffraction limited even in the red. We will have to wait and see whether it actually achieves that but I have high hopes that it will.
wouldn't it be nice if the secondary mirror could be "mounted" in place by a magnetic "strut" system.
That would be awesome, but very difficult to achieve the required precision I think!
We're getting close now they have everything aligned and ready I think the NASA page says one more thing had to be done and it's ready for science
Yep, just instrument commisioning left to do (takes about 2 months), and then science can begin! :)