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welcome to hubble's universe unfiltered

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the year 2015 was the 25th anniversary

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of the launch of the hubble space

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telescope

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and every year for the anniversary we

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produce a special image to celebrate

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now it's kind of hard after all the

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amazing images that hubble has produced

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to find one image that's more

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spectacular than all the others

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however for the 25th anniversary we

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wanted to do something special so we

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made it stand out in a different way

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let me orient you

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toward the target

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this video

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starts in the karina constellation which

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features the wonderful karina nebula

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that hubble has looked at many times but

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that's not the target there are several

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smaller nebula to its right

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and this nebula is the target it's

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called gum29

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this is a ground-based image of the

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nebula gum29 and you can see it consists

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of a star cluster and its associated gas

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the ultraviolet light from the stars is

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heating the gas and causing it to glow

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however if we look in infrared light

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this is an image from the spitzer space

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telescope

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we can see that the gas is actually

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warmed over a much larger region than we

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see in visible light we zoom in towards

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the center of the star cluster and

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nasa's other great observatory the

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chandra x-ray telescope took this image

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of the star cluster

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and you can see the copious amounts of

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x-rays coming from that star cluster

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which indicates these must be very

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massive stars

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getting a lot of x-rays indicates you've

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got a really massive star cluster here

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so

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looking at those images gave us optimism

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that this was going to be a really cool

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image from hubble

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so here is the field of view in the

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spitzer image that hubble viewed with

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visible light

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and hubble

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has much better resolution than spitzer

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so this was the release image of the

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nebula gum 29 and the star cluster

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westerlund 2 at its core

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and the resolution is even better than

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i'm showing you here because this image

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is about 9 000 pixels across

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so if i zoom into that star cluster you

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can see it breaks up into an amazing

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number of stars there are several

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thousand massive bright stars in this

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cluster

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if i look along the nebula wall we see a

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whole range of these pillars we've seen

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lots of pillars with hubble well here we

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have several of them all in one region

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along the wall of the nebula of gum29

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we also have one of these pillars bathed

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in sort of this purple glow and so

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there's a lot of cool details in this

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image

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and hubble was able to get a really

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wonderfully high resolution and all

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sorts of interesting details

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now to make it special

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i work in the visualization group and

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they asked us to take this and take this

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2d image and pull it out into 3d

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to remind you that these aren't 2d

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picture postcards of the night sky

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they're really representations of a

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three-dimensional universe

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well to do that visualization we

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recognize that this press release image

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was actually part of a slightly larger

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region this was the full image that we

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took with hubble and we cropped down to

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that for the press release image

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and we're going to take that full image

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and place it on top of the ground-based

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image to give you context

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now when we do a visualization we want a

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widescreen aspect ratio

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so we cropped it down to the widescreen

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aspect ratio we blended the hubble image

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and the background image together and

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this was our starting point for our

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visualization

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now we want to take a look at that

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nebula but you've got all these stars in

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the way so the first thing we do is boom

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get rid of all the stars

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now i love giving talks and being able

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to go one slide to the next and having

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all those stars disappear but of course

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you should recognize that's a tremendous

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amount of work by our visualization team

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and of course once we get rid of those

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stars we have to bring them back in

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for this we developed a new technique of

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a point spread function stars now let me

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explain what that is

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so

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when hubble observes a star that star is

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just a point of light and the brighter

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stars get bigger on hubble's detectors

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and they spread out

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so we characterize very carefully

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how a point spreads out on hubble's

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detectors we call that the point spread

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function

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we astronomers are pretty straight

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forward to what we call things

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here is an example of one of hubble's

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point spread functions so you can see in

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the upper left it's just a dot and as

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you come towards the

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across

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and down it gets brighter and brighter

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and the star gets bigger and also

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develops these diff diffraction spikes

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this is what a star looks like in one of

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hubble's detectors as one gets brighter

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and brighter stars

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knowing that we can go in

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and examine the hubble image

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and characterize those stars

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so we did it in three different filters

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one that will be red one that'll be

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green and one that will be blue

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we measured the positions of all those

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stars and their brightnesses in the

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three different filters

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and then using the point spread function

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we could recreate those stars

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artificially well i don't wanna say

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artificially more synthetically we can

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create them digitally without you know

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going into the image and cutting out

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little postage straps around each star

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we could go in and create them digitally

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furthermore you may notice that the

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stars of the cluster are significantly

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redder than the other stars

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that helps us pull out the stars in the

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cluster and separate it from the stars

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in the foreground

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we do that with what astronomers call a

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color color diagram

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and basically it's just a way of

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separating which stars are redder or

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bluer than the others

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and in the left-hand panel you can see

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that white line well those are the

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foreground stars and the red clump well

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those are the stars we identified as

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being part of the cluster

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here in the middle panel we've got all

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the stars together with the cluster

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stars colored red and in the right panel

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we have the foreground stars using this

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color color diagram enabled us to do a

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pretty good separation between the stars

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of the cluster and the stars in the

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foreground you can see it wasn't a

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perfect separation there's a little over

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density in the foreground stars but for

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the purposes of this visualization it's

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quite sufficient

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so here are the stars of the cluster

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and the foreground stars all created

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synthetically using point spread

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functions

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now you'll notice there are empty spaces

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on either side where we blend it into

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the ground-based image

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to do that we had to go to another

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catalog from the 2-mass survey

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and we gathered stars from a wide region

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around this area and then identified

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those that were in our field of view but

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not inside the hubble part of the image

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this is an infrared catalog so we had to

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take the band passes in infrared map

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them to the hubble band passes and

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adjust the magnitudes appropriately to

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get the proper colors

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again we use the hubble psf

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and we ended up being able to fill in

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the stars on the outer part of the field

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altogether

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here are all the stars done with this

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point spread function technique

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now we've got to deal with the nebula

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itself and the nebula has several parts

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you can see here's the foreground gas on

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the near side of the nebula here are all

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these pillars along the inner edge of

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the nebula and then we've got that

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bright gas in the background part of the

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nebula

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each of those is going to be a separate

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layer inside the nebula and we're going

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to do it with a technique we call

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sculpted decoupage

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let me explain a little bit

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here is

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an image called the great wave of canada

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and it has several layers in it you can

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see that you've got the wave in the

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foreground you've got the mountains in

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the background

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and if you take that image multiple

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times and slice it up into the various

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pieces

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together with little separators in them

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you can create what's called a decoupage

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box here is an actual decoupage box and

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here are views of it

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from different angles showing how you

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get a 3d technique by simply putting in

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multiple layers of the same image

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well we're going to do the same sort of

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thing digitally

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but we're also not going to use just

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flat layers we're going to sculpt each

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of those layers

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so for example these are the layers in

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our digital model that represent the

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background of the nebula and you see how

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they have sort of a bowl shape because

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that's how the background part of the

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nebula would look

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here are the layers that represent the

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pillars

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and you'll notice that one of them is

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tilted because we want to make sure all

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of those pillars point towards the star

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cluster because it is the energetic

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radiation from the star cluster that is

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creating those pillars all those pillars

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point in 3d towards that star cluster

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here are the layers that are on the

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foreground of the nebula

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and finally we have a layer just in

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front of the nebula called the veil

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which is a layer of thin gas that sort

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of forms a bubble along the front of the

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nebula add to that the cluster stars

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as well as the foreground stars from

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hubble

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and then the foreground stars from the

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surrounding region

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together you get the full

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3d model that we use for our

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visualization

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looks kind of like a christmas tree

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of course this is a side view of it and

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the camera would actually be located at

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the top of the tree

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here is a movie showing you a build up

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from back to front

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we start with the background layers of

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the nebula

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the brighter gas add in the cluster

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stars and then all of those individual

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little pillars along the inner edge of

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the nebula

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then we start with several layers for

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the foreground

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add in the veil layers and finally add

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in the stars

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now we have ourselves a full

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three-dimensional model and we can

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we called that visualization celestial

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fireworks both for the large number of

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very bright stars in that cluster as

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well as for the celebration of hubble's

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25th anniversary

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i thought it was a fitting addition to

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an amazing panoply of hubble's imagery

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thank you for watching we'll see you