Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_30_second_exp_2_winners.thumb.jpg.b5430b40547c40d344fd4493776ab99f.jpg

Recommended Posts

The Crescent Nebula NGC 6888

The Crescent Nebula rides on the Swan’s neck in Cygnus in a dense swathe of Milky Way stars - an ideal target for my first bi-colour image with my new Astrodon 3nm Ha and OIII filters and Esprit 150 telescope.

The nebula was discovered by William Herschel on 15th September, 1792 and he described it as ‘A double star of the 8th magnitude with a faint south preceding milky ray joining to it.8’ long by 1.5’ broad’. This double star is not the prominent star with an apparent companion close to the heart of the nebula, rather, it is ADS13515 at the 2 o’clock position on the nebula’s bright periphery. The bright star off-centre of the nebula is particularly significant as this is the star that is powering the emissions from the surrounding gas cloud. This magnitude +7.5 star, HD192163, is of the Wolf-Rayet type and is also designated WR-136.

Charles Wolf and Georges Rayet first described wolf-Rayet stars in 1867 following detection of their broad emission lines. The Wolf-Rayet stage applies to stars with an original mass in excess of 30 times our own Sun’s mass. This stage comes late in the star's evolution when a rapidly expanding shell of hot gas is powered outwards by the stellar wind only to collide with the much slower-moving gas clouds that were ejected thousands of years previously when the star entered its Red Giant phase. These forceful collisions produce a shock wave that generates an enormous amount of energy including wavelengths within the light spectrum, allowing us to observe them. This complex process displays as an arc of bright nebulosity that we identify as the Crescent Nebula. Long exposure images fill in this arc producing a crab-shell shaped nebulous region rich in Hydrogen Alpha and doubly ionised Oxygen emissions. WR-136 is fated to go supernova at some time in the future – watch this space!

Image Stats

Mount: Mesu 200
Telescope: Sky-Watcher Esprit 150 ED Pro
CCD Camera: QSI 683 WSG-8
Sampling: 1.04”/pixel
Guiding: OAG/LodeStar
Filters: Astrodon 3nm Ha and 3nm OIII
Exposure: 30 x 1800 sec Ha, 15 x 1800 sec OIII
Date: 11/06/17 + 19/06/17 – much of which was under Lunar illumination
Calibration: Bias, Darks & Flats

Object Stats

RA: 20° 12’ 04.6”
Dec: 38° 30’ 46.0”
Magnitude: +10.0
Distance: 4700 light years

The Crescent Nebula – NGC 6888

Crescent_Ha_OIII_OIII.thumb.png.afecae7197a675045f6332c1c0dc0564.png

Comparison of Ha and OIII data

We imagers (well me anyway!) tend to think that Ha is the all-powerful emission line in nebulous objects but it is interesting to compare the Ha and OIII data for this structure as there is an enormous amount of OIII emission present in The Crescent Nebula.

594a60af51197_CrescentHaOIIIcomparison.thumb.png.84648fdf7bd8c4bbc248d9d99e52df98.png

  • Like 26

Share this post


Link to post
Share on other sites

Love the way the [OIII] emission looks like it's wrapping around the HII.

I may have a look at this in [NII].

  • Like 2

Share this post


Link to post
Share on other sites

That's a beauty! Lovely clean OIII data you have there Steve, the Astrodon has done you proud!

  • Like 1

Share this post


Link to post
Share on other sites
2 hours ago, DaveS said:

I may have a look at this in [NII].

The 3nm Ha filter does block this emission which is why some imagers choose the 5nm version but as I already have a 7nm Ha filter, I can continue to use this when imaging planetary nebulae which often benefit from the NII content.

Share this post


Link to post
Share on other sites

This looks great and I love the comparisons as well. I did similar with the Crescent and it was such a surprise as we are normally used to seeing target with next to no OIII! It's a difficult image to balance as well.... nice one Steve :)

  • Like 1

Share this post


Link to post
Share on other sites
1 hour ago, Tyson M said:

Incredible!   Well presented too. 

Couldn't agree more.  Tights stars and sharp Crescent with its filamentary detail without being forced; well defined OIII envelope. Great :icon_salut:.

Very interesting to see the comparison especially for new imagers to help them gauge data for new targets.

  • Like 1

Share this post


Link to post
Share on other sites

that must be the best outer shell i have ever seen it stands out well but still very subtle :shocked: 

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for your comments, folks - it is always very useful to get some feedback and I appreciate you taking the time.

Share this post


Link to post
Share on other sites

Super. The Wolf Rayets do often produce strong OIII emission and OIII envelopes are a treat to image since they don't just enhance an image, they change it entirely. There is an under-imaged OIII shell around the Jellyfish, for instance.

Great job here, Steve, with everything in place.

Olly

  • Like 1

Share this post


Link to post
Share on other sites

Great image Steve! - the Esprit 150 seems to be performing very well!- regards Tony

  • Like 1

Share this post


Link to post
Share on other sites
On 22/06/2017 at 20:46, ollypenrice said:

The Wolf Rayets do often produce strong OIII emission and OIII envelopes are a treat to image since they don't just enhance an image, they change it entirely.

The extreme velocity stellar winds from these W-R stars are amazing, almost hard to imagine the intensity and the effect is shown here in the OIII generation. As for changing the image entirely, I agree and I hope that the two mono images show this well - the Ha version is how I normally visualise this object but the OIII displays a very different beast and a somewhat extended shape.

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By mikemabel
      These are my last images of 2019 taken with my ED72 and 183mm pro to be replaced by a 533pro
      These targets are not easy due to location trees etc except M1 , there was a bright moon as well so are all lucky shots
      but at last i have taken them warts and all . My guiding was all off as well
      Anyway a merry Christmas to you all and a Happy new year 
       
       



    • By codeman
      IC4604 in LRGB Filters. Taking for Namibia during my visit in June 2019. This beautiful nebula is part of the rho Ophiuchi colorful cloud, i the center a 3 blue bright stars the reflect the blue light on the nebula.
      Photo Details:
      Lum - 20 x 5min = 100min
      RGB - 5x5min for each channel at BIN2, 75min
      Total Exposure: 175Min (~3 Hours)
      Telescope: ASA 12'' F3.6
      Mount: DDM 85 Unguided
      Camera: FLI 16200 Mono
      Filters: Astrodon
      Thanks for watching,
      Haim
      My Flicker Page: https://www.flickr.com/photos/101543943@N04/

        

    • By mikemabel
      My first image of M76 A bit rushed as clear nights are a rarity now
      30x120s Bin 2 Luminance ,SW 102 , ZWO 183MM Pro , OVL field flattener ,guided , processed in Gimp
      Took some Ha as well but poor results for some reason
      Seems an Oiii filter may have brought out some more detail
       
      i know its not great but just chuffed to have imaged it
       
       
       
       
       


    • By MartinB
      This has been a bit of a project.  Last year I worked out that my 200mm Canon F2.8 lens and ASI1600 would frame the whole of the Veil complex quite nicely.  I captured Ha and OIII data for the east and west nebulae with a Tak FSQ 106 and added this into the widefield image.  Although the Tak data had to be shrunk down it did add a bit of extra resolution where it was needed.  
      The difficulty for me has been the processing.  I have found it really difficult to tease out the faint wisps of detail and have tried the usual routines of micro contrast adjustments using curves along with Scott Rosen's Screen blend/mask inversion method but the results weren't great owing to the close proximity of faint and bright nebulosity.  I'd heard about the PI process tool for removing stars, Starnet, so loaded this and had a rare foray into PI.  This proved very helpful.  It was a luminence created from Ha and OIII using the 200mm lens with the Tak data mixed in.  Then the starless layer was added in PS with the screen blend mode at 50% opacity.  The nebulosity detail was so well preserved I didn't need a mask.  After blending I reduced the stars a bit more using the starless layer again and darken as the blend at 50%.  I should really unleash some of the stars to add a bit of "punch" but I've wrestled with this data enough for now!  I plan to use it further as I look deeper into the Gorgon that is PixInsight!
      Telescope: Tak 106 for E and W veils.  Canon 200mmL lens
      Camera: ZWO ASI 1600 pro mono cmos, Gain 150, offset 50
      Filters: Baader 7nm OIII and Ha
      E+W Veil 10x30 mins each channel for each nebula.  Whole complex 50x5mins for each channel
      Captured with SGP, calibrated, aligned and combined with PI, processed mainly with PS but PI for Starnet.  Ha mapped to red and OIII to both blue and green

       
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.