NGC 6888 - The Crescent Nebula with a guest!

Updated: Apr 28

The Crescent Nebula, also sometimes called the Euro Sign Nebula, is an emission nebula located in the constellation of the Swan, Cygnus, about 4,700 light-years away. It is best photographed in the Summer and Fall Seasons.


NGC 6888 taken by the Hubble Space Telescope

The image on the left was taken by the Hubble Space Telescope in the year 2000.


The HST has only imaged a very small part of the nebula, and we hope it will one day complete an entire mosaic of this incredibly detailed deep sky object!


Why did NASA decide to photograph this particular area of the Crescent Nebula? Because of the Wolf-Rayet 136 star visible in red behind the gases. This massive star is nearing the end of its life and is currently impacting all the surrounding gas with its strong stellar winds. Scientists believe this star will go into supernova rather "soon", in the next million year or so... so look up!




We had never attempted to photograph the Crescent Nebula before. To be honest, we were never really a fan of its shape and didn't really want to image it for that reason. The thing looks like a brain. We changed our mind after seeing a couple of APOD images of the Crescent Nebula where tons and tons of fain gas were visible in the background. Because we now own a monochrome camera and can image in narrowband, we decided to give the Crescent a go!


Another challenge we wanted to take on is the capture of the Soap Bubble Nebula. Have you seen our video about the Top 5 Discoveries by Amateur Astrophotographers?

One of the objects on the list is Ju 1, a very faint nebula made of Hydrogen Alpha that is very difficult to reveal in photography.


The Soap Bubble Nebula

We weren't able to spend a lot of time on this target because of the rising moon, but we did our very best and managed to get the Soap Bubble!


The framing was a little bit difficult and we struggled for about 20 minutes to find the perfect angle so that we could include both NGC 6888 and Ju 1.


You can see a cropped version of the object on the right side, taken directly from our main picture.

Try to find this little bubble in the full image below!


We were hoping to spend more than three hours on it, but did not want to pollute our frames when the moon was up and shining really bright in the sky. We kept all our raw files so that we could add more data to it if we ever revisit this magnificent part of the sky.


NGC 6888 in bi-color with the ASI 1600MM


GEAR USED:

Camera: ZWO ASI 1600mm Pro Mono

Telescope: Orion 8" Astrograph f/3.9

Mount: Atlas EQ-G motorized Mount

Guiding: ZWO ASI 290MM Mini

Acquisition: ZWO ASIAIR

Power: Pegasus Astro Pocket Powerbox

Processing: Pixinsight

ACQUISITION DETAILS:

Total Exposure Time: 3 hours

Exposure Time per frame: 3 minutes

Filters: Ha (1 hour and 30 min) / OIII ((1 hour and 30 min)

Gain: 139


Want to hang this photo in your home? Check out our prints!

How to find the Crescent Nebula?

NGC 6888 cannot be seen with the naked eye. It has a magnitude of 7.4, which isn't that dim, but it is mostly made of Hydrogen Alpha gas which is very difficult to see without filters.

A 10”+ telescope with a wide field eyepiece is recommended to see the gases shaping the Crescent Nebula.

The Crescent nebula can be found in the constellation Cygnus, between the middle star, Sadr, and the star at the base of the swan’s neck. If you plan to attempt to observe this target, be sure to look for it from a very dark location.


Cool Facts

Single Shot & Processing of NGC 6888

This was our second time doing bi-color imaging. We decided to use our Hydrogen Alpha and our Oxygen III filters, and skip on using the Sulfur II filter as it didn't seem like there was any Sulfur gas around the Crescent Nebula. We are pretty pleased with the result overall.


When combining the two channels, we weren't sure which one to pick between an RGB style combination (left) and the Hubble Palette style (right). We ended up picking the Hubble Palette style combination to see more of the Soap Bubble Nebula, but we plan on also processing the RGB style version soon!


You can get our full PixInsight workflow as a PDF "follow along" file HERE.



Below is an invert mask used during our processing workflow on PixInsight. We decided to include it in this post as it can reveal some more detail in the frame, including the Soap Bubble Nebula.


It is still difficult to spot. mostly because it is a ball of hydrogen gas located just in front of lots of Hydrogen Alpha clouds, but it still pops out enough to be seen, especially when the image is inverted.


Were you able to spot it on the picture above?


If not ,here is a crop on Ju 1, inverted. You can really see it much easier now.

Although small, the Soap Bubble Nebula is really beautiful looking as it looks very smooth and round.


The discovery of Ju 1 was made by Dave Jurasevich, an amateur astrophotographer, just like you and us. Dave was using his 160 mm refractor f/7.7 and a 6nm Hydrogen Alpha filter when he spotted the object during processing.



How much data can you get with each filter?


As you may know, we love to show you guys what the stacked data for each channel looks like before combining it into a color image. That way, you can see and compare how much data each filter can reveal when used for deep sky imaging.


Below is our stacked image of one and a half hour each for Hydrogen Alpha and Oxygen III.



Final Thoughts

We never thought we'd love NGC 6888 so much! We were never interested in imaging this target, but having the challenge of capturing the faint Ha gas in the background as well as the tiny Soap Bubble Nebula really helped us fall in love with this part of the sky.


We definitely recommend you try this target with your own equipment. If you do not own a Hydrogen Alpha filter for your monochrome or DSLR camera, maybe start by photographing the Crescent alone and leave Ju 1 for another time. That way you can center NGC 6888 in the middle of your frame and would only have to worry about it for now!


If you plan on going for the Soap Bubble as well, do your best to spend as many hours as possible on it. As you can see, three hours is enough if imaging far from the city, but you'll definitely have a more impressive image if you spend more time overall.


Add your image of the Crescent Nebula and/or the Soap Bubble Nebula in the comments! We'd all love to see your work :)


Want to hang this photo in your home? Check out our prints!


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Clear Skies,

Galactic Hunter





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