Dave's Astronomy    News Posting: 2017-09-01
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2017 Pictures
The Comet and a Supernova
2017-09-01

These are the pictures so far from 2017 and yes as the title says, it includes not only a comet but a supernova as well. And not just any old supernova either, this one's in another galaxy! But the title's still just sort of a teaser because we will lead off this season's photos with a regular galaxy image instead:

M106 - Galaxy in Canes Venatici
This is the galaxy M106 (also known as NGC 4258). M106 is an intermediate spiral galaxy and is located in the Canes Venatici onstellation.

This galaxy was surprisingly easy to photograph from the city. Normally face-on or nearly face-on galaxies are quite dim compared to the local light pollution. However M106 seems to be quite bright even though its apparent magnitude is only listed as 9.1. It also frames well in the MN190 telescope and the reddish coloration works well with the spectral response of the sensor in the STF-8300M camera.

Besides having a well defined core, this galaxy also has a fairly large halo surrounding it. The halo does not show up that well in this image. But it is still faintly visible and I think that if I were to photograph it from a proper dark site it could be more prominent.

Just above M106 and a bit to the left is another galaxy, NGC 4248. And for those with a keen eye, above NGC 4248 are two more galaxies NGC 4231 (left) and NGC 4232 (right) near the top edge of the image. Besides these three, there are a few more small faint galaxies in this image as well.


So that's the season starter image and now here's one of our two headliners: Comet Johnson (C/2015 V2)

This is the first comet image I have ever taken and am pretty happy with the result. Its not perfect though. The core looks oblong and has a dark band in it. I believe this is a result of "trailing" that occurred because of the long (2hr+) exposure. The trailing occurred because I set the telescope to track the background stars and the comet moved a bit relative to the stars during the exposure period.

Experienced comet imagers typically track the comet itself and let the stars trail instead. This would result in a more normal looking round comet core. But like I said, this is my first comet and I used deep sky imaging techniques. So the stars came out quite nice but the comet trailed instead. Oh well, as a first try on a comet it still looks pretty good though.



And then we come to our other headliner for this season, yes its the supernova (SN 2017eaw).

In May of 2017 I took delivery of a new mount, a 10Micron HPS GM1000. This is a very nice mount indeed and I wanted it for mobile, high precision imaging. Once I received the mount, I needed to do testing and learning.

Now, at the time I did this, it just so happened that the galaxy NGC 6946 and the cluster NGC 6939 were in a good position. So, I used them as a test target. Not a bad choice since I had stars, a cluster and a galaxy all in the same field. Little did I know that three days later a supernova would go off in that galaxy.

So the supernova did in fact occur on or about May 14, 2017. But I didn't learn about it until nearly two weeks later when I spotted a post in a popular forum (Cloudy Nights). It seems that a gent who is more on the ball than I learned about the supernova and imaged it a few days after. He also had in his photo archives an old photo of the galaxy he took long before the supernova went off. Using his two photos he did a very good posting that showed the before and after images.

Once I saw that post, I realized I had a really lucky image here and added a post of my own. Mine showed a crop image of the galaxy a mere three nights or so before the discovery. It did indeed show there was no supernova at that point. Then I followed up a few days later and took another image that showed the new supernova.

These three images show the before, after and located supernova:


May 10, 2017,
About 3 days before the supernova

May 27, 2017,
About 14 days after the supernova

And this image indicates which "star" is the supernova.

Indeed, not really that spectacular but consider, it's in another galaxy so its really, and I mean really far away. Yet from here on Earth it looks as bright as any star in our own galaxy. So from close up… wow!

And so what is a supernova anyway you might ask? Well, it’s a star that has reached the end of its life, which caused it to collapse on itself then explode. This page is too short to go into all the physics involved in the death of a star and the resulting supernova. But I will add that this only happens to a small fraction of stars and they need to be very huge (as compared to our sun anyway).

Lastly, you might ask, why is this galaxy called the Fireworks Galaxy anyway? Well, it has a record number of observed supernove in it and as we can see, they go off like fireworks.


Before we move on, a bit of an explanation about these images. First, they are gritty and off color. The gritty look is due to the short exposure times, moonlight and light pollution. I didn't treat these as pretty pictures. The first was simply a test image and the second was only to record the supernova. So the quality isn't there but the supernova is.

The color issue is due to the first image being taken under almost full moonlight. The second was on a darker night so the image came out redder but is clearly different than the first. These differences caused really odd color balance issues and I couldn't get them to match. So I just left them as-is and hope nobody notices... ok hope that nobody cares then.

The last issue with these images is that they are very small crops from much larger images. If you click on the detail page in the above link you will see the entire field of view. Yes, its much larger so when we zoom this closely things get a bit pixellated. Such is the nature of the business when showing a supernova is more important than showing a pretty picture.

And this brings us to the last image of the season. This is the Crescent Nebula, a famous emission nebula in the constellation Cygnus. It's located near the star Sadr and is in one of my favorite areas of the sky to view visually.

The nebula is quite faint and I've never actually seen it from my back yard in the city. But the brighter portion is apparently visible from a dark site and when seen in a large telescope it forms a crescent shape, hence the name.

The nebula mostly glows in the H-alpha wavelengths but I've seen images that reveal other wavelengths as well. The billowing red clouds surrounding the nebula are hydrogen clouds that also emit Ha light.

And thats it so far for 2017. The new mount is working great, the scopes all do their stuff and the sky is outstanding as always. Stay tuned for more once the fall and winter images start rolling in.


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