When we travel to the fabulous dark skies of Dell City, Texas, I try to pick a combination of challenging targets and targets that I’m confident I’ll get good results with. In October, one of my picks for the “good result” target was M31, the Andromeda Galaxy.
It seemed fitting to image the Andromeda Galaxy now because we are approaching the 100 year anniversary of Dr. Edwin Hubble’s November 23, 1924 New York Times article confirming that some objects classified as nebulae were, in fact, “island universes” – galaxies separate from our own. Hubble used the Cephid variable stars in the Andromeda Galaxy and in M33 to measure the distance to those two galaxies and determine that they had to be outside of our own galaxy – on the order of 1 million light years away. Based on that distance and its apparent size, Hubble calculated that the Andromeda Galaxy’s diameter was 45,000 light years.
100 years later, the Andromeda Galaxy is known to be 2.56 million light years away. Its apparent size is 3.167 degrees by 1 degree, giving it a diameter of 141,000 light years. So even further and even bigger than Hubble calculated!
It is amazing to me that we’ve only understood that there were other galaxies for 100 years! And I think it is cool that we keep learning more and more about the universe around us.
This image of the Andromeda Galaxy was captured using red, green, blue and hydrogen-alpha filters. Although Ha actually is in the red part of the spectrum, it is frequently mapped to purple-pink so it stands out, and I have used that mapping here. These Ha regions are star-forming nebula in the Andromeda Galaxy, similar to our own Orion nebula and Eagle Nebula.
So while Hubble proved that Andromeda was a galaxy and not a nebula … it also contains its own nebulae. And we can see them! How amazing is that?
I have a bunch of wide field comet images from Dell City, Texas and Pearland, Texas that are proving … challenging … to process, given that they were taken near dusk with a DSLR on a tripod. Everything is changing – the Earth is rotating (so the stars are moving relative to the camera on a non-tracking tripod), the comet is moving relative to the stars, and the sky brightness is changing.
But now Comet C/2023 A3 Tsuchinshan Atlas is getting higher in the night sky, so it is no longer visible only at dusk. So I could set up my tracking mount and telescope to image it. The tail is still really long – much longer than I can capture in the field of view of my telescope!
Even with a tracking mount and dark sky, processing a comet moving relative to the stars is still really challenging, and I really benefited from following the “Standard Comet” example in Adam Block’s Comet Academy.
Earlier this month, we were very lucky and happened to be at my favorite dark sky site – Dell City, Texas – when I got an alert on my phone that we might have a Kp8 geomagnetic storm coming the next day, with a chance to see the Northern Lights much lower than usual.
I have the app on my phone because we’ve traveled to places where seeing the Northern Lights was possible. We even saw them on the horizon from Inverness, Scotland. We’ve also been on two trips where Northern Lights tours were on the agenda – but both tours were cancelled due to weather. Earlier this year, when there was another big geomagnetic storm, we went north to Conroe, Texas where people reported seeing the lights. I found a great foreground – but alas, no lights.
So imagine my delight when I was setting up my telescope in Dell City, Texas, where the skies are very familiar to me, and I looked up and saw moving red lights to the north. Red lights to the north are not normal. The Northern Lights were visible from Texas! I literally sprinted into our Air B&B to get my husband and my camera.
I took glamour shots of my telescope with the aurora.
I took glamour shots of our Air B&B with the aurora.
I made some time lapse movies.
Camera geek info:
Canon EOS 60D in manual mode, 5 – 10 second exposures, ISO 1600
Rokinon 14 mm f2.8 lens, manual focus
Intervalometer
Tripod
And I’m left with the question: when can we see this again? It was amazing.
I was looking through my comet posts after my post yesterday, and I discovered I hadn’t posted this image of Comet PANSTARRS C/2021 S3 with two globular clusters that I made last spring. Enjoy!
I hadn’t planned on imaging comets when we were in Dell City last spring, but when I saw this combination of two globular clusters and comet PANSTARRS C/2021 S3, I knew I had to try it.
Globular cluster M9, the brighter one to the left, is 25,800 light years away from us. It’s 90 light years across, giving it an apparent size of 12 arcminutes. Globular cluster NGC6356, the smaller one to the right, is 49,200 light years away from us. Its apparent diameter is 8 arcminutes, giving it a diameter of 115 light years across. Globular clusters are mind-bogglingly old parts of our galaxy and can be used to infer the age of the universe. There are some interesting open questions about them, including their exact ages and whether they formed as part of our galaxy or were accreted later (probably a mix of both). In the paper I found giving the ages for these two globular clusters, it shows that M9 is 14.60 ± 0.22 billion years old with one model, 14.12 ± 0.26 billion years old with a second model, and 12 billion years old in the literature. It shows that NGC6356 is 11.35 ± 0.41 billion years old with one model, 13.14 ± 0.64 billion years old with a second model, and 10 billion years old in the literature. No matter which age ends up being correct, ~10 billion years old is amazingly OLD!
Comet PANSTARRS C/2021 S3 was discovered by the Panoramic Survey Telescope and Rapid Response System located at Haleakala Observatory, Hawaii on images taken on September 24, 2021. It reached perihelion (its closest point to the sun) on February 14, 2024 (the day after this image was taken) at 1.32 AU distance. Its orbital eccentricity is higher than 1, meaning it’s on a parabolic trajectory and isn’t coming back.
I feel very fortunate that my trip out to the dark skies was timed so I could image this comet with two ancient globular clusters. I also feel fortunate that I imaged it in a time when so many processing tools are being developed to make processing the image so much easier! The tools I have this year are so much more powerful than the ones I had last year.
Camera geek info:
Williams Optics Zenith Star 73 III APO telescope
Williams Optics Flat 73A
ZWO 2” Electronic Filter Wheel
Antila LRGB filters
ZWO ASI183MM-Pro-Mono camera
ZWO ASiair Plus
iOptron CEM40
Dell City, Texas Bortle 2-3 dark skies
Frames:
February 13, 2024
Interleaved LRGB lights
5 60 second Gain 150 L lights (only used for the comet)
On Sunday morning, we got up at 4:00 AM to drive to a spot with a long view to the East to go comet hunting. I successfully got the telescope set up prior to the time when Comet Tsuchinshan-ATLAS C/2023 A3 was supposed to rise. However, when the comet did rise, the ASIAIR could find stars, but couldn’t plate solve to figure out if it was pointing exactly right. So I ended up starting imaging without having successfully scanned to the predicted comet location. Since I could see a tiny comet in the first shot, I let the system take an automated sequence of shots. 60 second shots were too bright, so I started with 10 second shots, and when they became too bright, I switched to 1 second shots.
I also tried taking pictures with an 85 mm lens on my Canon EOS 60D, but that didn’t pick up the comet at all. What it did pick up was the reason I didn’t get very many good comet images … clouds! Of course, clouds are terrible for astrophotography, but they do lead to nice sunrise pictures.
We stayed for the sunrise, went out to breakfast, and then headed home.
Astrophotography is really two hobbies: capturing the images and processing them.
When we got home, I worked on processing the images I’d gotten. I could see the comet in the 10 second images and in the 1 second images, but the 1 second image ones were generally partially through the clouds. So I ended up using only the 10 second images. Because there weren’t any stars captured in these short images, I only needed to process for the comet and use Comet Alignment to align the frames.
I’m hoping that I’ll get some better images later this fall. Are you making plans to try to see this one?
M27, also called the Dumbbell Nebula or Apple Core Nebula, is a planetary nebula – the gases expelled from a red giant star before it becomes a white dwarf, lit up by that star. It’s located in the Milky Way, approximately 1250 light years away, and it has an apparent size of 8 arcmintues, making it 2.9 light years across. It’s estimated to be 12,700 years old.
Planetary nebulae do not last long on an astronomy time scale because the expelled gases grow dimmer as they expand away from the central star. I am glad I live in a time when we can observe them and they can be observed!
Planetary nebulae were originally called that because they looked like a round (like a planet) ball of fuzz by visual observers. However, now we know they have nothing to do with planets and are actually shell(s) of gas expelled from a red giant star. With astrophotography, we can pick up so much more detail than a fuzzball, and so we end up with interesting names. For this nebula, some thought the inner core of this nebula looked like a dumbbell; others thought it looked like an apple core. With the outer fringe, what do you think it looks like?
I used data from my driveway in Friendswood, Texas with suburban Bortle 7 – 8 brightness skies (lots of light pollution) to make this image. In order to capture the outer fringe I needed a lot of data: 12.2 hours of Ha data and 10.65 hours of Oiii data, taken over nine nights.
This is a narrowband image, mapping Oiii to blue and Ha to red. My goal was to capture both the details in the core and the outer fringe. It took three processing tries, but I think I was ultimately successful.
NGC6357, the Lobster Nebula, is an emission nebula. It is a large star-forming region containing three star clusters, many young stars, and some massive stars. One cluster is Pismis 24, located just above the bright blue core in this picture. The stars in this cluster are about 1 million years old and four are massive – 40 – 120x the mass of our sun, among the most massive stars in our galaxy. The Lobster Nebula is located in the Milky Way, approximately 5550 light years away, and it has an apparent size of 60 x 45 arc min, so it is approximately 97 x 73 light years across.
From my driveway, the Lobster Nebula is low to the South and is only visible for a short time from when it rises above my house to when it goes behind the pine tree. So it took many nights of data collection to get enough data to make this image – 12.2 hours of data collected over 13 nights. And it would still benefit from more! I may collect more data the next time we visit the dark skies of Dell City, Texas, where I have an unimpeded view to the South. But, until then, I have declared the end of Lobster season!
Although NGC6357 is traditionally named the Lobster Nebula, I think it looks like a bug-eyed monster. And a bug-eyed monster should be green with a red core and have red eyes. So in addition to the traditional Hubble SHO (Sii mapped to red, Ha to green, and Oiii to blue), I also made a version using a OHS (Oiii mapped to red, Ha to green, and Sii to blue) palette. I thought this version produced a nice contrast in the pillar in the core near the Pismis 24 cluster.
I call this image The Blue Swan with the Golden Egg. Can you see the blue swan sitting on a purple nest with a golden egg?
M17 is an emission nebula with many names, including the Swan Nebula. When I saw the Oiii narrowband images, I finally understood why it is called the Swan Nebula, and I’ve oriented this image so that the swan is “floating” with its head up. If you see the two dark spots near the center of the frame and the brightest part of the nebula, the lower one is the swan’s neck. The largest portion of the bright part of the nebula is the swan’s body, the neck comes up past the dark spot, and then the head is above it. I’ve included a single frame, below, where it the swan is more obvious because the rest of the nebulosity is hidden, and I’ve sketched in the swan on top of it. Howard Banich has some lovely hand-drawn sketches of this nebula in a Sky & Telescope article.
M17 is a large star-forming region. It’s been the home for three star-forming events, but the stars created are mostly hidden behind the molecular cloud. The massive stars it made emit UV radiation that excites the hydrogen gas to form the emission nebula. It’s located in the Milky Way, approximately 5500 light years away, and the brightest portion has an apparent size of 10 arc min, so it is approximately 15 light years across. The region of gas around it is larger, with an apparent size of about 30 arc min, so it is approximately 48 light years across.
I have learned a lot about narrowband processing while working on this image, and I’ve gotten a lot of useful pointers from the folks at the astrobin forums.
I initially made four different color maps using NBColourMapper, with the following color assignments and results:
Palette Name
Natural
Hubble (SHO)
Canada France Hawaii Telescope (HOS)
Extra
H-alpha color mapping
Red (0)
Green (120)
Red (0)
Red (0)
Oiii color mapping
Turquoise (180)
Blue (240)
Green (120)
Blue (240)
Sii color mapping
Orange (20)
Red (0)
Blue (240)
Green (120)
Result
Mostly red, not much color contrast
Blue Swan with Green/Yellow nebula, more color contrast
Yellow Swan with Pink/Purple Nebula, more color contrast
Pink/Purple Swan with Yellow/Purple nebula, more color contrast
My Hubble SHO pallet was extremely green and looked nothing like the classic Hubble images which tend to be very blue and yellow/red. Apparently mostly green images are not considered attractive (it’s not easy being green) and don’t have the desired contrast. After getting feedback on the astrobin forum and watching a lot of videos, I learned that the general technique for narrowband color mapping is to first normalize the images using LinearFit so the different bands are all equally bright. This loses the relative signal strengths of the different bands, but means that the dimmer bands aren’t overwhelmed by the stronger ones.
After color mapping the three linear fit data sets and running NBColourMapper, I used Dynamic Background Extraction to remove the background color bias. I liked what it did with the background more than Background Neutralization, which I also tried.
For color calibration, I tried using SPCC in narrowband mode. This seemed to want to push the nebula back to the original colors – very green for SHO and red and gold for HOS (which I actually liked). This makes sense, but I didn’t end up using the resulting images. I tried using ColorCalibration. This brought out the reds and golds in the SHO image, but it ended up with extreme colors in the nebula.
I got more astrobin advice and watched some Adam Block videos. Not only does Adam provide excellent explanations of the effects of various tool settings (the “why” as well as the “what”), but he also talks about his image processing philosophy, which in this case was eye-opening for me. He shared his philosophy of thinking about how he wanted the image to look when it was done before he started processing it which I found extremely useful. He gave me a different and better way to think about narrowband astrophotography image processing. I looked at my original narrowband data and decided what I’d like to try to do is bring out the details that are in the Sii data. Following a similar philosophy to what he did in his example, I used PixelMath to map the narrowband data to RGB, emphasizing the red and the blue and dialing back the blue and the green when there was red to emphasize the red Sii details with the following settings:
R = 2*S
G = 0.4*H+0.6*H*(1-S)
B = O+2*(1-S)*O
I finally achieved the blue I’d been looking for!
After narrowband mapping, I stretched the nebula using ScreenTransferFunction and the HistogramTransformation, then used a new to me tool, High Dynamic Range Multiscale Transform (HDRMT), which “flattened” the image so that I could see details in both the nebula core and in the surrounding faint nebula. I finished by using Curves, working on the c curve to emphasize the reds a little more (after the PixelMath mapping, I didn’t need to do much in Curves).
With this color mapping, the stars turn out over-blue. I processed them separately and converted them to be only white, then added them back in.
This has taken me a couple of weeks of learning and experimenting, and I think it was worth it. I ended up with an image that makes me think “isn’t the universe beautiful?”
T Coronae Borealis (T CrB) (left of center in the image) is nicknamed “the Blaze Star” because it is a recurrent nova. It consists of two stars: a white dwarf and a red giant. Most of the time, the visible star is the red giant. However, over time, matter from the red giant is transferred to the atmosphere of the white dwarf, and, periodically, the white dwarf heats the matter hot enough to cause runaway fusion, rapidly making the white dwarf brighten, causing a nova event.
The last two times this star went nova were May 12, 1866 and February 9, 1946. It is expected to go nova again soon, possibly this summer.
T CrB is located in the Milky Way, approximately 2,630 light years away, so many cycles of novas may have occurred that we have not seen yet because the light hasn’t reached us! But it’s on the way!
My husband suggested that I should capture a “before” picture to compare with a picture during the nova.
I used PixInsight to annotate the image with the star magnitudes, so you can see that the magnitude for T CrB is consistent with its non-nova state (magnitude 10.25 vs its expected nova magnitude of 2 – 4).
When I annotated the image, I noticed that there was a bright visible line that was not marked. I suspected, given it was a line, indicating something moving slowly across the frame, that it was an asteroid, so I added annotation for asteroids to discover that it is the asteroid 2 Pallas. The “2” in its name means it was the second asteroid to be discovered. 2 Pallas is a main belt asteroid, orbiting between Mars and Jupiter, in an unusually highly inclined (angle of orbital plane relative to the invariable plane) (Pallas’s inclination is 34.43 degrees; Vesta’s is 5.58 degrees; Earth’s is 1.58 degrees) and highly eccentric (more elliptical) orbit (Pallas’ eccentricity is 0.28; Vesta’s is 0.089; Earth’s is 0.017; 0 eccentricity is a circular orbit).
Because I am now using a monochrome camera, I have to cycle between filters to get color. I was cycling in 20 minute intervals, so the color of 2 Pallas looks like a rainbow, shifting between colors. This is not a feature of the asteroid but rather a feature of my processing, but I think it is rather fetching.
This is the first time I’ve captured an asteroid! How cool is that?
Are you looking forward to spotting the nova when it comes?
Starlink is SpaceX’s megaconstellation of satellites, which provides global mobile broadband communication. It currently consists of over 6000 satellites. The satellites have recently been launched in sets of 20 – 23 satellites on a single Falcon 9 rocket that are initially released one after another into the same orbit, so they appear to follow one another across the sky in a “train”.
Starlink satellites are visible when the sky is dark but they are still sunlit, so just after sunset/before sunrise. They are easiest to see within a couple of days of launch, when they are in the orbit raising phase and are closer together and lower. Once they reach their final orbit, they are harder to see. Because of concerns raised by astronomers over the effect of such a large number of satellites on astronomical observations (satellites create streaks of photobombing light on astrophotos), SpaceX has implemented two things to reduce their brightness: 1) made the satellites invisible to the naked eye within a week of launch by changing their attitude during orbit raising so the solar arrays won’t reflect sunlight down to the Earth and 2) made them less bright on orbit by deploying sun visors on the satellites so the chassis won’t reflect sunlight down to the Earth.
On Monday, June 24, the FindStarlink app/website predicted we’d have good visibility for a Starlink train, so we went outside to check it out. The “train” of satellites was really striking as it rose at the end of our street and traveled in a line across the sky, then went into the Earth’s shadow and disappeared just as the satellites “reached” a bright star (it could have been Pacmac gobbling up dots). Given the date and that 22 satellites were visible in the train, I think this was Starlink Group 10-2 (the FindStarlink site says what train is visible, but I forgot to record that on Monday).
I thought they were a really cool thing to see, but I am also glad that SpaceX is working on making them less of a nuisance to astronomers.
Camera geek info:
Panasonic DC-GX9 set at f/2.5, 15 second exposure, ISO 3200
Space&Aliens 