2022: Missouri – Diamonds on a Black Velvet Sky – Imaging of M45 “Pleiades.”

Another Astrophotographer adventure is here – it’s the 19th of November, 2022 in the Midwest, I arrived at the Bortle Class 4 location at 4:00 pm, and sunset was at 4:46 pm, this gave me enough time to set the tripod, and mount the telescope prior to sunset. Accompanying me on this trip was my friend Bill, he was already in situ when I arrived and was already setting up his gear. It was going to be a cold night, with possible plunging lows between 19°-15° Fahrenheit. 

 

 

About the Target

 

Messier 45 – Open Cluster M45, type ‘b’ in Taurus – Coordinates: RA 3h 47m 24s | Dec +24° 7′ 0″, Distance to earth: 444.2 light years, Radius: 17.5 light years, Magnitude 1.6, Constellation of Taurus, Color: hot blue. There are references to the Pleiades in the Odyssey, the Bible, and the Quran, and it is also revered in Hindu mythology. Mentioned by Homer about 750 B.C., by biblical Amos about 750 B.C., and by Hesiod about 700 B.C. The Pleiades, also known as Messier 45 (M45), are among those objects which are known since the earliest times. At least 6 member stars are visible to the naked eye. At the same time, under moderate conditions, this number increases to 9, and under clear dark skies jumps up to more than a dozen (Vehrenberg, in his Atlas of Deep Sky Splendors, mentions that in 1579, well before the invention of the telescope, astronomer Moestlin has correctly drawn 11 Pleiades stars, while Kepler quotes observations of up to 14).

The Pleiades also carry the name “Seven Sisters”; according to Greek mythology, the Pleiades are the seven daughters of the “father” Titan Atlas “mother” Oceanid Pleione: Alcyone, Asterope (a double star, also sometimes called Sterope), Electra, Maia, Merope, Taygeta and Celaeno. It was said that after Atlas was tasked to carry the heavens on his shoulders, the hunter Orion began to pursue the Pleiades. To protect them Zeus transformed them into doves, and then into constellations, to comfort their father. The constellation of Orion still pursues the Pleiades across the night sky. This pursuit is apparent in a timelapse video of these two objects. 

In Japan, the Pleiades are called “Subaru”, and the car company of the same name uses the Pleiades as their company logo.

The Persian name is “Soraya”, after which the former Iranian empress was named. Old European (e.g., English and German) names indicate they were once compared to a “Hen with Chicks”. Other cultures tell more and other lore of this naked-eye star cluster. Ancient Greek astronomers Eudoxus of Knidos (c. 403-350 BC) and Aratos of Soloi (c. 310-245 BC), in his Phainomaina (c. 270 BC), listed them as their own constellation: The Clusterers. Admiral Smyth also refers to this in his Bedford Catalog. 

The Pleiades is one of the best-known star clusters in the entire sky. It is easily visible to the naked eye on Winter evenings from the Northern Hemisphere. Located in the constellation of Taurus, the Pleiades forms a tiny dipper-shaped asterism in the shoulder of the Bull.

The Pleiades nebulae are blue-colored, which indicates that they are reflection nebulae, reflecting the light of the bright stars situated near (or within) them. The brightest of these nebulae, that around Merope, was discovered on October 19, 1859, by Ernst Wilhelm Leberecht (Wilhelm) Tempel at Venice (Italy) with a 4-inch refractor; it is included in the NGC as NGC 1435. The nebulae around Alcyone, Electra, Celaeno and Taygeta were found in photographs in the later 1880s. The first Astro cameras revealed the full complexity of the Pleiades nebulae, e.g. by that of the brother’s Henry in Paris and Isaac Roberts in England, between 1885 and 1888. In 1890, E.E. Barnard discovered a starlike concentration of nebulous matter very close to Merope, which found its way into the IC as IC 349. The analysis of the spectra of the Pleiades nebulae by Vesto M. Slipher in 1912 revealed their nature as reflection nebulae, as their spectra are exact copies of the spectra of the stars illuminating them.

Physically, the reflection nebula is probably part of the dust in a molecular cloud, unrelated to the Pleiades cluster, which happens to cross the cluster’s way. It is not a remainder of the nebula from which the cluster once formed, as can be seen from the fact that the nebula and cluster have different radial velocities, crossing each other with a relative velocity of 6.8 mps, or 11 km/sec. Even with the naked eye and under modest conditions, the Pleiades are rather easily found, roughly 10 degrees north-west of the bright red-giant star Aldebaran (87 Alpha Tauri, mag 0.9, spectral type K5 III). This is a very appealing spectacle, especially for amateurs with less expensive equipment (actually, you can observe it with the naked eye, but even the smallest binoculars or telescopes will increase observing pleasure.

 

Polar alignment Process

Sunset occurred at 4:45 pm and by that time I had my imaging rig mounted – I would like to think that I have refined my workflow setup, which now takes less than 10 minutes – which includes setting the tripod to face NCP, and then mounting the imaging rig (with all components) to the tripod. With everything in its place, I glanced up in the sky and was able to see the faint gleam of Polaris, my imaging rig was pointed in the general area in the night sky. I was able to achieve polar alignment in less than 1 minute. Next, I balanced the imaging rig for both the RA and Declination and it was spot on. Now I wait for astronomical twilight to end, which was 645pm. 

 

Imaging Capture Workflow

I also set the mount to perform auto meridian flip – An Automatic Meridian Flip operation swaps the telescope to the west side of the mount. Meridian flips prevent your telescope and camera bump into the mount and doing major damage to your equipment.

I also did my initial guiding, polar alignment, plate solving and electronic auto-focus before beginning my night’s imaging session. 

 

Imaging gear list

Mount: SWSA, Control: ZWO ASIAIR, Guide Camera: ZWO ASI 120MM, Guide: William Optics UniGuide 32mm, Scope: William Optics RedCat 51, Camera: ZWO ASI533MC, Focuser: ZWO ASI EAF, Filter drawer: Starizona M42 Modular, Filter Used: Optolong L-Pro, Central Power Pegasus Astro Powerbox Advance and Dew Heathers: Agena Astro dew heater.

 

The Imaging Session

I started imaging at 7:01 pm. As mentioned above, the target is M45 “Pleiades”, by entering the object number,  “Select and GoTo Target”, this will slew the mount to the target position in the sky, and then validate if the target is in the center or not. Once centered, I set up multi-star guiding and one final autofocus, prior to starting the imaging session.

I automated my entire night’s workflow, using the “autorun” tool. I created flats frames, light frames, dark frames and bias frames.

Flat Frames: 40 x 3-sec exp, using a led light panel.

Light Frames: 60 x 120-sec exp, 60 x 30-sec exposure and 60 x 180-sec exp.

Dark Frames: 60 x 120-sec exp, 60 x 30-sec exp and 60 x 180-sec exp, lens cap on the scope.

Bias Frames: 60 x 0.01 sec-exposure.

I did forget to do one step, while it’s not critical to imaging in this session, it is still helpful. So what did I forget; I forgot to use the DSO Stacking feature in the AA, I could have stacked 10-20 lights (no calibration frames) which would give a preview, and I could have edited the histogram, a crop and rotated if warranted.

With everything set, I can head back to the car to warm up, I have 4 hours and 59 minutes until the meridian flip. I also checked the weather forecast – The initial forecast called for a chance of cloud cover, possible humidity and wind gusts. But this night was perfect; no clouds and excellent seeing. 

Things went very smoothly, and when it was time for the meridian flip, I stood by and watched as the computer, instructed the mount to perform the flip. It was a relief to see that all go as planned.  Bill and I would check our imaging rig and imaging session, every hour or so; repeating this process until the night’s session ended at 430pm.

 

Now onto the fun – Image Processing with Pixinsight

This will be my second attempt at image processing using Pixinsight software, I must admit the initial learning curve took me almost two weeks to grasp, and there is still much more to learn, but I have a decent level of understanding, enough to move onto the paid version after the trial ends.

My workflow consists of, 264 Light images with 264 Dark, 40 Flat and 30 Bias images, which are processed and registered in Pixinsight software and, then stacked in order to get a single image you can process. This automated workflow process is referred to as Weighted batch Pre Processing, the total runtime of the process is 1 hour and 49 minutes.

Since I shot the image using three different exposures, I readied the image import to Pixinsight as a process and used the HDRComposition as the first pass. Next, I did a Screen Transfer – which is a stretch of the image; taking it from a black point, and then revealing RGB color. Once I was happy with the RGB color, up next was the Automatic Background Extractor and EzDenoise. Now onto the color calibration section. Getting a matched color of M45 is challenging, imaging at multiple exposures will get you close to an accurate dynamic range, so all I had to do in the Histogram transformation was bump the RBG and Saturation Channels – this really helped in separating the stars from the nebulosity. Next, I did a mild Star reduction using StarNet2. After this, I felt that this was enough post-processing.  I am still new to Pixinsight, and there is much more to discover.

Until the next adventure.

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