The Pleiades (M45) & an Unexpected Visitor

This week, I aimed my telescope at the Pleiades (M45) and captured a stunning image. However, the real story unfolded an hour into the shoot when I encountered an unexpected visitor. I decided to bring out my larger telescope and set up my Apertura 60mm Refractor connected to an ZWO ASI533MC camera. I focused the scope, polar aligned the mount, and pointed the telescope towards M45 to commence a 5-hour imaging session. Everything seemed to be running smoothly, so I went inside to warm up.

After an hour of shooting, I logged in to the control computer to ensure everything was still functioning optimally. I reviewed the 60-second exposures until I noticed something peculiar on image 61. There was a pulsating streak of light running halfway through the frame, and this light persisted on image 62.

Typically, a pulsating streak of light across an astro image is caused by an airplane crossing the frame. However, airplanes usually have three streaks of light—two for their navigation lights and one for their tail light. Additionally, airplanes move swiftly across the night sky. Since I was shooting 60-second exposures, this object took approximately two minutes to traverse a relatively small field of view.

Seeking assistance in Natzronomy’s Discord server, a user directed me to Stellarium and explained how to increase the object labels for satellites. By setting the app to the exact time the images were taken, we were able to identify the object as a discarded Chinese rocket body launched in 2023 under the designation CZ-3B. We could then search for information about the rocket and found a video and photos of its launch.

I was astounded to witness the launch of an object that I had just photographed orbiting in space, 12,500 kilometers away. Furthermore, analyzing the pulsations of light in the image revealed that the rocket body was tumbling at approximately 3.5 rotations per minute. What a happy little accident.

Once I brought everything inside, I downloaded the calibration and light frames from the control computer. However, I noticed that I had quite a bit of movement in my mount or some rogue clouds, as I lost almost exactly an hour’s worth of frames due to oblong stars or generally fuzziness.

I stacked the remaining frames in PixInsight using the weight batch pre-processing script. I then trimmed the edges with a dynamic crop and applied GraXpert to remove the background gradient. After restoring astrometric data, I used Seti Astro’s background picker and applied Spectrophotometric Color Calibration with the selected background as the region of interest.

I applied BlurXTerminator and NoiseXTerminator with their default settings, then stretched the image with a standard histogram transformation stretch. Finally, I removed the stars with StarXTerminator and set the star image aside for a moment.

I was quite pleased with the color and saturation from the initial stretch, so I made some minor adjustments to the luminance channel using the curves adjustment tool to enhance the contrast. I then combined the star and starless images in Pixel Math using the formula ~(~Starless*~Stars) and exported the final image.