astro

This was my first time using a star tracker. This allowed me to capture the Milky Way in much more detail and with less noise than in any of my previous shots.

I mounted my camera on a star tracker (motorised equatorial mount; Sky Watcher – Star Adventurer 2i) to follow the position of the stars throughout a series of long exposures. I took 13 light frames of the Milky Way center, each at a 4-min exposure time. I also took a single frame of the foreground at a 12-min exposure. Finally, I took 10 dark frames to allow for noise reduction during image processing.

IMAGE PROCESSING

I did the initial image processing in StarStaX (v. 0.9): using the dark frames to subtract noise from light frames and subsequently, stacking (averaging) all light frames to generate a single image of the Milky Way. I then did my further processing in Adobe Photoshop, adjusting light curves, colours and details, and finally, blending the images of the Milky Way and the foreground.

TECHNICAL DETAILS

Location: Boca Tauce – Ethnographic Museum, Teide National Park, Tenerife (φ 28°12'46.3"N, λ 16°40'52.1"W)
Date and time: April 28 2022, 5:13 local time
Sky frames: 13 frames | 4 min exposure time each | f/4 | ISO 800 | 24 mm
Foreground frames: A single frame | 12 min exposure time | f/4 | ISO 800 | 24 mm
Dark frames: 10 frames | settings same as for sky frames
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 24–70 mm f/4 S

This image is the product of a cold and sleepless—and wonderful—night in the dark. In the Cañadas caldera, at an elevation of about 2,000 meters, I chose a spot that would give me this particular composition: a frame centered on Polaris in the sky, and below, the Teide volcano and the dramatic rock formations of Roques de García. In this particular night, as I had carefully planned it, the International Space Station (ISS) also passed through the chosen field of view (second image contains only the 9 frames of the ISS transit).

Between 2:01 and 5:48 AM (3 h 46 min), I took a total of 663 consecutive 20-second exposures, which I later stacked using software. Just before twilight, I also took a 7-minute exposure of the foreground to capture all its details with minimal noise. The moon was almost full, shining bright, creating the contrast and dramatic shadows in the landscape. 

Star trails show the apparent motion of the stars across the night sky as Earth rotates about its axis. This causes stars to rise in the east and set in the west, just like the Sun and the Moon. Polaris, also known as the North Star, is a relatively bright star, near the North Celestial Pole (0.7 degrees separation). The North Celestial Pole—and Polaris by approximation—is the pivot point directly north of Earth around which the stars circle daily. It takes 23 h 56 min and 4 sec to complete a circle, which is about 4 minutes less than the solar day, and equals the time it takes Earth for a complete rotation (Earth's rotational period = star/sidereal day on Earth). The solar day is slightly offset due to Earth's orbit around the sun (3.9 min * 365 days ≈ 24 h). Since we know Earth's rotational period, we can calculate the angle of the arc, that the stars have completed during the 3 h and 46 min of imaging: The sky shifted by about 56.4° (360° / 23.93 h * 3.75 h).

The ISS traversed the field of view at around 5:35 AM and created the bright straight trail going across the image. The ISS was by far the brightest object in the frame—it can reach levels of brightness in the night sky that are only surpassed by the Sun and the Moon. You can find out when the ISS passes over you at https://heavens-above.com/PassSummary.aspx?satid=25544 and on various apps.

IMAGE PROCESSING

After some initial adjustments in Adobe Lightroom (white balance, saturation, tone curve), I exported the image raw files as JPEGs for stacking. I used StarStaX (v. 0.9) for stacking all 663 frames of the sky, saving all intermediates in addition to the final stacked image. From the intermediates (JPEGs), I later created a time-lapse movie in Photoshop (see next section). I saved the final image as TIFF and edited it in Adobe Photoshop, first using the healing tool to remove hot pixels as well as trails from meteors, satellites and airplanes. I then manually corrected for vignetting, adjusted the tone curve and saturation, and applied Gaussian blur and some noise reduction to smoothen the trails. Finally, I opened the image of the foreground as a layer in Photoshop, edited it (white balance, tone curve, gradients, hot pixel removal, etc.) and selected the sky for transparency, blending the two images to create the final picture.

TIME LAPSE

I imported all the intermediate frames of the cumulative stacking process in sequential order into Adobe Photoshop to generate a video at 24 frames per second. I copied and applied some of the same filters I used for editing the final star trail image. I blended each frame with the same image of the foreground, which therefore remains static.

TECHNICAL DETAILS

Location: Llano de Ucanca, Las Cañadas del Teide, Tenerife (φ 28°12'40.6"N, λ 16°38'06.4"W)
Date and time: May 15, 2022 | 2:01 – 5:48 local time
Sky frames: 663 frames collected over 3 h 46 min | 20 sec exposure time each | f/4 | ISO 800 | 24 mm
Foreground frames: A single frame | 7 min exposure time | f/8 | ISO 800 | 24 mm
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 24–70 mm f/4 S

IMPROVEMENTS FOR NEXT TIME

• use a lower ISO for the foreground to reduce noise

• take dark frames for noise reduction

• take flat frames for vignette control

• turn off the in-camera vignette correction to avoid distortion patterns during stacking

• also catch the sunset or sunrise for the time lapse

• turn off exposure delay mode for smoother star trails

Just as I was setting off for a sunrise hike, I came across this chapel, which provided a great scale and foreground for a composition with the mountains and the Milky Way. Unfortunately, I was in a bit of a hurry, but I am glad I stopped to take a shot. During this moonless night, the Milky Way's galactic center was shining bright above the Ermita de Nuestra Señora de las Nieves chapel in the Cañadas caldera. The long exposure revealed some high (cirrus) clouds, faintly illuminated by the distant city lights.

This is a composite of two separate exposures, a 20-second exposure for the sky and a 5-minute exposure for the foreground. The sky portion lacks detail and is quite noisy, given the single (untracked) exposure and the high ISO.

IMAGE PROCESSING

I edited frames of both the foreground and the sky in Adobe Photoshop, adjusting light curves, colours and details, and finally, blending both images.

TECHNICAL DETAILS

Location: Ermita de Nuestra Señora de las Nieves chapel, Las Cañadas del Teide, Tenerife (φ 28°13'26.9"N, λ 16°37'40.5"W)
Date and time: May 2, 2022, 5:10 local time
Sky frames: A single frame | 20 sec exposure time each | f/4 | ISO 3200 | 24 mm
Foreground frames: A single frame | 5 min exposure time | f/4 | ISO 3200 | 24 mm
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 24–70 mm f/4 S

In my first attempt using a more sophisticated telescope setup for deep-sky imaging, I captured the magnificent Pinwheel Galaxy (Messier 101). Situated some 21 million light-years away from Earth in the Ursa Major constellation, this spiral galaxy presents a stunning face-on view. Its asymmetry results from interactions with its smaller companion galaxies. Atmospheric conditions were less than ideal due to the jet stream over the Canary Islands, impacting sharpness in the final result. I gathered 21 frames over 7 hours, each with a 21-minute exposure (one frame was later discarded), revealing the distant beauty of the Pinwheel Galaxy.

IMAGE PROCESSING

I processed the raw images in PixInsight software and did some final and quick editing in Adobe Lightroom. Already starting with prepared "master" flat and dark frames, I used these for calibrationg all light frames, followed by debayering and image alignment. I then integrated the preprocessed light frames, applied color calibration and histogram stretching. I then used the "photometric color calibration" tool, followed by another round of histogram transformation. Lastly, I did some final and quick touchups in Adobe Lightroom. 

TECHNICAL DETAILS

Location: Boca Tauce – Ethnographic Museum, Teide National Park, Tenerife (φ 28°12'46.3"N, λ 16°40'52.1"W)
Date and time: May 9–10 2021, 22:36–5:58 local time
Light frames: 20 frames | 21 min exposure time each
Dark frames: Number and settings unknown
Flat frames: Number and settings unknown
Telescope and setup: Ritchey–Chrétien telescope (12-inch diameter primary mirror); focal length reducer; off-axis guider; active dithering
Camera/sensor: Actively cooled ZWO camera with an APSC sensor (20 MP, colour)

This was one of my first attempts at imaging the Milky Way with my new full-frame camera setup. For this image, I used an ultra-wide-angle lens, which I had rented specifically for this purpose. This allowed me to capture a large portion of the Milky Way, using a fairly long exposure.

Bryce Canyon National Park in Utah provided a perfectly dark night sky. This image is a single 30-sec exposure, looking towards the Milky Way core. Jupiter is the brightest object in the frame, just besides the trees in the front. I briefly illuminated the trees in the foreground using my flashlight.

TECHNICAL DETAILS

Location: Bryce Canyon National Park, Utah (φ 37°30'60.0"N, λ 112°15'52.7"W)
Date and time: July 6, 2019, 2:34 (MDT)
Sky and foreground frames: A single frame | 14 mm | f/4 | ISO 3200
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 14-30mm f/4 S

I took this image series just after twilight at a beautiful viewpoint on Tenerife (Mirador de Chipeque). The Teide volcano is visible on the left and the neighboring island of La Palma is to the right. Below are the city lights of several municipalities including Puerto de la Cruz and La Orotava. In this composition, I was able to direct the field of view west, approximately centering onto the celestial equator. Thereby, I captured straight star trails in the center of the image, with trails arching left or right the further they are from the center of the image (and the celestial equator). The North Celestial Pole is not visible but would be to the right of this field of view.

Between 22:19 and 2:41 AM (4 h 22 min), I took a total of 764 consecutive 20-second exposures, which I later stacked using software. The near full moon rose just after I started imaging, illuminating the landscape and dynamically creating shadows in the foreground, as you can see in the time lapse. You can also see several ships moving across the ocean, cars driving up the mountain, clouds moving in and some low clouds forming above the cityscape.

Star trails show the apparent motion of the stars across the night sky as Earth rotates about its axis. This causes stars to rise in the east and set in the west, just like the Sun and the Moon.

IMAGE PROCESSING

After some initial adjustments of both light and dark frames in Adobe Lightroom (white balance, saturation, tone curve), I exported the image raw files as JPEGs for stacking. I used StarStaX (v. 0.9) for stacking all 764 frames, using the 86 dark frames for noise reduction. In addition to the final stacked image, I also saved all intermediates of the stacking process (JPEGs), from which I later created a time-lapse movie in Photoshop (see next section). I saved the final image as TIFF and edited it in Adobe Photoshop, duplicated the image as layers to edit the sky and the foreground separately. I used the healing tool to remove hot pixels as well as trails from meteors, satellites and airplanes. I then manually corrected for vignetting, adjusted the tone curve and saturation, and applied Gaussian blur and some noise reduction to smoothen the trails. Finally, I selected the sky for transparency, blending the two layers to create the final image.

TIME LAPSE

I imported all the intermediate frames of the cumulative stacking process in sequential order into Adobe Photoshop to generate a video at 24 frames per second. I copied and applied some of the same filters I used for editing the final star trail image.

TECHNICAL DETAILS

Location: Mirador de Chipeque, Tenerife (φ 28°22'26.9"N, λ 16°27'49.9"W)
Date and time: May 16, 2022 | 22:19 – 2:41 local time
Sky and foreground frames: 764 frames collected over 4 h 22 min | 20 sec exposure time each | f/4 | ISO 640 | 24 mm
Foreground frames: No separate frame; used stacked foreground
Dark frames: 86 frames | settings same as for light frames
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 24–70 mm f/4 S

These are the first two star trail images I ever took. The ultra-wide-angle lens allowed me to capture both the North Celestial Pole and the celestial equator in the same field of view (first image), which illustrates the star trails arching and their apparent speed of motion across the sky, both depending on the star's position relative to Earth's rotational axis.

Star trails show the apparent motion of the stars across the night sky as Earth rotates about its axis. This causes stars to rise in the east and set in the west, just like the Sun and the Moon. Polaris, also known as the North Star, is visible in both images. It is a relatively bright star, near the North Celestial Pole (0.7 degrees separation). The North Celestial Pole—and Polaris by approximation—is the pivot point directly north of Earth around which the stars circle daily. 

Straight trails originate from airplanes, satellites or meteors. 

IMAGE PROCESSING

After some initial adjustments of both light and dark frames in Adobe Lightroom (white balance, saturation, tone curve), I exported the image raw files as JPEGs for stacking. I used StarStaX (v. 0.9) for stacking all light frames, using the dark frames for noise reduction. I saved the final image as JPEG and did some light editing in Adobe Lightroom.

TECHNICAL DETAILS

Location: Bryce Canyon National Park, Utah (φ 37°30'60.0"N, λ 112°15'52.7"W)
Dark frames: 3 frames | settings same as for light frames
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 14-30mm f/4 S
Foreground frames: No separate frame; used stacked foreground

First image

Date and time: July 6, 2019 | 4:44 – 5:38 local time

Sky and foreground frames: 103 frames collected over 54 min | 30 sec exposure time each | f/4 | ISO 3200 | 14 mm

Second image

Date and time: July 6, 2019 | 2:35 – 3:16 local time

Sky and foreground frames: 78 frames collected over 41 min | 30 sec exposure time each | f/4 | ISO 3200 | 14 mm

I took this long exposure after crossing underneath the Elbe River through the old tunnel. One can see the Landungsbrücken ferry port, and the Bernhard Nocht Institute for Tropical Medicine on the left. Just behind it is the Reeperbahn in Sankt Pauli. The Big Dipper asterism of Ursa Major is visible in the sky. Located in the handle of the Big Dipper, one can differentiate by naked eye, between the two stars of a double-star system: Mizar and Alcor— also known as the horse and the rider. 

TECHNICAL DETAILS

Location: Old Elbe Tunnel viewpoint, Hamburg, Germany (φ 53°32'32.6"N, λ 9°58'02.3"E)
Date and time: September 13, 2012, 1:36 local time
Sky and foreground frames: A single frame | 15 sec | 16 mm (cropped) | f/8 | ISO 100
Camera and lens: Nikon D7000 | Nikon AF-S DX NIKKOR 16-85 mm 1:3,5-5,6G ED VR

This was the first attempt at imaging the Milky Way with my new full-frame camera setup. For this image, I used an ultra-wide-angle lens, which I had rented specifically for this purpose. This allowed me to capture a large portion of the Milky Way, using a fairly long exposure.

Thunderstorms can be seen in the distance, in addition to lights from surrounding towns and cities. Also visible are several light trails from airplanes.

TECHNICAL DETAILS

Location: Dead Horse Point State Park, Utah (φ 38°28'14.2"N, λ 109°44'33.6"W)
Date and time: July 1, 2019, 0:18 local time
Sky and foreground frames: A single frame | 30 sec | 14 mm | f/4 | ISO 800
Camera and lens: Nikon Z6 | Nikon NIKKOR Z 14-30mm f/4 S