Since Russia launched Sputnik 1 into low Earth orbit in 1957, thousands of satellites have begun congesting the skies over our planet – something anyone shooting night-sky timelapses will be keenly aware of.
Having spent much of the past five years doing just that, I started considering ways to create a timelapse composite that showcased these satellite trails.
Here I’ll run through the steps I took to make ‘Big Brother is Watching You’, my highly commended image in the People and Space category of 2024’s Astronomy Photographer of the Year competition.
I captured the frames for this image in the early evening. Satellites are most visible a few hours before sunset and after sunrise, when the Sun is low enough to darken the skies, but at an angle that its light strikes the satellites.
This timelapse comprised one hour of six-second exposures at f/1.4 and ISO 5000.
Before creating the timelapse, I batch-edited the frames in Adobe Lightroom.
To do this, I headed to the Develop module and edited a single frame to my liking.
I chose to increase the prominence of each satellite by moving the Contrast, Whites and Dehaze sliders to the right, and then decreased Shadows, Blacks and Highlights.
To apply that to all of my frames, I then selected all remaining frames (Ctrl + A) and synced the settings (Ctrl + Shift + S > check all settings > Synchronize). I then saved the frames as ‘Satellite images’, ready for Photoshop.
In Lightroom, I also chose a background image for the composite and edited it as desired before saving it separately as ‘Background image’.
When editing this frame, I made sure the empty sky was lighter than the sky in the satellite images, to make compositing the satellites with the background image easier.
Next, I loaded the ‘Satellite images’ as a stack in Photoshop (click File > Scripts > Load files into stack > select files), with Layers set to ‘Lighten’ (see image below).
I then merged the layers into groups of five by selecting five layers at a time before right-clicking and selecting ‘Merge Layers’, which reduced the number of layers from 515 to 103.
Each satellite then appeared as a streak of five lines, making them easier to find (see image below).
Mask the layers
It was then time to select and separate out the satellites in each layer using masks, so that they could be combined with the background image.
To do this, I first ‘deactivated’ all layers except the bottom one, by unchecking the eye symbol next to the others.
To make it obvious which satellites I was masking, I used a pink-coloured layer (click Layers > New Fill Layer > Solid Color > select pink) before clicking the ‘mask’ icon (highlighted, image below).
The pink layer simplifies this masking process by clearly showing the masked satellites.
Using the Brush tool, I carefully masked out each satellite streak by clicking and dragging the brush over each individual streak (image below).
Once done, I inverted the mask by clicking the mask icon and pressing Ctrl + I simultaneously – this masks everything except the satellites in that layer.
Using this method is much easier than attempting to mask out everything other than the satellites using the Brush tool.
I repeated this for the rest of my layers by clicking and dragging the pink layer to the layer above, clicking its eye symbol to reactivate it, and then clicking the mask icon again (image below).
Once all the layers were masked, I deleted the pink fill layer and changed all layers to ‘Lighten’ again.
To complete the composite, I loaded the background image at the bottom of the stack by clicking File > Open > selecting File > Ctrl + C > Ctrl + V and click-dragging it to the bottom of the layer stack.
The brighter sky of the background image helped conceal any masking artefacts around each satellite streak. To finish, I made final edits using the Camera Raw Filter (Filter > Camera Raw Filter).
While this process doesn’t account for variations in satellite visibility resulting from the time of year and atmospheric conditions, I find that it creates a beautifully arresting image.
3 quick tips
- Use short exposures (2.5–6 seconds), a wide aperture (around f/1.4) and a high ISO (say, ISO 5000) to capture the timelapse.
- Using a bright-coloured fill layer below the active layer will make masking easier.
- For mask adjustments, use the square bracket keys to make your brush size larger or smaller.
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This guide appeared in the August 2025 issue of BBC Sky at Night Magazine