Starlink Satellites, 04 January -
15 June 2020
Starlink is a group of thousands of satellites being deployed by SpaceX into low Earth orbit to provide broadband Internet access. A test flight took place in February 2018 and deployment began, in groups of 60, referred to as constellations, in May 2019. Because of the test flight, the launch number is one greater than the constellation number, thus the second launch group deployed constellation Starlink 1, and so on. Below, observations are grouped by constellation.
Constellation 1, Nigel Evans, 04 January 2020
The first constellation of 60 Starlink satellites, launched on 11 November 2019, was well-placed for observation in early January 2020. The night of 04 January was clear with a first quarter Moon, but not particularly transparent. Most satellites of the constellation passed virtually overhead. I was able to record 41 of them, including three slightly out-of-plane with the main group, along with several other satellites that passed through the field-of-view (and two aircraft).
In the animation below, the Starlink satellites pass from 2 o'clock to 8 o'clock. Most were invisible to the naked eye in the moonlit sky, but two were very very prominent, with brightness similar to the stars in Cassiopeia.
Constellation 3, Nigel Evans, 12 & 19 February and 16 March 2020
By mid-February 2020, satellites from the third Starlink constellation, launched on 29 January 2020, had come to visibility in the mornings. The morning of 12 February, although very cold, presented an opportunity to image the objects. The satellites came out of the Earth's shadow at an altitude of about 20°, close to the Moon. The main group consisted of 31 satellites, all in a line with a typical spacing of about 12 seconds. It was possible to see at least 10 satellites at the same time - the sight of them moving as one relative to the stellar background was quite surreal! Towards the end of the pass, one of the satellites was moving visibly faster than the others and overtook another. Currently, most of the satellites are in a circular orbit at an altitude of about 340 km, orbiting the Earth 15.75 times a day, climbing towards an operational altitude of 500-550 km. Starlink 1179 is in a lower orbit of 279x291 km, circling the Earth 15.95 times a day, so appearing to travel 1.3% faster.
I videod the passage of the satellites through the border of Corona Borealis - Serpens. Equipment used: Sony A7S camera, driven, 100 mm telephoto lens at f/2, ISO 16,000. Some acceleration of the event was necessary to reduce the size of the video file. The satellites are nominally in the same orbit, but from the rotating Earth they appear to sweep through a band of the sky. The impact of the satellites on astronomy, flashing through the fields-of-view of telescopes around the word, remains to be seen.
On the morning of 19 February it was again clear and I took the opportunity to record the passage virtually overhead of the constellation. I used a fish-eye lens. Although the satellites are launched in groups of 60 into a low earth orbit, they start to spread out as they propel themselves into their working orbits at an altitude of 550 km. On 19 February, the main group contained 28 satellites that passed in about 8 minutes. The movie below captures most of the satellites from approximately 05:40:30 to 05:49:50 UT. The still frame, taken at 05:47:11 UT shows 14 satellites. Equipment used: Canon 60Da camera, 8 mm fish-eye lens f/4, ISO 3200, 2 s exposures.
On 16 March, there was an opportunity to catch a train of satellites from constellation 3 passing directly overhead. Forty of the 60 satellites passed over in a group, one every 25-27 seconds or so, with eight visible at any one time. At this time the objects were mainly in an intermediate circular orbit at an altitude of 380 km.
The video below was taken using a driven mount. The evening sky was not particularly clear, with cirrus cloud present. Again I used a fish-eye lens, which meant that aircraft were a major problem, and removing them from the video was tedious!
Constellation 4, Nigel Evans, 12 March 2020
The morning of 12 March was not very clear, the Moon was up and it was very, very windy, but it was the first opportunity to observe constellation 4, launched on 17 February. The main pack (about 44 satellites out of 60) passed by in 18 minutes. They were mostly 25-27 seconds apart, not as close as some earlier launch groups have been, but it was still possible to see six or more at once. All bar one could be identified using predictions from heavens-above.com: the exceptional one moved like all the others but there was no associated prediction. All the satellites passed close to the star Pherkad (γ Ursae Minoris, magnitude 3.05) which most of them matched in brightness.
I normally use a driven mount when recording Starlink satellites, but I forgot to switch it on initially! As a result, the stacked composite near the beginning of the video shows star trails.
Constellation 4, Mike Whybray, 21 April 2020
My video of the passage of constellation 4 on 21 April is below. The two brightest stars in the lower left are Castor and Pollux. The video starts at 21:00 BST. It is cropped and resampled from a sequence of full frame images taken with a Canon 550D using a Samyang 14 mm lens at F4, 2 s exposures.
Constellation 5, Nigel Evans, 07, 19, 20 & 21 April 2020
On 07 April, I finally saw the Starlink satellites belonging to constellation 5. Conditions were mixed: the atmosphere was cool, calm, silent and still, but the sky was hazy and moonlit with cirrus clouds. I set a camera running, taking images to make a time-lapse movie. I had initially intended to set up a second camera in video mode, but concluded that conditions did not warrant it.
Usually, with the camera running, I watch the satellites pass overhead, but this time I could not see them. Nevertheless, the camera recorded them together with some additional "features" including a large brightness gradient across the field of view and moving cirrus clouds. (I have removed the gradient in the second part of the video, to give a much more pleasing appearance.)
I don't know why the satellites were so faint. Towards the end of the video, Starlink 80 (from constellation 1) can be seen passing above the path of the satellites from constellation 5, and appearing much brighter. Curiously, heavens-above.com does not include magnitude estimates for constellation 5, whereas it does for all the others.
By 19 April, heavens-above.com was providing magnitude estimates for constellation 5, indicating that the satellites would be exceptionally bright. I recorded the passage that night, half expecting another disappointment. Unfortunately, I was late in starting, so missed the first few satellites. I was stunned by how bright the satellites appeared, some appearing roughly as bright as Regulus.
The video below has not been polished - I have not removed the aircraft, nor labelled the satellites.
The passage of constellation 5 on 20 April was much different; in fact it was a disappointment! I recorded the passage, using exposures of two seconds, rather than four seconds used on 19 April, other details being the same. In the 20 minute interval from 22:00 - 22:20 BST, some 42 satellites passed through Ursa Major but a video shows only seven and a multiple exposure only 10.
The passage on 21 April occurred during evening twilight. This made it tricky to record because of the variation in background light level as night fell, necessitating more sophisticated processing of the images than had previously proved necessary! In the video below, the left hand pane is a view of the sky as night falls: it is difficult to see the satellites as the Sun is only 9° below the horizon. (However, dust on the sensor is very clear!) The image was captured using a fish-eye lens with a very wide field of view, showing a wide variation in brightness across the sky. The right hand pane shows the sequence of differences between each frame and a running nine-frame median, highlighting moving objects against a much flatter background.
Constellation 6, Nigel Evans, 22 April - 15 May 2020
The launch of constellation 6 was unexpectedly moved forward to 20:30:30 BST on 22 April 2020. This provided an excellent opportunity to witness the first pass of the carrier rocket in the evening twilight, some 20 minutes after lift-off. As the satellites are released some 15 minutes after launch, they were expected not to have separated sufficiently from the rocket to be individually visible.
I imaged the passage with a 600 mm telephoto lens on a tripod with a video head. Predictions for Ipswich showed that the rocket would pass close to Venus, providing a bright marker in the evening sky. Having found the rocket next to Venus, it came closer and rose to higher and higher altitude making it harder and harder to keep in the field-of-view. As it passed nearly overhead at an altitude of 74°, I could no longer follow it.
It's difficult to obtain good results tracking a moving object with a long telephoto lens and, indeed, the rocket appears to dance all over the frame. So I have picked through the video, keeping all the frames where the image is reasonably still, then centred them manually, and turned them into a video. Unfortunately, the time difference between frames is not fixed!
The video shows initially two Starlink objects, a long one and a point below and to the right and, much further to the right, Venus. The point is the carrier rocket. The long streak is a stack of 60 satellites, not individually resolved, after being released by the launch rocket. As they come closer the odd stars fly by from the top of the frame. Near the satellites some stray objects start to flash into view - they are retention rods that held the satellites in place on the carrier. The stack of satellites appears to rotate, but this is an effect of perspective as they pass overhead. Then I lose them before finding them again. By now the stack of satellites and the carrier are back-lit and have become one object again due to foreshortening, but four retention rods are clearly seen as separate items.
Below the video is a composite of selected frames, showing the evolution of the Starlink train as it passed overhead.
Opportunities were initially limited to see the constellation 6 once it had been placed into orbit. However, an opportunity arose in the evening twilight of 24 April. Visually, I could not see anything, but a video showed a train of satellites low down in the south-west. The video below is a 7 s clip of the original recording, cropped 50% both horizontally and vertically. The lower pane is a contrast-stretched version of the original (cropped): the satellites are still somewhat hard to see. The upper pane is a sequence of differences between individual frames and a running median of nine frames.
I then applied further processing to individual frames of the video, all 1500 of them, to produce the still images below the video. The upper still is a sum of individual frames, showing a trail effect, with the satellites following one another through the sky. The lower still is a stack of 25 frames (one second's worth) aligned on the satellites. (The fact that they are moving at slightly different rates makes it not possible to achieve good results stacking a larger number of frames.) It shows 36 distinct satellites, with one or two looking like unresolved multiples. This aligns with the fact that the 60 satellites of the constellation have separated into a group of approximately 40 followed about a minute later by another of approximately 20.
There was another opportunity to observe constellation 6 on 15 June. Some 40 satellites appeared in a regular procession with an interval of almost exactly 20 seconds. They were visible to the naked eye; this contrasted with constellation 7 which was visible earlier in the evening, but required use of binoculars (see below). In part, this was because the satellites of constellation 6 were at an orbital altitude of ~500 km compared to ~700 km for constellation 7. While most of the satellites become visible within the frame, there are a few times (26, 28 and 30 seconds into the video) where the satellites flare at the right-hand edge of the frame. (Unfortunately, the right-hand edge is marred by an ugly green colouration, an artefact of compressing the video from 1080 to 720.)
Constellation 7, Nigel Evans, 05-15 June 2020
Constellation 7 was launched early on 04 June and there were four passages of the satellites over the UK during the hours of darkness on the night of 05-06 June. Unfortunately, conditions were not ideal, with a full Moon, at low altitude in Scorpius, causing considerable glare in the south.
The first passage was in the early evening with the Sun only 8° below the horizon. I could see no satellites, either by naked-eye or in binoculars. I captured with a video camera a series of moving faint dots, as well as a couple of satellites that brightened to magnitude 3 or so. The spectacle was unimpressive.
The second passage was at much higher altitude, up to 80°, in a dark sky. There was not a lot to see, until one satellite appeared at magnitude approximately 0.5. Binoculars then revealed a very impressive train of faint moving dots; however, they were not visible to the naked eye. Light pollution from Ipswich and sky conditions combined to produce a limiting magnitude of approximately four. The resulting video is below: it shows 54 distinct bodies, as a well as a couple that look like unresolved multiples. By way of comparison, Alcor is magnitude 3.96.
The third passage was early in the morning of 06 June, again at high altitude, up to 75°. The sky did not look as clear as before. Again there was a prominent bright satellite, but the rest were binocular objects.
The fourth and final passage was in the morning twilight, with the added complication that the view was towards the full Moon. Several satellites were visible to the naked eye at magnitude one or thereabouts, but most could be seen only with binoculars.
In response to concerns from the astronomical community, SpaceX has introduced a policy of orienting the satellites en route to their operational orbits so as to minimise their impact on the night sky. See https://www.spacex.com/updates/starlink-update-04-28-2020/.
By 15 June, the satellites had spread out and appeared low down in the south-west after sunset. They were visible only with binoculars, not to the naked eye. I recorded 52 in less than 10 minutes, sometimes two or three appearing in the field of view at a time. Later that evening, there was was a passage of the constellation 6 train - details above.
I generally use orbital elements, loaded into a planetarium program, to identify individual satellites. However as the satellites are climbing to working altitude, the elements rapidly become out of date. I found that two sets of data gave a different order to the satellites. Indeed, if the predictions show satellites to be, say, only one second apart, confidence is low that the order is correct. So in labelling the satellites in the videos I follow Eric Morecambe's stance on his interpretation of Grieg's piano concerto for Andre Previn "These are all the right satellites - but not necessarily in the right order!" (Morecambe and Wise Christmas Show, 1971).
Constellation 7, Mike Whybray, 05 June 2020
I captured the second passage of constellation 7 on 05 June starting at approximately 22:45 UT. I used a 135 mm telephoto lens at f4 on a Canon 550D in video mode under pretty clear skies. I recorded the video as 1920x1080 px then rotated and cropped it to 1080x720 px. heavens-above.com predicted that all satellites would appear in the range of magnitudes 1.8 to 2.2. However, in practice they appeared fainter than this so I increased the brightness and contrast of the video to make them more apparent; in consequence, it is rather grainy.
The video is below. The two stars on the left are Mizar and Alcor in Ursa Major (magnitudes 2.23 and 3.99 respectively) and the video gives a good impression of the naked eye brightnesses that I observed - all but one satellite were rather dimmer than Alcor and the bright one was considerably brighter than Mizar. I could barely see the satellites by naked eye but they looked very impressive (almost a space armada!) in binoculars. I tried matching the timings on heavens-above.com with my video but couldn't obtain a good correspondence, so can only identify the bright satellite as around number 40 in the passage. (Satellite 20 in the sequence is tagged on heavens-above as a Visorsat model, i.e. it has a special sun-shield to help avoid reflections from the antenna.)
I expect that the majority of satellites were dimmer than predicted due to efforts by SpaceX to reduce visibility of the craft by angling them during the ascent phase to reduce reflection. Perhaps something went wrong with the bright one?