Pictures of the International Space Station

ISS and the Progress freighter ISS and the ATV-4 ISS and the Space Shuttle

Here we have the ISS on the descending part of its path, just before 6pm on the evening of 8th February 2008. The bright object to bottom-right is the planet Mars. The ISS passing through the Hyades open cluster, which sits between Orion and the Pleiades, on 10th February. The brightest star is Aldebaran, the eye of the bull in the constellation of Taurus.

In my description of the visibility of the ISS I mention that it could pass into the Earth's shadow before disappearing over the horizon - here we see it doing just that on 10th February (just moments after the above-right image). The bright star to top right is Betelgeuse in Orion. The trail gradually fades away because, due to scattering by the atmosphere, the edge of the Earth's shadow is not sharp. The enlarged, enhanced, image on the right shows this well.

The first three images above were all published on the SpaceWeather.com website on 11th February - fame at last! However, while recording the track of the ISS during a time-exposure, they don't give a feel for how it really looks so I also tried to get some moving images. This is a much more difficult problem, as the exposure must be a lot shorter with a movie so only the brightest objects will appear. I did have some success though, so here are two movies - one of the ISS passing Mars (as in the first image above, though on the next evening) and a compilation giving the story of an entire pass across the sky, which shows well the changes in speed and brightness during a pass. The movies are quite small, so don't be worried about download times!

ISS and Mars Compilation

It must of course be said that one trail eventually looks much like another, so here are a few "unusual" images.

If the timings are right, it is possible to see more than one ISS pass in a night. Not all will be equally bright or cover an equal arc in the sky, however, due to the changing orientation of the orbit track with respect to the observer. Having seen a bright high-altitude pass one evening I decided to see if I could spot a faint, short, low pass later on. I thus pointed the camera in the right direction at the right time and took a series of 8sec exposures at 400ASA to see what came out. Remarkably, something did - on one frame, anyway! It was definitely the ISS, being in exactly the correct position, caught just after leaving the cloud-bank to the right and just before going into eclipse. If you can't see it, click or tap on the picture to enhance the trail. The brighter of the two stars to top left is Bellatrix (in Orion) while that to top right is Aldebaran. The trees and telegraph poles show how low the pass was - only about 10deg above the horizon.

While most passes are in a dark sky, bright passes early in the evening can be observed while the sky is still blue. For this image, I took snaphots of just ¹/8sec at 50ASA, as a time exposure would simply result in a blank overexposed frame. I then created a composite to show how the ISS slows down as it approaches the horizon (because at this point it is mainly going away from the observer, not across their line of sight). Due to having to re-align the camera, the intervals are not equal but I think it still shows the effect. From top to bottom we have 12sec, 10sec and then three lots of 6sec: it is clear that the distance travelled in the last 6secs is much less than half that traversed in the first 12secs.

While preparing the images for the above composite I was surprised to find that the ISS was not just a "blob" but had a definite shape in each one! The "film strip" below shows a magnified version of each ISS.

The question is, what are these shapes? Are they artefacts of some sort or do they really show actual elements of the ISS? Intrigued, I repeated the experiment on another [less bright] pass. In order to get the clearest results I opened up the lens to its maximum (200mm), increased the pixel resolution of the images, and decreased the exposure time to ¹/20sec by going up to 200ASA. The results are shown below, at the same scaling as the first set (the actual shapes are about 9 pixels by 5).

Several things are clear from these images:- 1) they are all about the same size [and set 1 is similar to set 2 despite the different exposure times]; 2) they have different orientations; 3) they mostly do not lie along the direction of travel [which was about 10deg off vertical in the first case and 30deg upward in the second]. These observations would seem to rule out the possibility that they are simply "mini-trails", and I did what I could to avoid the images being distorted due to camera shake by setting it to take an exposure 2sec after I pressed the button (when my hands would be well clear). Any vibration from wind is also unlikely because, as far as I remember, the air was still on both occasions. The enigma thus remained - a few calculations were clearly necessary!

At a nominal distance from the camera to the ISS of 800km (greater than its orbit height of 400km as it was not directly above me), a structure 100metres wide, such as both the solar arrays and the main "spine", will have an extent of about 26 seconds of arc. With the camera set to 50.8mm true focal length (giving a "film camera equivalent" of 200mm), its theoretical resolution at f3.5 is about 10 seconds of arc. In principle, the camera optics would thus be capable of resolving detail on an object the size of the ISS (under perfect conditions, anyway!). Secondly, given that the field-of-view at 200mm is about 10deg and there were about 3200 pixels across the full image, a perfectly-captured 26 arc-sec object would be 2 or 3 pixels across. However! Things are rarely perfect as I found when taking a series of pictures of Mars to demonstrate its motion across the sky. Even corrected for movement during the time exposure, a 9 arc-sec disc was 5 pixels across and a 16 arc-sec disc was 7 pixels across. This "image spread" is due to many factors, which probably include over-exposure, imprecision of focus, movement of the subject, atmospheric turbulence, peculiarities of the sensor and image coding. Most of these factors will be applicable in the case of the ISS so a "practical" 26 arc-sec image will be considerably larger than the theoretical size. In fact, the images captured are quite a bit smaller than might be expected from the Mars images, probably due to a more correct exposure.

So, we have two sets of objects that are (plausibly) about the size one would expect for objects the size (and indeed shape) of those constituting the ISS. But are they that? Not sure, really! It would be nice to think one is seeing structure but with so few pixels involved it's impossible to be certain - the enigma may have to remain just that!

It's interesting to do the same calculation for the human eye. At its minimum distance of 400km, the ISS subtends a little over 50 seconds of arc. In perfect conditions, the eye can determine that a well-illuminated object is a "non-point" source if it is greater than about 0.7 arc-min, or 42 arc-sec. This is the reason that when you look at the ISS passing almost directly above you it is clearly not just a bright star. However, any impression you may get of "shape" or "structure" is an artefact generated by the eye. It could be due to the flare produced when any bright light is seen against a dark background, or (depending on your level of dark-adaptation) to the eye effectively taking a time-exposure: it can integrate for up to 15 seconds in very low light. This can produce the impression of a small "trail" behind the fast-moving ISS which can be wrongly interpreted as structural detail.

And finally.

With the end of the viewing window approaching I was keen to get a last "decorative" shot - I think this one qualifies nicely. Here we have the ISS in transit across Orion, just above the sky glow (in Wroxham, in fact - yes, another rehearsal night!). The three stars of Orion's belt lie below the centre of the trail, and the bright star at the top is Betelgeuse. Exposure was 30secs at 100ASA and the image was taken on 8th April 2008.

After taking the flurry of images shown above I haven't particularly bothered with getting further pictures, as they do all tend to be rather similar. Also, as the ISS is now very bright there is really no difficulty in photographing it and so the "technical challenge" aspect is not there any more. I have instead tried to capture images of the spacecraft which visit the ISS, as that is much more difficult! The results of my efforts can be seen in the following sections.

ISS and the Progress freighter

When viewing a pass of the ISS in early July 2009 I was very surprised to see it apparently being followed by another satellite. This was not listed on the Heavens Above website but the next day reports came in that it was in fact Progress-M 02M, a Russian cargo freighter. These regularly dock with the ISS to deliver supplies and take away waste but are not usually seen as they do not linger close to the ISS on normal missions. On this occasion, NASA was using the craft for docking tests prior to the arrival of STS Endeavour and so it flew in formation with the ISS for several days.

These images were taken on 10th July and show the ISS (left) and Progress (right) passing just below the bright star Vega. Their tracks are very nearly the same, but not quite - look carefully at their positions relative to nearby stars. The separation between the two craft was 72sec at this time, with ISS leading, meaning I was not able to capture them both on the same image without using an unreasonably wide-angle lens.

Just two days later the two craft had closed to within seconds of each other and so a single shot of both of them was quite possible. Clouds attempted to thwart my attempts to capture them but just failed - pity they weren't a little further to the right, however! In this image [at half the magnification of those above] Progress is just visible on the left, with ISS much clearer to the right: Vega is again to the top of the frame. The exposure was 15sec, and I managed to get the alignment just about perfect so managed to capture the full track of each craft over this period, enabling me to calculate that Progress was now 19sec ahead of ISS. It de-orbited very soon afterwards, burning up as it fell into the Pacific Ocean.

ISS and the ATV

During the last few days of March 2008 the first European Automated Transfer Vehicle, known as 'Jules Verne', performed practice docking manoeuvres with the ISS. This meant its orbit was very similar to that of the ISS, giving opportunities to see them close together in the sky. Taking some of those opportunities proved harder than anticipated, however!

On the evening of 30th March the ATV was orbiting a couple of minutes behind the ISS, "station keeping" in preparation for a close approach the next day. This was also the first time the ISS had been visible in the evening in the UK for several weeks so I was keen to capture the pair. Unfortunately, I was at a dinner party that evening so could only dash outside briefly for a couple of "grab shots" - the other diners thought I was mad! I managed to get these images though, which show the slowly-rising ISS almost occulting Rigel, with the sword and belt of Orion above, (left) and the ATV passing close to Procyon (right). Exposures were 15sec at 200ASA.

After the docking practice on 31st March (which I watched live on NASA web-TV) the ATV pulled ahead of the ISS. Unfortunately, come the evening I didn't know how much in front it was, and I was at a singing rehearsal anyway! I thus had to sneak off and point the camera skywards more in hope than expectation. The ISS came into view right on time but I hadn't seen the ATV so pressed the shutter anyway. A short while later I suddenly saw it some way ahead of the ISS but could do little as the 30sec exposure was already running. Despite swinging the camera round in an attempt to get a second shot after the first exposure had finished, the ATV soon went into eclipse and that was that. Disaster! Or so I thought - when closely examining the image afterwards I found that the ATV had just been in the frame when I pressed the shutter. Oh joy! Thus here we have, simultaneously, a very short trail from the ATV at top left and a much longer one from the ISS: the bright object to mid-right is the planet Mars. From the distance between the start of the trails I could estimate that the ATV was about 18sec ahead of the ISS.

The two were still in close proximity on April 1st but, naturally, I was not at home during the evening (!) so again had to engineer a photo-opportunity. Once more I was taken by surprise by the ATV but contrived to abort the initial exposure by (accidentally!) turning the camera off. Frantic re-alignment was followed by a 30sec exposure while peering hopefully into the sky to persuade myself the camera was pointed in about the right direction to catch at least something. An initial look at the image was not encouraging but detailed examination showed that, as the image on the left demonstrates, I could hardly have contrived things better: I can only assume I was riding a lucky streak! The ATV starts below the middle of the frame and moves off to top left while the ISS appears from bottom right a little later. Based on the overlap of the tracks & the exposure time I calculated that the ATV was now about 24sec ahead of the ISS. It's clear that the trails are parallel to each other (as the two craft are flying at the same angle to the equator [51.6deg]) but because they are in slightly different orbits the tracks don't actually coincide. The bright object to top left is Mars again, by the way: note its movement away from the nearby star compared to the 31st March image.

By April 2nd the ATV had dropped over 2mins behind the ISS again, making it less likely one would be taken by surprise! Unfortunately, cloud decided to enter the equation which meant I could only get a clear shot when the spacecraft were in descent, moving slowly very near the eastern horizon. This image is a composite of individual 15sec exposures, at 100ASA to avoid them being washed out by a still not dark sky. Even so, considerable enhancement was needed to bring out the ATV trail sufficiently, hence the very blue appearance. The orbit tracks seem to have almost come together, but this is simply an effect caused by the Earth's rotation in the time between the individual passes. The bright star to the right of the image is Vindemiatrix, in the constellation of Virgo, while that close to the ISS trail is the beautifully-named Diadem in Coma Berenices.

ATV 'Jules Verne' performed a successful automatic docking with the ISS on 3rd April and separated again on 5th September. Unfortunately, in the UK the ISS was only visible just before dawn then (not my favourite part of the day!) and so I wasn't able to get any pictures at that time. It did come into view in the evenings later in the month so I was able to observe it for the last time before it burnt up in the Earth's atmosphere over the Pacific ocean at 13:46 GMT on 29th September. The composite image on the left shows the ATV (above) orbiting 16mins behind the ISS (below) in the twilight on 27th September. I managed to completely foul up the exposure setting for the ATV unfortunately (hence the poor quality image) but it's definitely there! The bright star between the ATV and the tree is Scheat, the "top right" star in the well-known square of stars in the constellation Pegasus.

ATV-4 'Albert Einstein'

After the success of the first ATV, further craft were launched: ATV-2 'Johannes Kepler' in February 2011 and ATV-3 'Edoardo Amaldi' in March 2012. I was unable to see either, unfortunately, as they were in orbit at times when the ISS was not visible at night from the UK. I had better luck with ATV-4 'Albert Einstein' in June 2013 though, despite the best efforts of the British weather to cloud me out!

I was able to photograph ATV-4 on 6th June, the day after it was launched, during a period when both it and the ISS were performing bright passes high in the sky. This was quite important because (as in the case of 'Jules Verne') ATV-4 is much less bright than the ISS and so is more difficult to catch with the camera. Having taken a test image of the ISS on the pass before the ATV was expected I was firstly able to capture 'Albert Einstein' just over an hour later and then the ISS on its next pass after a further half-hour. All three images had the vehicles passing close to the bright star Vega, which made a good target when aligning the camera.

On the left is 'Albert Einstein', on the right we have the ISS: Vega is the brightest (top-right) of the four stars forming a "7" pattern to the upper-left-centre of the images. The exposure was 15sec at 200ASA in both cases, showing that a) ATV-4, being much smaller, is far less bright than the ISS (mag -0.1 as compared to -3.4), and b) ATV-4 was orbiting considerably faster than the ISS: this is because it was (at that time) about 150 miles high rather than the 250 miles of the ISS.

I was able to observe ATV-4 several times over the following days but did not try to photograph it as the result would have been little different from the images above. At this stage of ATV development there was no need to further practice docking manoeuvres which meant that instead of ATV-4 flying alongside the ISS for an extended period (as was the case for ATV-1) its orbit was just slowly raised to set it up for a docking on 15th June. They were thus quite close together only on 14th June but unfortunately it was totally clouded-out here then so I couldn't observe them. I could perhaps claim to have seen ATV-4 on the day it docked, but as it was attached to the ISS at the time I suppose that doesn't really count!

ISS and the Space Shuttle

As mentioned on the introductory page, despite the many missions flown seeing one of the Shuttle fleet was quite unusual. We were lucky at the end of March 2009 though, as Discovery undocked from the ISS at the end of mission STS-119 and flew close by during a favourable viewing window. It was (of course!) cloudy for one night so when viewing became possible, Discovery was orbiting about 40sec ahead of the ISS. As the longest time-exposure possible with the camera I use is 30sec, this meant that it would not be possible to capture them both in the same frame without using a wide-angle view (which would give a fairly undramatic shot). I thus opted for two separate shots as they passed in sequence through the upper part of the constellation of Orion. Even this was not a straightforward process though, as there still would not be enough time for a full "side-to-side" trail because the camera takes about as long to process an image (i.e. remove noise from a time exposure) and store it as it does to expose it. Add in the 2sec delay I set from shutter press to exposure (to eliminate camera shake) and the timing gets a bit tight! I worked out that if I set the field of view correctly I could press the shutter just before the Shuttle entered the frame, take a 15sec exposure that would have it crossing most of the frame, and still have just enough time for a shot of the ISS before it got too far across. Amazingly, everything worked perfectly!

Here we have Discovery, moving from right to left at 8pm on 26th March. As mentioned above, I had to truncate the shot before it crossed the entire frame so the point where the trail stops is simply the end of the exposure, not Discovery going into eclipse. The slight fluctuations in brightness are due to some light cloud, not anything connected with the Space Shuttle. And 37sec later we have the ISS, noticeably brighter than Discovery (as one would expect). The prominent star close to the trail at top left is Betelgeuse, which marks Orion the Hunter's left shoulder (from his point of view) as he is usually portrayed with his back to the viewer. The slightly less bright star to bottom right is Bellatrix, marking his right shoulder, with the cluster to top right indicating his head. The well-known swordbelt is some distance off to the bottom left.

The two vehicles were physically quite close at this time, so their orbits were very close to identical. This is shown by these composites: the left-hand one simply overlays the trails but the second has the trails coloured red (Discovery) and blue (ISS) first. There is a difference, but it's pretty slight!

The sight of the two very bright "stars" following each other so closely across the sky was a wondrous vision I shall long remember. Their separation was over 1min the following evening, and the pass was in much brighter skies so was not so impressive. I took a video of them as they descended onto the eastern horizon but with the camera in portrait format to capture more of the descent. What I forgot, of course, was that it is much easier to rotate a still than a movie!! However, I was later able to carry out the rotation with the excellent Avidemux program so you don't have to turn your head to appreciate it! Discovery appears first, followed by the ISS. The greater brightness of the ISS is very obvious, even through the electronic noise caused by the low light-levels. Click here to see them, and watch out for the large bird taking flight part-way through! [The video is in "real time", incidentally, so there's quite a gap in the middle before the ISS comes into view. It's also quite small, to keep the file size down, so is perhaps best viewed at the 200% setting].

STS-128

By a strange coincidence, Discovery was again flying with the ISS (as mission STS-128) on the next occasion that a Space Shuttle was visible from the UK - only just though, as it was the first bright pass of a new evening "viewing season". On the night of 10th September 2009 Discovery was expected to be 2min ahead of the ISS, on almost exactly the same track and at mag -0.9 but in fact was none of those! The gap was nearly 3mins, the track was much further south and the brightness was maybe as low as +3.0 - all indications that STS-128 was in a much lower orbit than predicted. This was entirely reasonable though, as it was scheduled to make its de-orbit burn just 2hrs later and so had presumably been lowering its orbit in preparation - bad weather at the landing site prevented this, however.

Not a particularly "pretty" image, admittedly, due to the large amount of contrast enhancement needed to bring out Discovery's faint track before the two images were combined. The aircraft which decided to join in the party and produce a line of dots didn't help either! The bright star to top middle is Altair, in the constellation Aquila.

Note that the lower orbit has caused Discovery to enter eclipse much sooner than ISS: the abrupt start of its trail at the right was simply because I had to press the shutter "by eye" as the Shuttle was earlier than expected - I was a bit late, however!

STS-129

The next shuttle mission was undertaken by Atlantis, which I observed briefly while it was on its way to dock with the ISS but did not attempt to photograph as the visible part of its track was short and low to the horizon. The docked pair were then seen on a number of occasions during bright passes on subsequent days, but as the evening viewing window was coming to an end I thought that would be it for a while. But no! The very last visible pass was during the early evening of the day when Atlantis undocked. A quick check on the orbit parameters showed that the two should still be very close indeed when passing over me, and so it turned out.

I had lined up my camera well in advance just in case I could capture a "double pass" so was able to get a lovely shot of them gliding from right to left just below the planet Jupiter, low in the south.These images were taken at 5:13pm on 25th November 2009 and show the ISS leading Atlantis. The separation in time was so short (just 4¹/2sec) that I was easily able to capture both of them with a single exposure - 15sec in this case. Atlantis was much fainter than the ISS (and both were not particularly bright due to the low elevation) so the visual effect was not as dramatic as the double pass of ISS and Discovery described above, but the proximity of the two made up for this. It really was amazing to see the two dots closely tracking each other across the sky (like a man being followed by his dog!).

The right-hand image is an enlargement of the trails, a portion of which can be further enlarged by clicking or tapping within it. This shows that the tracks are nearly, but not quite, the same - that of Atlantis is just above that of the ISS. This is because Atlantis was in a slightly higher orbit than the ISS at the time (about 1km): maybe not what one might have expected. To an observer on the ground, the higher orbit will appear to be further north ("upwards"), as shown in the image. The higher orbit will also have a fractionally greater orbital period (if only by a few seconds), thus explaining why Atlantis was trailing the ISS. The physical separation was about 15mls at this time.

And that, of course, is the last we shall ever see of the Space Shuttle fleet - the last mission to fly was Atlantis on STS-135, launched on 8th July 2011 and landing on the 21st. Craft still fly to the ISS of course, but none so dramatic as the Shuttle.

Back


Here we have the ISS on the descending part of its path, just before 6pm on the evening of 8th February 2008. The bright object to bottom-right is the planet Mars.	The ISS passing through the Hyades open cluster, which sits between Orion and the Pleiades, on 10th February. The brightest star is Aldebaran, the eye of the bull in the constellation of Taurus.

In my description of the visibility of the ISS I mention that it could pass into the Earth's shadow before disappearing over the horizon - here we see it doing just that on 10th February (just moments after the above-right image). The bright star to top right is Betelgeuse in Orion. The trail gradually fades away because, due to scattering by the atmosphere, the edge of the Earth's shadow is not sharp. The enlarged, enhanced, image on the right shows this well.

	If the timings are right, it is possible to see more than one ISS pass in a night. Not all will be equally bright or cover an equal arc in the sky, however, due to the changing orientation of the orbit track with respect to the observer. Having seen a bright high-altitude pass one evening I decided to see if I could spot a faint, short, low pass later on. I thus pointed the camera in the right direction at the right time and took a series of 8sec exposures at 400ASA to see what came out. Remarkably, something did - on one frame, anyway! It was definitely the ISS, being in exactly the correct position, caught just after leaving the cloud-bank to the right and just before going into eclipse. If you can't see it, click or tap on the picture to enhance the trail. The brighter of the two stars to top left is Bellatrix (in Orion) while that to top right is Aldebaran. The trees and telegraph poles show how low the pass was - only about 10deg above the horizon.
While most passes are in a dark sky, bright passes early in the evening can be observed while the sky is still blue. For this image, I took snaphots of just ¹/8sec at 50ASA, as a time exposure would simply result in a blank overexposed frame. I then created a composite to show how the ISS slows down as it approaches the horizon (because at this point it is mainly going away from the observer, not across their line of sight). Due to having to re-align the camera, the intervals are not equal but I think it still shows the effect. From top to bottom we have 12sec, 10sec and then three lots of 6sec: it is clear that the distance travelled in the last 6secs is much less than half that traversed in the first 12secs.
While preparing the images for the above composite I was surprised to find that the ISS was not just a "blob" but had a definite shape in each one! The "film strip" below shows a magnified version of each ISS. The question is, what are these shapes? Are they artefacts of some sort or do they really show actual elements of the ISS? Intrigued, I repeated the experiment on another [less bright] pass. In order to get the clearest results I opened up the lens to its maximum (200mm), increased the pixel resolution of the images, and decreased the exposure time to ¹/20sec by going up to 200ASA. The results are shown below, at the same scaling as the first set (the actual shapes are about 9 pixels by 5). Several things are clear from these images:- 1) they are all about the same size [and set 1 is similar to set 2 despite the different exposure times]; 2) they have different orientations; 3) they mostly do not lie along the direction of travel [which was about 10deg off vertical in the first case and 30deg upward in the second]. These observations would seem to rule out the possibility that they are simply "mini-trails", and I did what I could to avoid the images being distorted due to camera shake by setting it to take an exposure 2sec after I pressed the button (when my hands would be well clear). Any vibration from wind is also unlikely because, as far as I remember, the air was still on both occasions. The enigma thus remained - a few calculations were clearly necessary!


These images were taken on 10th July and show the ISS (left) and Progress (right) passing just below the bright star Vega. Their tracks are very nearly the same, but not quite - look carefully at their positions relative to nearby stars. The separation between the two craft was 72sec at this time, with ISS leading, meaning I was not able to capture them both on the same image without using an unreasonably wide-angle lens.
	Just two days later the two craft had closed to within seconds of each other and so a single shot of both of them was quite possible. Clouds attempted to thwart my attempts to capture them but just failed - pity they weren't a little further to the right, however! In this image [at half the magnification of those above] Progress is just visible on the left, with ISS much clearer to the right: Vega is again to the top of the frame. The exposure was 15sec, and I managed to get the alignment just about perfect so managed to capture the full track of each craft over this period, enabling me to calculate that Progress was now 19sec ahead of ISS. It de-orbited very soon afterwards, burning up as it fell into the Pacific Ocean.


On the evening of 30th March the ATV was orbiting a couple of minutes behind the ISS, "station keeping" in preparation for a close approach the next day. This was also the first time the ISS had been visible in the evening in the UK for several weeks so I was keen to capture the pair. Unfortunately, I was at a dinner party that evening so could only dash outside briefly for a couple of "grab shots" - the other diners thought I was mad! I managed to get these images though, which show the slowly-rising ISS almost occulting Rigel, with the sword and belt of Orion above, (left) and the ATV passing close to Procyon (right). Exposures were 15sec at 200ASA.
After the docking practice on 31st March (which I watched live on NASA web-TV) the ATV pulled ahead of the ISS. Unfortunately, come the evening I didn't know how much in front it was, and I was at a singing rehearsal anyway! I thus had to sneak off and point the camera skywards more in hope than expectation. The ISS came into view right on time but I hadn't seen the ATV so pressed the shutter anyway. A short while later I suddenly saw it some way ahead of the ISS but could do little as the 30sec exposure was already running. Despite swinging the camera round in an attempt to get a second shot after the first exposure had finished, the ATV soon went into eclipse and that was that. Disaster! Or so I thought - when closely examining the image afterwards I found that the ATV had just been in the frame when I pressed the shutter. Oh joy! Thus here we have, simultaneously, a very short trail from the ATV at top left and a much longer one from the ISS: the bright object to mid-right is the planet Mars. From the distance between the start of the trails I could estimate that the ATV was about 18sec ahead of the ISS.
	The two were still in close proximity on April 1st but, naturally, I was not at home during the evening (!) so again had to engineer a photo-opportunity. Once more I was taken by surprise by the ATV but contrived to abort the initial exposure by (accidentally!) turning the camera off. Frantic re-alignment was followed by a 30sec exposure while peering hopefully into the sky to persuade myself the camera was pointed in about the right direction to catch at least something. An initial look at the image was not encouraging but detailed examination showed that, as the image on the left demonstrates, I could hardly have contrived things better: I can only assume I was riding a lucky streak! The ATV starts below the middle of the frame and moves off to top left while the ISS appears from bottom right a little later. Based on the overlap of the tracks & the exposure time I calculated that the ATV was now about 24sec ahead of the ISS. It's clear that the trails are parallel to each other (as the two craft are flying at the same angle to the equator [51.6deg]) but because they are in slightly different orbits the tracks don't actually coincide. The bright object to top left is Mars again, by the way: note its movement away from the nearby star compared to the 31st March image.
By April 2nd the ATV had dropped over 2mins behind the ISS again, making it less likely one would be taken by surprise! Unfortunately, cloud decided to enter the equation which meant I could only get a clear shot when the spacecraft were in descent, moving slowly very near the eastern horizon. This image is a composite of individual 15sec exposures, at 100ASA to avoid them being washed out by a still not dark sky. Even so, considerable enhancement was needed to bring out the ATV trail sufficiently, hence the very blue appearance. The orbit tracks seem to have almost come together, but this is simply an effect caused by the Earth's rotation in the time between the individual passes. The bright star to the right of the image is Vindemiatrix, in the constellation of Virgo, while that close to the ISS trail is the beautifully-named Diadem in Coma Berenices.


Here we have Discovery, moving from right to left at 8pm on 26th March. As mentioned above, I had to truncate the shot before it crossed the entire frame so the point where the trail stops is simply the end of the exposure, not Discovery going into eclipse. The slight fluctuations in brightness are due to some light cloud, not anything connected with the Space Shuttle.	And 37sec later we have the ISS, noticeably brighter than Discovery (as one would expect). The prominent star close to the trail at top left is Betelgeuse, which marks Orion the Hunter's left shoulder (from his point of view) as he is usually portrayed with his back to the viewer. The slightly less bright star to bottom right is Bellatrix, marking his right shoulder, with the cluster to top right indicating his head. The well-known swordbelt is some distance off to the bottom left.

The two vehicles were physically quite close at this time, so their orbits were very close to identical. This is shown by these composites: the left-hand one simply overlays the trails but the second has the trails coloured red (Discovery) and blue (ISS) first. There is a difference, but it's pretty slight!