International Space Station


Sightings

Sightings in 2000
Sightings in 2002  
Sightings in 2003  


Progress Report (added 23 Jun 2002)

The ISS is now bigger than my original alert at the end of 2000 as several Space Shuttle visits have added new modules and solar panels. The orbit remains the same as before, so the sighting details in my original alert still hold true, though the increased size means a greater brightness.

Any of the following websites can give predictions as to when you can see the ISS;;;


News Alert (by e-mail on 21 Dec 2000)

A few people have been asking about seeing the new International Space Station and the Daily Telegraph ran an article on 19th Dec. alluding to its presence as a Christmas Star. Certainly it should now be a lot brighter following the addition of solar panels a few weeks ago.

I have therefore done a bit of research and find that, unlike the more usual subject of cosmic updates, this should be an easy object to see at a time that is convenient to everyone. Although of course a clear sky is required, it is less dependent on the weather on any particular day because there will be many opportunities to see it. Indeed, as months and year pass it will get brighter as more modules are added, but it is certainly worth a look for over the festive period so you can be among the first to have seen it.

My research has taken me to the website Lift-Off which runs a program that allows you to track the position of satellites in their orbits around the Earth (J-Track) and make predictions as to what can be seen, and when, from any particular place on the ground (J-Pass). When downloaded it runs as a Java applet in the browser, and is capable of being used offline without the need for a continuous internet connection. You can also request that it sends you e-mails notifying you of the visibility from your chosen location of objects you select, though I haven't tried this yet.

General Aspects of ISS's Visibility

I have run predictions from various parts of the UK for the next 2 weeks and they say that the ISS will indeed be visible most evenings until the end of December. The following ground rules seem to hold true for all sightings, and will be useful to bear in mind when relating my predictions to your location.

a) The ISS passes from west to east, rising between south-west and west and setting between east and south-east.

b) The maximum elevation that it can reach in the sky is as follows, as measured upwards from the southern horizon:-
Exeter: 105 degrees (i.e. 15 degrees north of the zenith)
London: 90 (i.e. directly overhead)
Manchester: 55
Edinburgh: 35
Inverness: too low to be reliably seen
It orbits at about 300km altitude with an orbital inclination of 52 degrees, which means that London is about as far north as you can be to see it overhead. As you go further north, so the maximum elevation drops off as you get further from the track of the orbit.

c) The spread of longitude across the UK makes relatively little difference to rising and setting times because of the high speed at which the ISS is travelling, 17,500 mph = 5 miles a second. For example the distance from Exeter to London of 150 miles (3.5 degrees of longitude) is covered in just 30 seconds, so Exeter's timings are typically 30 seconds ahead of London's. However, as you travel north the lower elevation tends to postpone rising times, in the same way as the winter sun rises later than a summer one. The net result is a difference in rising times compared to London (51.5 degrees N, 0 degrees E) typically as follows:-
Exeter (50.7N, -3.5E): 30 seconds early
Manchester (53.5N, -2.0E): 15 early
Edinburgh (56.0N, -4.0E): 30 early
(I have quoted the longitudes as negative numbers because the program expects it to increase in an easterly direction. Alternatively subtract from 360, so for example Edinburgh can be stated as 356 degrees)

d) The time taken from rising to setting for a most favourable pass (i.e. one that achieves as high an elevation as possible for the location) seems to be fairly constant at 10 minutes for all locations. However, given that the ISS will be harder to see at low elevation (because of greater distance, a thicker amount of atmosphere for the light to pass through, and more likely to be obscured by trees, buildings etc) I have calculated the times to reach 30 degrees elevation, and how long it will remain above 30 degrees, as follows:-
  Time from rising to reach 30 degrees Time above 30 degrees

Exeter

3m 40s 2m 40s

London

3m 40s 2m 40s

Manchester

3m 40s 2m 30s

Edinburgh

4m 10s 1m 20s

These are durations for the best possible passes - for less favourable passes the time spent above 30 degrees will be less, and in Edinburgh could be zero. Nevertheless it does give some indication of how long you have got to make a sighting after the rising times quoted below.

e) At this time of the year (December) most appearances are within 2 hours of sunset or sunrise. This is because in order for it to be visible the sky needs to be dark (i.e. it is nighttime on the ground), but the ISS itself needs to be in daylight as it shines by reflected sunlight. This also means that on a late evening appearance you may see it pass into the Earth's shadow during the course of its passage across the sky, or emerge from it in the early morning. During the summer the hours of visibility are extended as the sun is not so far below the horizon, and in June it looks as if sightings can be made almost throughout the entire night.

f) The brightness is officially stated as magnitude -0.5, which is equivalent to a bright star or Saturn, but less than Venus or Jupiter. However, the solar panels act as mirrors so depending on the relative positions of the sun, the ISS and the observer it is likely that on occasions it will appear much brighter than this. A brightness similar to Venus (i.e. magnitude -4) has been mentioned but only real sightings will determine just how bright it can get.

ISS Visibility in December 2000

I have ascertained appearances of the ISS between now and the end of December as follows, stating rising time and the maximum elevation from each site. If a second time is quoted it is when it passes into the Earth's shadow and you will not be able to follow it all the way to the eastern horizon. On the basis that nobody will be too inclined to get up early in the morning I have given evening appearances only.

Date Time

Max. Elevation (degrees up from S horizon)
My Observations...
December GMT Exeter London Manchester Edinburgh A bit of a dismal record!
Thu 21st 5.33pm 105 90 55 35 Cloudy
Fri 22nd 4.30pm 85 80 50 Too low Cloudy, sky too bright
Sat 23rd 5.02pm 105 90 55 35 Cloudy
Sun 24th 5.35pm 90 70 45 30 Cloudy
Mon 25th 4.32pm 105 85 55 35 Cloudy, sky too bright
Mon 25th 6.07 - 6.13pm 55 40 Too low Too low Cloudy
Tue 26th 5.04pm 85 60 40 Too low Cloudy
Wed 27th 5.36pm 40 30 Too low Too low Saw it for the first time
Thu 28th 4.33pm 70 50 35 Too low Clear, but sky too bright
Fri 29th 5.05pm 35 Too low Too low Too low I was too far north


As December progresses so the orbit gradually shifts day to day making evening appearances less favourable, after which they cease completely until early February. However, in the first 2 weeks of January there will be opportunities to see the Russian
Mir space station instead in the evening. I won't give you the times for these but if you are interested you can have some practice on the predictor program yourself. Alternatively use the J-Pass E-mail facility to have the site automatically e-mail you details of upcoming sightings.

I haven't seen the ISS myself yet owing to inclement weather, so I hope we get some fine evenings over the festive period. Happy hunting and have a good Christmas.



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