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Tim

Will the space station appear a tiny bit slower now?

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Increasing a circular orbit from 200 miles to 240 miles should make it about 150mph (about 1%) slower, so that should give a rough idea of the effect.

calculated using: sqrt(((6400 + 200) / (6400 + 240))^3) * 17000 = 16847

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It came over last night on a NW/SE orbit, seen it a bit late and tried to get the mount round to it but it was way toooooooo fast ;).

Jim

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We had a clear look at the 2230 ish fly past, brilliant. They must have been busy onboard as they didn't wave back.

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Has anyone managed to image the ISS at all or does it move too quick?

Jonathon.

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Has anyone managed to image the ISS at all or does it move too quick?

Jonathon.

Yes, there are some superb images from telescopes. I don't know the links but there should be someone who does know them ;)

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Yes, there are some superb images from telescopes. I don't know the links but there should be someone who does know them ;)

I would love to see them if anyone knows any links it would be appreciated.

Jonathon.

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As it's clear tomight I thought I'd take a peek with my bins - however Stellarium and Heavens Above disagree about the time -Stellarium says it rises above the Western horizon at about 22.56 - HA says 23.08 - first time they've disagreed - time will tell!

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Full marks to Heavens Above exactly as stated - lovely clear bright pass - Does my Stellarium need an update?

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Full marks to Heavens Above exactly as stated - lovely clear bright pass - Does my Stellarium need an update?

As TJ says in the OP, the station's orbit has just been boosted so you probably just need to update your satellite TLE. My copy of Stellarium was spot on.

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Saw it about 20 minutes ago between clouds and it seemed brighter than Ive ever seen it......nice and slow too.

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Ha d the Bins out tonight to see the ISS - good view as it belted overhead. Really bright the last 2 nights - looks like venus.

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I saw last night's 22:35 pass. It still seems to move pretty fast and hard to tell if it's any slower, but it was the longest ISS observation I've made to date. It was a high pass, culminating a tad under 60 deg, but I was able to follow it for almost 8 minutes, whereas my previous best would be around 6.5 minutes

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I saw the ISS pass just an hour ago at 23:15. I had my 10" out with a 15mm eyepiece. Never hand tracked it before. could clearly make out the solar panels. It was very bright. I did get rather excited. ;)

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Anyone care to calculate the chances of some fisherman out upon the ocean catching the family's next meal being hit by a " robust piece of hardware " ?

;)

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Thanks for posting this link TJ. ;)

Also, those amazing pics by Thierry Legault never cease to amaze me..

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Increasing a circular orbit from 200 miles to 240 miles should make it about 150mph (about 1%) slower, so that should give a rough idea of the effect.

calculated using: sqrt(((6400 + 200) / (6400 + 240))^3) * 17000 = 16847

Two questions.

1) 6400? ;)

2) When we view a moving object in the sky, the speed we perceive is angular speed (inversely proportional to period), not linear speed. For circular orbits, linear speed is proportional to r-1/2, while angular speed is proportional to r-3/2 (which you have used). Why, then, mph?

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Oops. I mixed up some miles and kilometers there! ;)

Not sure if I understand your second point. The idea was to work out the proportional change in speed using p^2 = r^3. Isn't it valid to do that, or did I miss something else?

edit: I guess finding the speed change doesn't tell you how different it will look from here as the height has changed too.

Edited by Dave R

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Not sure if I understand your second point. The idea was to work out the proportional change in speed using p^2 = r^3. Isn't it valid to do that, or did I miss something else?

This gives the answer to TJ's question, but it doesn't directly give the relationship between the new and old speeds.

The apparent visual speed that we see (angular speed) is inversely proportion to the period of orbit (if we lived on a glass Earth, we would see a satellite go around one in a time of one period), so

(visual speed)new / (visual speed)old = pold / pnew = (rold / rnew)3/2

This can be used to give a percentage change in visual speed.

The actual (linear) speed is given by distance over time. In a time of one period p, the satellite orbits once a circle of circumference 2 pi r, so

v = 2 pi r / p.

vnew / vold = (rnew / rold) * (pold / pnew)

Now, (possibly after squaring everything) use Kepler's Law to replace the p's by r's.

For small changes, the percentage change for visual speed should be about three times the percentage change for actual speed.

Sorry for being picky.

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I managed to see it through a break in the clouds from here in Cardiff and although difficult to judge, it seemed to be travelling at the same speed before it was put into it's new orbital height.

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As TJ says in the OP, the station's orbit has just been boosted so you probably just need to update your satellite TLE. My copy of Stellarium was spot on.

Done that now - back to normal!

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