Has anyone seen this going across recently? Amazing sight, tonight you could also see the supply craft a few seconds behind it. Amazing to think it's flying past at over 17,000 MPH!

If anyone is interested search #ISS on Twitter for more information.

Saw it for about 45 seconds last night.

Serious question . Is it actually moving at 17k mph ? Or is it stationary (ish) and the 17k mph is just in relation to the rotation of Earth

To get into orbit it (or its pieces) needed to attain escape velocity and it retains that movement now. If it didn't it would crash to earth (unless it were in a geo-stationary orbit). I mean, this is the simple answer - but all movement in the universe is relative. Entire books have been written on this very complex question.

Is that a yes? Or a no?

Neither and both.

Galileo was the first to suggest that universe doesn’t care if you are moving or not. He noticed that he got the same results to his experiments if he were stationary or moving at a constant speed (impressive as he was on a boat, the sea must have been very calm). It was common knowledge at the time two people observing an object in motion would disagree on the object’s speed if one of them was moving. Galileo cast doubt on which one of them would be correct. It becomes very difficult to answer the question of how fast an object is moving if you do not have a reference frame in which we can measure all objects speeds. This reference frame is referred to as the absolute reference frame. Such a reference frame requires the very fabric of the universe to be full of a substance called luminiferous aether through which all objects move in time, and therefore the speed of any object could be obtained.

In 18887 Albert Michelson and Edward Morley performed a famous experiment which showed the absence of luminiferous aether. There is no absolute frame of reference. The result proves that there is no difference between an object being stationary and moving at a constant speed. Any object that is not accelerating (physicist called this an inertial frame of reference) no matter how fast it is moving is actually stationary. You can only quote a speed relative to another frame of reference, and therefore you can pretty much quote any value you wish and you will find a frame where this value holds true. Added to this, all inertial frames are equal in this theory, and the universe can’t tell the difference. Einstein used the Michelson Morley result in his paper "Zur Elektrodynamik bewegter Körper" ("On the Electrodynamics of Moving Bodies"icon_wink.gif, better known as special relativity. The year was 1905, his Annus Mirabilis.

If you have ever tried to dink a cup of tea in a moving car you will notice that when the car is not accelerating it’s easy. This reminds me of trying to do my homework on the bus on the way to school, bloody thing kept starting and stopping, it was nearly impossible. On an airplane it’s easy to do pretty much anything (space permitting), my three year old daughter on a recent flight to Lanzarote looked out of the window at the clouds below and said ‘Daddy we’re not moving’ I didn’t take the time to explain to her that she was indeed correct.

Most of the time all of this is meaningless because we live on a massive planet that will always try to return us to the same speed as it. Or more correctly, to zero miles per hour relative to the point on the surface that we are. When we quote the speed of an object it tends to be relative to the surface of the Earth. For all situations in most people’s lives the Earth is the absolute reference frame. Although most would be aware that the measurement of a year uses the Sun as its absolute reference frame. It is the inability to mentally let go of the surface as a frame of reference that make the ideas so alien.

17,000 mph? I suspect, but don’t know, that this figure is arrived at by taking the of the Earth as the of the space station’s orbit, calculating the circumference and then dividing it by period of the orbit. Interestingly if you do the same for a person on the surface of the Earth, the speed varies from 1000 mph at the equator to zero at the poles. As I mentioned earlier most of the time we would measure speeds relative to ourselves being stationary. This makes no sense for a satellite as the shape of its orbit would be incredibly complicated and its speed would be constantly changing.

Simple! Except none of the frames of reference mentioned are inertial fames.

Could only happen in The Sin Bin .

So . To simplify .
Is it actually flying at 17k mph around Earth ? Yes or no .

If Earth stopped rotating would the thing in space continue zooming around in orbit ? Yes or no .

Or ... Would it be stationary above one place ? Yes or no .

Its tied by a very fine but very strong and very long fishing twine tethered to a railing outside the offices of Lockheed Martin in Maryland, occasionally people forget when they want to use the railing to tie bedsheets with "Happy 40th Chuck" written in felt tip, and they'll accidently release said satellite twine which result in it soaring off into space never to be seen again, such satellites being filled with helium - its at those times when one or more Sky channels tend to disappear to be replaced a few weeks later by ones that are more s[ihi[/it simply because they've had to buy space on someone else's satellite.

It's clearly not in geostationary orbit and its use would be limited if it was.

If you were on it you'd be doing the above speed.
Relative speed to something else may be different.
Relative to the centre of the Earth it would be doing 17,227 miles per hour.
The Earths surface is itself moving at around 1,000 miles per hour relative to it's centre.

Spot on again Mr Field. Professor Brian Cox must be quaking in his boots!

Can we not just ask them to look at the speedometer?

This sounds like Stevo's momentum rule.

If a Saints player moving at 17000 mph throws a 'flat ball' which is 16999 mph moving forwards, is it a forward pass

I am out every night its passes, most evening lately have resulted in the cloud ruining any chance. Was out for the metor shower last night also, only saw one , boo hoo.... Love the ISS, blows my mind when I see it pass over us. It only takes 2 minutes to cover the length of the UK, and doesnt pay the M6 Toll either !

Only at the equator. The speed tails off down to zero as you move towards either pole, so the speed of the ISS relative to an observer on the surface of the Earth will depend on the latitude of the observer.

sometimes i see orange/reddish light,s is that the ISS or is it the one where its extremely brighter than the normal stars??
ta.

True enough.
It just gives an idea of the speed of the ISS.
If the Earth at the equator is going at over 1,000 miles/hr and the ISS is in a lowish orbit and it's doing 15.7 orbits a day and say happened to be orbiting around the equator (for the sake of the fag-packet maths argument), it's not hard to see that it's doing around 17,000 miles an hour.



Fag-packet maths coming up......


4230ish/4000ish (radii of orbits) X 25,000ish/24 (speed of Earth's rotation at equator) X 15.7 = 17,295 ish.
Near enough ...

Best thread for ages this. I've evernoted it.

The easiest way to picture the situation is to imagine that the Earth is a stationary object. The ISS flies at a certain height and the distance it travels in one orbit is the circumference of that circle.

So you know the distance (ie far one orbit is), and you can easily time how long one orbit takes.

And the speed in kph or mph is simply the distance travelled in one orbit, divided by the time it takes.

(In fact the height of the ISS varies between 370-460 km) above the surface of the Earth, and the speed varies between about 7.7-7.6 km per second).

You could make a case for the ISS travelling at vastly different speeds, and it is (for example if you factor in the rotation of the Milky Way, or indeed the speed of the Milky Way) but those factors are not relevant as whatever other components there may be in the motion of the ISS, still in the orbit it is in, it must travel at the speed it does in order to stay in orbit.

Your perspective on Earth isn't important either. If you are on the North Pole then your speed with the rotation of the Earth is nil (you just rotate once every 24 hours as the Earth spins); and if you're on the equator then you are rotating, with the spin of the Earth, at a bit over 1,000 mph. But that's not relevant to you, because in reality we are all stuck at ta point on the surface of the Earth, and what speed our rotational component is, makes no difference to us.

What you are seeing is probably Mars, the other stationary bright light is Venus (or the Moon

) The ISS is a white light but is moving across from West to East at quite a speed.

So .. Earth is rotating at 1k MPH ( I understand the 1 rotation per day equals 1k MPH at the surface ) and it suddenly stopped turning , anyone stood on the Equator would continue moving forwards at that speed . Ouch .
If Earth ceased rotating the ISS would continue travelling round in orbit at a speed of 17k MPH (ish) ?
Oooh ! That brings more questions . If Earth is rotating at such a high speed (at the equator )how do aeroplanes manage to move in both directions around it ? It would make sense that you only have to get yourself clear of the ground and stay static to have Earth move underneath you . You could be a thousand miles away from your start point in an hour . But it doesn't work like that does it . That would mean that a plane travelling in the opposite direction at over a thousand miles an hour to make any progress at all . I assume that it is possible for this scenario to happen , but at what altitude .
Does the ISS travel in the opposite direction to Earth's rotation to enable such high speeds ? And how is it powered to keep it at that velocity ?


I really should be saving questions like this to amuse myself if ever I were to find myself on a seemingly endless walk . Oh ! *cough* @james2odsal*cough*

Spot the blatant plug

If Earth ceased rotating the ISS would continue travelling round in orbit at a speed of 17k MPH (ish) ?
Would the answer to this one be that it would slow to 16K MPH ?

I sense you are taking the mickey.

The same speed would be require to stay in orbit, but a boost would be required to compensate for the gravitational drag caused by the stopping of rotation.


Irrelevant. Planes only have a velocity in forward flight RELATIVE TO THE EARTH. Thus wherever they take off from, they only CHANGE their speed relative to the surface.


You can't "stay static". You have to travel faster than the Earth's rotation (how much faster depending how high you are) to appear to hover over the same spot.

In space a geostationary orbit is possible in what is called the Clarke belt (after Arthur C. Clarke) and is 35,786 km high.


No, all spacecraft take off in the direction of the Earth's rotation, precisely to take advantage of the boost in speed this offers, and for the same reason, space bases are as near the equator as practicable, as there the Earth is spinning the fastest.

Once the boosters have boosted it into orbit, the ISS has a certain amount of fuel which it uses to regularly raise its orbit, to compensate for the deceleration caused by atmospheric drag.

[url=http://www.nasa.gov/multimedia/nasatv/iss_ustream.htmlWatch them watching you watching them.[/url

Very awesome.