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Recently, I visited the NASA website which provides sighting locations to see the International Space Station (ISS). As we all know, we can even see ISS with the naked eye in a clear sky as a passing star without any blinking.

But unfortunately, I don't know how to measure the angle on the sky to see it. On the official NASA website there's given height (altitude) and direction as 21° and 11 above N respectively.

Here is the link: NASA - Spot The Station

How do I trace ISS?

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The ISS is very bright. As long as you are looking in roughly the right area of the sky at the right time you will see it. For reference, the width between your thumb and pinky stretched apart at arms length is about 25 degrees. You'd need a pretty unobstructed view to be able to see things at this height. Best to wait for times when the ISS is more than 45 degrees above the horizon at its maximum altitude. –  dgh Feb 25 at 7:57
    
Where should i start stretching my thumb and pinky apart at arms length when ISS is about 25 degrees in the sky. –  Praveen Kadambari Feb 25 at 8:06
    
There are lots of apps (if you have a smartphone) that alert you when the ISS is going to be visible at your location. They show you the path is going to take, and therefore what direction you need to look at. For example: play.google.com/store/apps/… –  Electrosa Feb 25 at 11:28
    
@Praveen Kadambari, you start at the approx compass direction provided. Eg if the ISS will appear at 15 above NE, look to the NE, hold your hand out, spreading your index and pinky fingers apart. Put your pinky on the horizon. When you look at your index finger it will be around about 15 degrees above NE. See my answer below... –  Jeremy Mar 6 at 8:43
    
@Jeremy I have seen ISS yesterday and felt amazing .. –  Praveen Kadambari Mar 10 at 16:46

1 Answer 1

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The official site you point to has 3 pieces of location information: 1) the max height angle 2) the point it appears 3) the point it disappears The only one of these that is especially accurate is the max height angle, and that isn't the number you want to use to try and see it. However, passes with a bigger number for the max height angle will be easier to see.

To find the ISS, get the reference to the point it "Appears" - that is the "11 above N" you have described. Now, notice that the reference to the compass direction is simply N or NNE or SW or whatever. This is not a precise directional reference, but it doesn't need to be, as if you're looking towards that direction, you shouldn't have any problem seeing ISS appear. It isn't clear to me if the website is using True North or Magnetic North for the direction; Magnetic North might be easier for people with a simple compass to find, but usually these directions will be relative to True North, which is not where a compass points. From a quick check using my own location, it appears that they have used True North, which is maybe a bit unfortunate. If you don't know where True North is for your location, you can look it up, and then you have to remember to adjust the reading off your compass by the offset for your location.

Notice that the description is "11 above N". This means 11 degrees above the N direction. The reason for it appearing some distance above the horizon is because it is coming up out of the shadow of the Earth, which is being cast some distance above the horizon.

To quickly and easily estimate angular distances, use the trick of observing your hand at arms length. Different parts give different angular dimensions. It is a pretty fair estimate, because no matter how big or small you are, the relative size of your hands and the length of your arms is probably about the same as everyone else... not good enough to use as a survey instrument, but good enough to guesstimate locations on the sky.

The second position description is the "Disappears" location. That is where the ISS will again drop into the shadow of the Earth. Similarly, it is described as degrees above a True North compass direction.

You can figure out (approx) the path the ISS will take by drawing an imaginary line between these two points. However, don't draw that imaginary line so it goes over your head, note the "Max Height" angle again: this is the highest point on the line that you draw between the "Appears" and "Disappears" spots.

Just give it a go, especially one with a pass that starts around 30mins or so after sunset, and that has a high "Max Height" angle. It won't be hard to see.

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