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HOWTO: ISS Viewing
outdoors : by Tommy - October 5th 2011, 09:08PM
The fact that there's a space station orbiting above the globe right now has become somewhat passe in pop culture. Not many people are truly wowed at the news of it. Within seconds, a few clicks of a mouse will take you to hundreds of pictures and videos of the International Space Station; but did you know you can see the space station yourself? No binoculars or telescopes needed! I figured I would write up a HOWTO for the uninitiated. It isn't hard, it just takes a little know how.

For starters, you need to know a few terms used when talking about satellites (the ISS is a satellite of the planet Earth).

The first term when dealing with satellites is azimuth. Azimuth is a technical term that means the same thing as heading, bearing or direction. Most people are comfortable with the cardinal directions North, South, East and West. The cardinal directions are fine for general directions, but to know exactly where something is we need to be more specific. When dealing with an azimuth, a number of degrees is stated. 0 is North, 90 is East, 180 is South, 270 is West, and on around to North again. Kinda get the picture? It's a full circle divided into 360 degrees. (Also note, there's technically no such thing as 360 when dealing with Azimuth, because 360 would be the same as North, but that's already 0.)

It's not entirely what you think. Sure altitude means height, but we're not talking in feet or meters here. Remember, we're dealing with observational angles here, so knowing how high something is is of little consequence to us. Altitude in astronomy means "angle above the horizon". Altitude is expressed in degrees, just like azimuth. 0 is at the horizon, 90 is straight up. 45, you guessed it, is right in the middle. Take a second and hold your arm out parallel with the ground. That's 0. With your other arm, point straight up. That's 90. Find 30 and then find 60. Using these angles as references, you'll quickly be able to find a "close-enough" estimation about most any angle of altitude.

See? Not too hard. Now, let's combine the two.
Point of reference
A good starting point for know where the Space Station will approach from is to first find where North is. If you don't already know which way North is, you can use the Big Dipper to find the North Star which is "true north". Once you have North established, turn and face north. Straight ahead is 0. Behind you is 180. To your right is 90, and to your left is 270. (Incidentally, the angular altitude of the north star is your latitude on a map.) Now that you have azimuth figured out, you can add in altitude angles to see that you can quickly pinpoint any position in the sky day or night using these two values.

Finding our target
To be able to track the ISS, we need to know it's current position which is constantly changing as the station is in orbit. (It's moving at ~17,500mph!) Fortunately for us, there are several free websites that provide second-by-second positioning of the ISS. The main website that I use for celestial tracking (and perhaps the easiest to use) is N2YO.com. Open up the ISS link in another window or tab and let's look at the interface. N2YO tries to estimate your position based on your internet provider's geographic data. (Which something to be aware of, so make sure it's pinpointing your location correctly! As long as it's within 30-40mi, that's close enough for causal viewing.)
The N2YO screen should show you a table of information with varying degrees of yellow. The brighter the yellow, the brighter the ISS will be during a pass (known as magnitude. These yellow boxes are not the only times the ISS flies over. In fact, the ISS passes over about once every 90 minutes. (Yep, around the world in 90 minutes.)
To see all of the passes over your location, you can click on the grey button labeled "Show All Passes". Quite a few right? They are not yellow, because you will not be able to see the ISS during those passes. To hide the ones we can't see, click the grey button "Show visible passes only".

Reading the Information
To understand the table, read the columns left to right. The first column shows us the date of the pass along with the time you will first be able to see the ISS as it's coming into view, as denoted by the green UP arrow. (The satellite is said to be rising at that time) Times are expressed in military time. Numbers less than 1200 are morning, numbers greater than 1200 are afternoon/evening. To convert to the "normal time", if the time is greater than 1200, simply subtract 1200 from the number. The number next to time/date is the beginning azimuth. At the time/date stated previous, at the azimuth stated, the ISS will begin flying over your position at 0.
The next column is the highest elevation of the pass, stated with a time and azimuth. Then, finally the end of the pass will be at the time and azimuth in the last column. Using this information and your newfound understanding of azimuth and elevation, you should be able to string along the three key points of the pass to determine the general direction of the entire pass (just connect the dots).
Oh, yeah, a note on brightness. In astronomy, brightness is referred to as magnitude, as stated previously. The lower the magnitude, the brighter the object. The greater the magnitude, the dimmer the object.
I also suggest trying to spot the ISS on a clear night with little or no cloud cover, as few visual obstructions as possible, and pick a pass where the maximum altitude is greater than 45 and magnitude is -1.0 or lower. You may be able to see it lower altitude or higher magnitude passes, but you may easily miss it on the lower, fainter passes.

So, what am I looking for?
Phew! - you made it. Hopefully, I haven't scared you off. It really isn't as complicated as it may sound and you'll soon discover that casual viewing of the entire pass does not require you to pin point and measure angles. Once you see it, you'll be able to visually track the brightest and highest flying spacecraft ever. So what will it look like? The ISS will look like a quickly moving star. At times it'll be the brightest object in the night sky, flying very quickly. You'll know it's not a plane because its light does not blink. It also may appear to be going much faster than any plane flying so high up.
Those with binoculars might be able to barely make out the outline of the shape of the ISS as it passes directly over your position (>70 passes).

I hope you've found this helpful, I'll gladly update to clarify anything that may be confusing. Clear skies!

Reference: N2YO - ISS link

tags: iss space astronomy satellite howto

+ Grendel
  Oct 05, 2011 21:43
Q: Why is it so small?
A: The ISS isn't small, but it is 200miles away (at the very closest, directly overhead.) The very fact you can see it at all is quite astounding when you think about it.

Q: Why is it lit up on some passes?
A: It's not light from the ISS you're seeing. It's actually sunlight being reflected off of the mondo solar panels that power the ISS. At certain times of the day, the angle of the sun is just right to reflect off of the ISS and onto a point on the ground. (Similar to using a mirror or your watch face to reflect a beam of light at someone.) Sometimes you're in the path of that "glint" from the sun. Thus, you can see the ISS illuminated by the sun. As soon as that angle is no longer optimal, the ISS fades from view before it even sinks below the horizon.


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