The position that the ISS will be in the sky changes every night. You can’t watch the ISS pass over during the middle of the day because in the daytime the sky is too bright (although some people with specialized equipment have seen it) and you cannot see the space station in the middle of the night, as it is in the Earth’s shadow and no light is being reflected from it. The light we see from the ISS is reflected sunlight. Not only can you see the ISS in the evening but you can also see it in the mornings as both the ISS and Sun are in the ideal position to illuminate the spacecraft at this time. ISS long exposure photograph over Donnington Castle UK Credit: The International Space Station usually takes around 90 minutes to orbit our planet, so if you’re really lucky you can get two, or maybe even three or four passes in an evening or morning. Short passes can last a few seconds to a few minutes and you can see the international space station slowly move into the Earth’s shadow, good bright passes will show the ISS moving across the sky from horizon to horizon. However, the ISS has no flashing lights and it can be much brighter. The ISS looks like an incredibly bright, fast-moving star and can be mistaken for an aircraft. An average good pass can last about 5 minutes. When the station passes over it will travel from a westerly direction, heading in an easterly direction. Check apps and websites for where and what track the ISS will take on each individual pass. If the ISS will be first be seen 40 degrees above the horizon, look four fist-lengths above the horizon. If you aren’t sure about where to look, a good rule of thumb is that your fist outstretched at arm’s length is 10 degrees. For example, if the maximum elevation is listed as somewhere between 74-90 degrees above the horizon, the ISS will be passing almost straight overhead (Just like you learned in geometry, 90 degrees would be straight up).
Also included are the highest altitude the ISS will be. Most of the apps or websites will tell you what direction in the sky the pass will start and end and how many degrees above the horizon the starting and ending points are. It can be low on the horizon for some passes and very high others. The International Space Station always passes over starting from a westerly part of the sky, but not always from the same point.
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