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I was wondering why low earth orbit satellites can not be seen from the same place all the time? For instance, the ISS passes over my house twice in a month. Why does it happen only two times?

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    $\begingroup$ Related: Can I see the ISS from the surface with the naked eye? $\endgroup$
    – user
    Jan 20, 2015 at 15:23
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    $\begingroup$ Assuming you live at a latitude less than +/- 52 degrees, the ISS will pass over your house (i.e. above the horizon, not necessarily directly overhead) several times per day, not only twice a month. But the lighting conditions for it to be visible may be much less frequent, since that requires your location to be dark but the ISS to still be in sunlight. $\endgroup$
    – pericynthion
    Jan 20, 2015 at 21:42

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The ISS orbits approximately once every 90 minutes. In that 90 minutes, the earth rotates about 15 degrees. Thus, your position under the orbital track of the ISS changes each orbit. Combine that with the ISS' position in its orbit when you are on the ground track and you get the result you are observing.

As mentioned in the comments, inclination matters. If the ISS was orbiting with an inclination of 0 degrees and you lived on the equator, it would pass over you every orbit (every 90 minutes). But, the ISS orbits at about 51 degrees inclination and I suspect you don't live on the equator. The higher the object's inclination, the more you will move under the ground track each orbit.

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    $\begingroup$ Mention inclination. If you were orbiting around the equator, it would be the same. But every degree you angle away from the equator, the more you move. $\endgroup$
    – geoffc
    Jan 20, 2015 at 15:57
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This has to do with orientation of the satellite's orbit. The ISS does not orbit the Earth along its equator, instead it makes an angle of 51.65 degrees with the equator. Like Erik said, it is orbiting faster than the Earth is rotating which means that it passes over a different swath of land every orbit.

So long story short, between the Earth rotating at one speed, the ISS orbiting at another, and the plane inclination of the ISS's orbit, there are a lot of things that have to line up in order for the ISS to pass over your head.

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