In the following image (coming from SAT-Flare) you can see the orbit of the ISS (in red) and the day/night terminator (in blue). The terminator separates night from day along the surface of the Earth. @TidalWave recently found that the orbit of the ISS was close to being aligned with the day/night terminator, making for some really nice images. How often will the ISS orbit align with the terminator? When it does so, how long will such an alignment last? And lastly, can it align any closer than it does in this image?