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ISS observation

I have been made by a friend to point out how beautiful the see International Space Station (ISS) in the evening sky. There is always a period of 14 days in which it is good to see, then not again for about 10 days. If it is not visible in the evening, she takes her "grinding" at this hour just on the southern hemisphere.

By day you can see the ISS, since the sky is too bright. At night, the ISS is flying in the shadow of the earth as it is not illuminated and can not be seen as well. Only if it is just dark with us and the ISS is still lit by the sun, she appears very bright. Brighter than all the other stars and satellites of the planet can only Venus be brighter if it is cheap.  Man kann die ISS meist einige Minuten sehen, bis sie entweder am Horizont wieder verschwindet oder aber irgendwo mitten am Himmel innerhalb von wenigen Sekunden unsichtbar wird, wenn sie dort in den Schatten der Erde eintritt. - This is worth seeing, especially if you know the reasons!

on a Web page, the overflights appear each evening visibility for the next ten days (by clicking on "more" and another 10 days)
www.heavens-above.com/PassSummary.aspx ? satid = 25 544 & lat = 48.30494 & lng = & loc = 14.28944 & alt = 720 Linz & tz = PST
because I've given the coordinates of Linz. The can be changed easily, eg by selecting the Google Map below configuration to www.heavens-above.com

One could also observe the ISS in the morning, but that seems in our society (me included) less popular be.

opinion to the ISS: ISS = International Space Station

altitude about 350 km
orbital period about 91 min
orbit between 51.6 ° north and south Paps
dimensions 110 m × 100 m × 30 m (large solar panels!)

The ISS is only in the evening (and morning) for a particular time to see before they disappear in the earth's shadow (or after it emerges from it). This time is surprisingly long. For the ISS's orbit takes about 90 minutes, but it is visible on some days in the evening to a second time. There must be at least 90 minutes last from sunset until the ISS will disappear in the shadows. With a simple drawing and some expect you can understand that.

The ISS is located 350 km above the earth's surface, the Earth's radius is about 6370 km. This is shown in the figure below schematically. For simplicity, we consider an orbit around the equator.

Figure: Sketch of the ISS orbit (dashed circle) around the earth with solar radiation S and observation punk 1, 2 and 3

The sunlight (S) comes from the left and touches the surface at the highest point (position 1) of the ball. When we are at position 1, the sun rises on the horizon as (we assume a flat landscape, can in mountainous areas that look something different). Since the orbit of the ISS is higher (in the drawing as shown exaggerated in order that a resolution is good), it is only in point 2 in the Earth's shadow. The radius of the earth to the highest point is marked and is re a right angle to the grazing ray of sunshine in point 1 The distance from the center of the earth to the ISS is called with the vector and forms re rs and the horizontal solar beam a right-angled triangle. It is re = rs * cos (phi). By inserting the values of re = 6370 km and 6720 km = rs can calculate the angle phi = 18.57 °. (The phi angle in the drawing is about 25 °, since this is not to scale.)

If one is exactly where rs intersects the Earth's surface, so you can see the ISS vertically above when it is immersed in the Earth's shadow . At what point after the sunset, this is the case? For a 360 ° rotation the earth needs 24 hours, how long it takes for the 18.57 °? A simple calculation gives a time of 1 hour and 14 minutes. You can enter the ISS in Earth's shadow but also see even further to the right, namely, to where the light touches the Earth, the ISS tangential. This is illustrated in Section 3 of Fig. As you can see from the sketch of section 3 but is seen by two straight symmetrical to point 1, ie a further 18.57 ° angle. The date on which an observer at point 3, the ISS on the horizon at rising already sees the Earth and disappear is then twice as late as in point 2, ie 2 h 28 min after sunset (as it is seen not really). But you can with the ISS at least under favorable conditions see more than 2 hours after sunset in the sky before disappearing into the Earth's shadow. I

this bill for one lap and one observation was carried out along the equator, but I do not consider how this changes in other latitudes.

Links:
www.heavens-above.com
www.marco-peuschel.de/Beobachtung ISS
www.isstracker.com
de.wikipedia.org / wiki / ISS