05 September 2006

Astronomy update

I was out satellite hunting again and I wanted to point out the interesting phenomenon that allows us to actually see satellites at night. As you can see from the image below, the International Space Station was over the Arabian peninsula. The solid line represents the path over the Earth where the ISS would be illuminated by the sun, while the dashed line represents the time when the Earth blocks sunlight to the ISS and it is not illuminated. Because the ISS is (currently) 343 km above the surface of the Earth, it is illuminated for a longer period of time even when the surface of the Earth below is dark. Thus, while the sun has set in Greece in the globe below, the ISS could see be seen over Iraq. This allows us to see objects, depending on their altitude, for about 2 hours after sunset and two hours before sunrise.
The next picture below is a closeup of the globe above. As you can see on the chart, at approximately 21:07, the ISS passed out of the sun's illumination. This is interesting to watch, as well. You might think that the bright ISS moving across the sky just disappears, but it does not. The intensity of the ISS begins to fade until you can't see it anymore. This takes place over a period of 15-20 seconds.
The final picture below is a sky chart which helps you to locate the ISS in reference to known star constellations (and in this case, the Moon and Jupiter). Referencing the chart, I saw that the ISS would become visible below Ursa Major (the Big Dipper) and travel just past Arcturus (in the constellation Bootes; Arcturus' magnitude of -0.05 makes it one of the brightest stars in the sky). As Heavens Above says: This chart shows the path of the satellite across the sky. Please note that East and West are NOT the "wrong way round" if you hold the chart over your head to correspond to the view of the sky.
All images are from Heavens Above.
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