NASA recently published an amazing image (Fig. 1), showing the Moon, our only natural satellite, and the International Station (ISS), Earth’s largest artificial satellite, passing close to the Moon. This photograph, taken from Houston, Texas, records a magnificent alignment of Earth’s two largest satellites.
The ISS, the largest spacecraft ever flown into space, is about 109 m wide, and weighs approximately 450 tonnes. It orbits Earth once every 91 minutes, at an altitude of about 350 km. The Moon (3,476 km across) orbits Earth every 27.3 days, at an average distance of approximately 384,000 km, about 1,000 times more distant than the ISS.
In Fig. 1, the most prominent lunar surface features are the bright highlands, known as terrae, the dark lowlands, called the maria (Latin for seas), and the impact craters, which resulted from the collisions of meteorites with the Moon. Interestingly, the ISS appears to be close to the Moon’s surface, in the image, but this is just a matter of perspective, since the two satellites are visible in the same direction.
The ISS can frequently be viewed from Earth’s surface, with the unaided eye, as a bright star rapidly traversing the sky. Intriguingly, the ISS has even been photographed from Earth transiting a more dramatic backdrop, the Sun. It was visible as a dark spot, passing in front of the Sun. PSC Senior Astronomy Specialist, Aymen Ibrahem, has photographed the ISS, on many occasions. In some of Ibrahem’s photos, the Bibliotheca Alexandrina appears as a foreground object.
References
NASA’s Earth Observatory
http://earthobservatory.nasa.gov/IOTD/view.php?id=76942
Wikipedia