Can you spot the nine reconnaissance spacecraft in this long exposure of the night sky? These images from "Invisible: Covert Operations and Classified Landscapes" by Trevor Paglen, track the progress of various classified spacecraft in Earth's orbit.

Paglen was able to identify and photograph these secret spacecraft due to the work of a diverse international group of amateur astronomers who maintain a catalogue of classified spacecraft in Earth's orbit by producing mathematical descriptions of orbits using simple tools like stopwatches and binoculars.

Paglen shot these photographs with a host of cameras and telescopes using a computer-guided mechanical mount for accurate "pointing", and to compensate for the rotation of Earth. When you see the satellite as a line against a background of stars, it is due to the object's motion in the sky during a long exposure. When you see the satellite as a bright pinpoint or short line against a backdrop of star trails, you are seeing a geostationary spacecraft. You'll see several examples in this gallery, titled with their curious appellations.

Nine Reconnaissance Satellites over the Sonora Pass, 2008
This is a four-hour exposure of the northern sky over the Sierra Nevada. Visible are at least ten reconnaissance satellites, nine of which are American and Russian. Additionally you can see a number of airplane trails distinguished by dotted paths. 

All images courtesy Trevor Paglen/Aperture

DMSP 5B/F4 from Pyramid Lake Indian Reservation

(Military Meteorological Satellite; 1973-054A), 2009

LACROSSE/ONYX V near Cepheus

(Synthetic Aperture Radar Reconnaissance Satellite; USA 182), 2008 

KEYHOLD/IMPROVED CRYSTAL near Scorpio

(Optical Reconnaissance Satellite; USA 129), 2007 

Four Geostationary Satellites Above the Sierra Nevada, 2007