On September 5, 1977, NASA’s Voyager 1 spacecraft lifted off from Cape Canaveral, Florida, aboard a Titan-Centaur rocket. Thirty-five years later, the planetary probe is now an interstellar traveler, having traveled farther from Earth than any manmade object in history. As of 21:00 Universal Time on September 4, 2012, Voyager 1 was 18.21 billion kilometers (11.31 billion miles) from home, or 121 times the distance from the Earth to the Sun. Light takes 33 hours and 44 minutes to travel the distance from the Sun to Voyager 1 and back.
The images above were taken at a time when Voyager 1 was much closer to home. The top image of a crescent-shaped Earth and Moon was captured on September 18, 1977, when Voyager was a mere 11.66 million kilometers (7.25 million miles) from Earth and directly above Mount Everest (on the night side of the planet at 25 degrees north latitude).
The lower image and inset—often referred to as “the Pale Blue Dot” image—was acquired on February 14, 1990, when the spacecraft was 6.4 billion kilometers (4 billion miles) from Earth and 32 degrees above the ecliptic plane. Earth is a mere point of light, just 0.12 pixels (picture elements) in size when viewed from that distance. The fuzzy light in the images is scattered sunlight because Earth was very close to the Sun (from the perspective of Voyager). The image was part of a series of 60 images collected to make the first-ever mosaic portrait of our solar system.
Both images were assembled from data from the Imaging Science Subsystem on Voyager 1, a modified version of the slow-scan vidicons used in the Mariner spacecraft and similar to early television cameras. The wide-angle camera had a field of view comparable to a 200 millimeter lens with an aperture of f/3, while the narrow-angle camera had the field of view of a 1500 mm, f/8.5 lens.
Having long since passed its primary targets of Jupiter and Saturn, Voyager 1 has been cruising for decades toward the edge of the solar system. In fact, researchers have analyzed data from the probe’s particle detectors, cosmic ray detectors, and magnetometer and found evidence that they have passed the termination shock and into the heliosheath—the outer edge of influence for solar wind plasma and energy from our Sun. The probe is now in an area similar to the windless “doldrums” found in tropical seas on Earth. The solar wind has calmed, the magnetic field has piled up due to pressure from outside the solar system, and high-energy particles appear to be leaking out into interstellar space. The Voyager science team expects the spacecraft itself to pass out into that space sometime in the next year or so.
“Voyager tells us now that we're in a stagnation region in the outermost layer of the bubble around our solar system,” said Ed Stone, Voyager project scientist at the California Institute of Technology, at a December 2011 press conference. “Voyager is showing that what is outside is pushing back. We shouldn't have long to wait to find out what the space between stars is really like.”
For more information about the spacecraft, visit the Voyager web site at the Jet Propulsion Laboratory.