The Pale Blue Dot

01
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The Solar System from Deep Space

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The Voyager 1 "family portrait" taken from well outside the orbit of Pluto. NASA/JPL-Caltech

Imagine you're an interstellar traveler heading toward our Sun. Perhaps you're following the trail of radio signals emanating from somewhere near the Sun, from one of the inner planets of this yellow star. You know that planets with life probably orbit in the Sun's habitable zone, and the signals tell you that there's some sort of intelligent life. As you get closer, you start looking for that planet. And, from a distance of 6 billion kilometers, you spot a tiny blue dot.  That's it, the planet you're looking for. It's called Earth (by its inhabitants). If you're lucky, you might also see the other planets of the solar system, arrayed in their orbits around the Sun.

What you're seeing here is an actual image of all the planets of our solar system taken by the Voyager 1 spacecraft on February 14, 1990. It's called the solar system "family portrait" and was first dreamed up as a possible "long shot" by the late astronomer Dr. Carl Sagan. He was one of the scientists closely associated with the mission, and was responsible (along with many others) for the creation of the Voyager Record. It is a record containing the digital records of sounds and images from Earth, and there is one copy affixed to Voyager 1 and its sister ship Voyager 2.  

02
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How Voyager 1 Looked to Earth

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In 1990, Voyager 1 took the famous "Pale Blue Dot" picture looking back at Earth. In 2013, the Very Long Baseline Array got the reverse-angle shot — this radio telescope image showing the signal of the spacecraft as a similar point of light. NRAO/AUI/NSF

In an interesting "turnabout", in 2013 (23 years after the Pale Blue Dot image was taken by Voyager), astronomers used the Very Large Baseline Array of radio telescopes to "look out" at Voyager 1 and capture its radio signal in a "reverse angle" shot. What the telescopes detected was emission of radio signals from the spacecraft. This blue dot is what you could see if you had sensitive radio detectors and could "see" this tiny spacecraft for yourself. 

03
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The Little Spacecraft That Still Doing It

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An artist's concept of Voyager 1 on its way out of the solar system. NASA/JPL-Caltech

Voyager 1 was originally launched on September 5, 1977, and sent to explore the planets Jupiter and Saturn. It did a close flyby of Jupiter on March 5, 1979. and then passed by Saturn on November 12, 1980.  During those two encounters, the spacecraft returned the first-ever "close up" images and data from the two planets and their largest moons.

After its Jupiter and Saturn fly-bys, Voyager 1 began its trip out of the solar system. It's currently in its Interstellar Mission phase, sending back data about the environments it has passed through. Its primary mission now is to let astronomers know when it has passed beyond the boundary of the solar system. 

04
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Voyager's Position When it Snapped the Shot

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Where Voyager 1 was when it took the image. The green ellipse is the approximate region where the spacecraft was thought to be. NASA/JPL-Caltech

Voyager 1 was well beyond the orbit of the dwarf planet Pluto (which was explored in 2015 by the New Horizons mission) when it was commanded to turn its cameras inward toward the Sun for one last look toward the planet where it was built. The space probe is considered to have "officially" left the heliopause. However, it hasn't yet left the solar system.

Voyager 1 is now on its way to interstellar space. Now that it appears to have crossed the heliopause, it will traverse the Oort Cloud, which stretches about 25 percent of the distance to the next nearest star, Alpha Centauri. Once it leaves the Oort Cloud, Voyager 1 will truly be in interstellar space, which it will travel through during the rest of its trip. 

05
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Earth: The Pale Blue Dot

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That tiny blue dot with the circle around it is Earth as Voyager 1 saw it from beyond the orbit of Pluto. NASA/JPL-Caltech

Earth was a small, blue dot in the family portrait that Voyager 1 returned. Earth's image, now nicknamed "The Pale Blue Dot" (from the title of a book by the late astronomer Dr. Carl Sagan), shows in a very profound way, just how small and insignificant our planet is against the backdrop of space. As he wrote, that contained the whole of life's existence on the planet. 

If explorers from another world ever make their way to our solar system, this is what our planet will look like to them. Will other worlds, abundant with life and water, look like this to human explorers as they seek to find habitable worlds around other stars?  

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Petersen, Carolyn Collins. "The Pale Blue Dot." ThoughtCo, Dec. 3, 2017, thoughtco.com/the-pale-blue-dot-3072350. Petersen, Carolyn Collins. (2017, December 3). The Pale Blue Dot. Retrieved from https://www.thoughtco.com/the-pale-blue-dot-3072350 Petersen, Carolyn Collins. "The Pale Blue Dot." ThoughtCo. https://www.thoughtco.com/the-pale-blue-dot-3072350 (accessed January 21, 2018).