Hank Green: Today, on the day that bears his name, we honor a man, and you should be able to tell who that man is just by looking at my outfit.  

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Carl Sagan died almost 17 years ago, so perhaps some of you are unfamiliar with his work and legacy, but if you enjoy the work of Bill Nye, Neil deGrasse Tyson, or even us here at SciShow, if you easily get sucked into the movie Contact, or have ever geeked out over the location of Voyager 1, then Sagan has influenced your life.  Sagan is best remembered as a popularizer.  He brought planetary science to the masses with enthusiasm that stood out in an often dry academic field.  His biographies almost always include phrases like 'man-child' or 'child-like wonder', which, if you've ever seen an episode of Cosmos, makes a lot of sense.  But Sagan was much more than just a face on PBS or The Tonight Show.  

Born in 1934, he grew up in a working class Jewish neighborhood in New York City, and knew from an early age that he wanted to be an astronomer.  In his 20s, first as a grad student at Berkeley, and later while working at the Smithsonian Astrophysical Observatory, he helped solve the climate mystery of Venus.  At the time, many thought Venus had temperatures similar to Earth's, but Sagan studied radio emissions from the planet and determined that they were the result of surface temperatures of over 482 degrees Celsius.  Later, while teaching at Cornell University, he was part of a team that proved color shifts observed on Mars were the result of high winds, not changing seasons.  In the early 1970s, Sagan worked on a NASA team to help choose the landing sites for Viking 1 and 2, which in 1975, would become the first spacecraft to land on Mars.  He was also a member of the NASA group that worked on Voyager 1 and 2 prior to their launches to explore the solar system and beyond.

It was Sagan who proposed including a message from Earth aboard each spacecraft in the event that they were ever discovered by extraterrestrials, the message he helped devise dubbed 'The Golden Record' includes thousands of recordings of sounds from Earth as well as simple illustrations and diagrams of life on our planet.  

Sagan rocketed to worldwide fame in 1980 with Cosmos, the 13 part PBS mini-series and accompanying book.  Both set records for audience and readership in the genre, and his marveling at the vastness of the universe, whether it be stars or atoms numbering in 'billions and billions' became embedded in popular culture.  

Sagan, of course, was not perfect, his stubbornness and obsession with success ruined two marriages and caused periods of estrangement from his children.  He held grudges and could be petty.  He once sued Apple for libel, when, after Sagan told the company they couldn't use his name as a code word for a new computer, Apple engineers instead used the name BHA, for Butt-Head Astronomer.  

But let's focus on the good stuff, like the image that is probably most associated with Sagan, that would be the pale blue dot, the famous photograph of Earth taken by Voyager 1 on February 14, 1990, as it approached the edge of the solar system.  That is what our home looks like from 6 billion km away.  

In one of his final books, Sagan reflected on that image, writing in part, "That's us.  On it, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.  The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every super star, every supreme leader, every saint and sinner in the history of our species lived there, on a mote of dust suspended in a sunbeam."  

Carl Sagan would have been 79 years old today.  Happy Birthday, Carl. 

And thank you for watching this episode of SciShow.  You can find us on Facebook and Twitter, and don't forget to go to YouTube.com/SciShow and subscribe if you want to keep getting smarter with us.  

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