Welcome to SciShow Space News!  I'm Hank Green, and I am psyched because July 19th marks the 45th anniversary of the lunar landing of Apollo 11.  You might've heard about this one.  It was, you know, the giant leap for mankind.

Not only was it the first adventure our species ever took to another world, but it also taught us A LOT.  In just over four hours, Neil Armstrong and Buzz Aldrin traveled hundreds of meters in the dusty lunar soil, collected more than 20kg of samples, and installed equipment that we are still using today.

So in honor of that day, we bring you just four of the most important discoveries made by Apollo 11.

(0:39) Discovery number one: there is no life on the moon.  Remember this is 1969 we're talking about, we'd never been anywhere else but Earth so we truly had no idea of what awaited us and we didn't even know for some time after the Apollo crew returned home.  When Armstrong, Aldrin, and their pilot, Michael Collins, splashed down in the Pacific Ocean, NASA made sure they didn't bring back any tiny hitchhikers with them.

They were bathed in a solution of sodium hypochlorite and then quarantined for 21 days.  Their command module was sanitized and the raft with all the clean up supplies was intentionally sunk to the bottom of the ocean.  But after extensive testing of the soil and rock samples the astronauts brought back, it turned out there was no sign of life.

The materials were totally inorganic and at the time, it seemed like there was not even any water.  Actually, though, there was water.

Scientists assumed that the traces of water they detected in the samples were the result of contamination because there was so little of it and because they didn't find any minerals that form in the presence of water.

Well we now know that there is a trace amount of water, we remain fairly sure that there is no life on the moon.

(1:42) Number two!  The moon is more like Earth than we thought.

Before Apollo 11 we had no idea what the moon even was.  Was it a chunk of space rock that had been captured by Earth's gravity like Mars' moons are?  Or was it a piece of the earth that had broken off?

We're still not totally sure but we've learned how to read the clues thanks to Buzz and Neil.

Among the equipment they planted on the moon was a seismometer, which measured and transmitted data back to Earth about moon-quakes.  By studying the seismic waves from these quakes at various depths, we found out that the moon has layers. Much like Earth, there was a crust, a mantle and a core, composed of materials much like earth's only depleted in iron. And the rocks and dirt that Apollo crew brought back also told us about the moon's geologic history. Namely the sample shows that moon rock share the same distinct ratios of oxygen isotopes as earth rocks, suggesting they have a common origin. So, thanks to Apollo 11, we now have the giant impact theory. A model that suggests 4.5 billion years ago, a giant body collided with Earth, and broke off the chunk that became the moon, and tared not to love number 3.

(2:46) Einstein, as he so often is, was right. Early in the 20th century, Albert Einstein proposed the strong equivalence principle. This posited, in very basic terms, that all forms of matters accelerated at the same rate in response to gravity. So by extension, even thought they're very different sizes and compositions, both earth and the moon would be drawn toward the sun at the same rate. To prove this, Einstein calculated the exact orbit of the moon. But from Earth, we weren't able to measure it precisely enough. Then, Apollo 11 installed the lunar laser ranging array, a panel of 100 small mirrors. By aiming a laser from Earth at this array and recording the time it took to reflect back, astronomers were able to measure, for the first time, the exact distance between the Earth and the moon.
It turned out, the moon's orbit was the same shape and size predicted by Einstein to within one millimeter. And, to this day, we still use that array to study the moon's orbit. 

(3:40) And finally, maybe the most inspiring thing that Apollo 11 taught us, was just: "We can do it!" and in a technological sense, we were never sure that we could send humans to another planetary body, until we just did it. To do it, we had to invent things like, the first computer to use large-scale integrated circuits or chips, we had to develop a renewable efficient fuel source known as the fuel cell, and I'm not even talking about heat shields and dehydrated foods and cordless tools any of the other countless patent-able inventions that went into that historic mission.

(4:10) So if you're as excited about the landings anniversary as we are, and say so, Buzz Aldrin himself is celebrating the occasion here on YouTube, and asking you to share your memories, thoughts and inspirations concerning landing. 
So if you'd like to take part, watch this or upload a video and include the hashtag #Apollo45 in the title or description. 

(4:28) Thanks, as always for watching SciShow Space news. If you want to keep exploring the universe with us, check out subbable.com/scishow, to learn how you can help support us. And don't forget to go to YouTube.com/scishowspace and subscribe.