Short Wave - How Venus got caught up in an 18th century space race

Episode Date: November 13, 2023

In the 18th century the world was focused on Venus. Expeditions were launched in pursuit of exact measurements of Venus as it passed between Earth and the Sun. By viewing its journey and location on the Sun's surface, scientists hoped to make a massive leap in scientific knowledge. With a little help from math, Scientist in Residence Regina G. Barber recounts how humanity came closer to understanding our cosmic address — and relative distances to other planets — in the solar system. If you haven't heard the other two episodes in our series on cosmic distances yet, check them out here:- The Stars that Settled The Great Debate- What The Universe Is Doing Right NowWant to get in touch with story ideas or to share some science that delighted you? Email us at [e-mail]!See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Back in the mid-1700s, people were just beginning to figure out the vast scale of the solar system. And thanks to astronomer Johannes Kepler, we've known since the 1600s what the relative distances of planets are, how far from the sun other planets are compared with Earth. We had a scale of knowing that Mercury was closer to the sun, that VIII, that we had a scale of knowing that Mercury was closer to the sun, that Venus then was closer to the sun, then it was us, and then it was Mars. So we figure out our position in the solar system. That's Chilean astronomer Dr. Barbara Rojas Ayala.

She said Kepler outlined those ratios, but the actual distance from the sun to the earth alluded us. Luckily, there's a cosmic event that happens roughly every 120 years, a pair of sightings eight years apart, that would give us a glimpse of our true place in the source. solar system. It's called the Venus Transit. And a really important one began in 1761. This set off the space race of the 18th century. Or as Barbara would describe it, Odysseys, in the sense that they have to have pass all of these obstacles in order to get to a place

and settle there with their instruments and everything and hope for a sunny day with no class. to be able to measure this transit. The treasure they were searching for was exact measurements of Venus crossing in front of the sun. You could see it from various far-flung points in the world, which would make this a massive global undertaking. Countries spent fortunes to send astronomers around the world, all to measure a tiny black speck moving across the sun.

Not only that they didn't make it to the place where they wanted to be, they weren't able to do the observations and some of them died right after, you know, the transits happened. Take one trip led by the French explorer Jean-Baptiste Chapp dutrush. Barbara says he traveled to Siberia for the first transit and a lot of his instruments were destroyed. But he made his measurements and then headed to Mexico for the second transit of Venus.

They couldn't find a ship to cross the Atlantic Ocean. Then they finally found one. It's really small. They thought they were going to die there. It's a trip of three months, just seeing water, and that's it. And then they were hit by a hurricane. Then they had to walk across, you know, Mexico City, and then finally get to the place where they think that it's the best place to measure this

and realize that in that town there is a typhous epidemic, and people were dying. The crew makes the decision of stay and do the measurements. And the French explorer? He dies two months later. And only one person of the crew survived all of this and was able to go back to Paris and present the measurements that they have done. Today on the show, we revisit the 18th century space race

with the help of our friend Venus, a planet you can see every clear night as the sunsets. Plus, how triangles in space give us our address in the solar system. I'm Regina Barber, and your listening. Listening to Shortwave, the science podcast from NPR. Before we continue the drama that is the 18th century space race, there's a little bit more science and math you have to know. Because to understand how astronomers first measured the distances to stellar objects relatively close to Earth, you got to think in triangles. Which we're going to do right now.

So you need a few things. First, your two eyes. because the distance between your two eyes is the base of the triangle you're forming. If you know the distance between your pupils, that is usually like six centimeters. Second, your thumb, so that, per Barbara's instructions, you can extend your arm and see your thumb. And finally, find a faraway object like a mountain range or, you know, just a tree. That way. You can close one eye and you will see that your thumb is in front of, I don't know, something.

right, a tree. And then when you open the other eye and close the one that you had opened, you will see that that thumb basically changed position. Now it's covering something else. So let's tie this all together. You can use how much your thumb moves when you cover one eye in combination with the distance between your eyes. And you can figure it out with basic trigonometry the distance, or in this case, for example, how long is my arm by using a right triangle. and voila. That is what it's the parallax. It's this change of position

with respect to background objects of whatever you're looking. Okay, if you're like Regina, what the heck does Parallax have to do with the 18th century space race? Fear not, dear listener, I'm about to connect all the dots. I swear.

The last dot is astronomer Edmund Haley. In the late 1600s, he proposed we used Parallax, this I-Thither, thumb distant object trick to unlock the mystery of distances in outer space. Specifically, using our old friend from earlier. The transit of Venus. The transit of Venus.

All you got to do is make Venus your thumb. Substitute two points on Earth for your eyeballs. And finally, swap that background object for the sun. By moving to different places around the globe, they were able to measure that distance to Venus, and since we have this scale that Kepler gave us, we could measure the distance to the sun. This is huge, because when we get the exact distance to Venus using this parallax method, we instantly know the distances to all the other planets, and the whole solar system snaps into place. But remember, to unlock this boss level of a space measurement, you actually need two different locations on Earth.

Re-enter this 18th century space race. There are so many explorers rushing and dying to get the perfect measurements that it's actually difficult to pinpoint who the winner was. And many of these teams publish their results. But the legacy lives on today. Their results have been refined over centuries with new technology like radar. And our friend Parallax? We can also use it to measure the distance to relatively close stars.

What we can use as a baseline, it's basically the orbit of the Earth around the sea. Sun. Think of where Earth is in June compared to where it is in December, way on the other side of the sun. The larger your baseline, the better your measurement, and you're going to be able to measure things that are farther away. A nearby star will move ever so slightly in the sky in the span of that six months compared to the very, very far away background stars. And recently, scientists have been able to use Parallax to massively fill out our celestial map with the help of a space observatory. Now everything is changing just because there is a new mission that is called Gaia, that it's observing way much more stars. For this big triangle, telescopes on the ground form a base

with the Gaia spacecraft. And Gaia? It helps scientists reach a new level in celestial mapping. It's used to sleuth around our galaxy and it can even detect dim objects that are not quite planet, not quite star. They're known as brown dwarfs. There are way much more harder to see. And we wanted to know how many of them actually are. Barbara loves to uncover these dim objects because not only are they super cool. Among other things, they help us look into the past. The light doesn't arrive to us immediately.

So whatever I see now, it's something that already happened. Right? So I'm seeing the past. And in that sense, we are cosmetic. archaeologists. The Gaia mission is about as big a triangle as we can form. So when scientists want to appear beyond our local galactic neighborhood, they have to go beyond parallax. If you're interested in that great parallax beyond,

check out our episode notes. We put links to our entire series on how scientists mapped the cosmos using starlight. This episode was produced by Thomas Liu and edited by Rebecca Ramirez, Gabriel Spitzer, and Giselle Grayson. It was fact-checked by Rachel Carlson. The audio engineer for this episode was Josh Newell. Our higher-ups, our senior director Beth Donovan, and senior vice president Anya Grenman.

I'm Regina Barber. Thanks for listening to Shortwave, the science podcast from NPR.