![]() So you can imagine it like a bicycle wheel that the moon is attached to the outside of the bicycle wheel and the bicycle wheel is rolling itself around the moon’s perfectly circular orbit. Pamela: …tiny circle on top of the perfect circle. Pamela: And noticing all this, he sat down and tried to run the math assuming epicycles to try to figure out what’s going on based on the changes in size that he was able to observe.įraser: So, epicycles… this is where the moon is orbiting the earth in a perfect circle but then it’s on a little…. It actually changes in brightness, there are some full moons that are a lot brighter than others. When he watched it through what’s called the diopter, he was able to tell that sometimes it was a little bit bigger, sometimes it was a little bit smaller, and this was an interesting discovery back in the days when we thought all orbits were perfect circles.įraser: Right, right, I mean the moon changes like 15% from its most distant point to its closest point. So he noticed things like… the moon has an obvious change in size over time. He was one of the early scientists who based his discoveries not on philosophy, not on shadows on cave walls, but on looking. ![]() It was in putting all these pieces together that Hipparchus was able to make some really amazing discoveries. And as he traveled and as he measured, he worked with others to try to figure out… if I’m seeing this, what are you seeing when you are. He was working in the Mediterranean… he was at Rhodes for some of his measurements, he was in Egypt for others. Pamela: He was a mathematician, he was a geometrist. But in terms of things we can get our hands on and study easily, well we can’t necessarily get our hands on the work by Hipparchus… not in all cases… but his work, his original star maps from basically 150 B.C., his original work throughout his life, it was used as the base information for the Almagest by Ptolemy, which is perhaps one of the most famous early astronomy books. Pamela: Yeah, so those names all came down from the ancient Babylonians. That’s where we start getting squirrelly names like Zubenelgenubi for different stars and Betelgeuse which leads to many arguments over *betelgice,* *beetlejuice,* whatever…įraser: Right, but we have to thank the Babylonians for that name… wow… Star maps though, those started being made originally by the ancient Babylonians. Pamela: Well, it’s impossible to know exactly when people realized that… well, wow, you see the Plow every night, you see whatever your favorite constellation is year after year after year… always appearing in the same season. And I think the name that comes to mind is Hipparchus, so how did this all come about? Alright Pamela, well I guess we need to go right back to the earliest age, and I guess at some point, humans realized that there was some kind of rhyme or reason to the position of the stars… that they weren’t going anywhere, that there’s a way to map this. This is astrometry… another way to find our place in the universe. So, astronomers have been cataloging star positions for thousands of years from the first calculations made by Hipparchus to the more recent star catalogs made by the spacecraft named after him. But yeah, if you want to email us and want us to do a little promo for you, no problem. Use our content for any purpose whatsoever. For free… go ahead… play it all you like. Free… don’t pay ever! Yes, that would be fine with us… would be great if you want to do that… college radio, NPR, or here in Canada on the CBC… CBC–call me! And ABC in Australia… anything. One little piece of news… which is that we’ve had a couple of radio stations ask if they can run Astronomy Cast on the air and want our permission, and… YES! So if you run a radio station, if you know a radio station and you want to use Astronomy Cast, feel free… be our guest. Pamela Gay, a professor at Southern Illinois University Edwardsville. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. Fraser: Astronomy Cast Episode 182 for Monday March 22, 2010, Astrometry.
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