Best of Blue Dot: Sky ghosts of the cosmos: Comets
Jun 19, 2026 · 52 min · 12 segments
Host Dave Schlom is joined by two scientists from the SETI Institute in Mt. View, California, to talk about one of hisfavorite celestial phenomena -- comets.
Jun 19, 2026 · 52 min · 12 segments
Host Dave Schlom is joined by two scientists from the SETI Institute in Mt. View, California, to talk about one of hisfavorite celestial phenomena -- comets.
Comets are probably, I, I would say for me, the most fascinating object that I've ever observed as a, as an amateur astronomer.
You know, back in ancient times, Ariel, uh, Aristotle thought that comets were part of the atmosphere.
Talk a bit about, uh, you know, what you know about the evolution of our understanding of comets from ancient times to the, you know, when we first started to figure out, oh, these are objects that are orbiting the Sun.
Like you said, at first, uh, Aristotle thought that comets were- W- within our own atmosphere.
Um, a lot of people mix up comets and meteors, and when you imagine a, a meteor shower, um, those little streaks, uh, that go through our atmosphere, they kind of look like comets for a s- very short instant, you know? Um, so I could kind of understand where that thought comes from.
Um, but then, uh, through, uh, much later, thousands of years later, um, Tycho Brahe measured a comet's parallax.
Uh, and a parallax tells you how far away something is, and he found out that, oh, these comets are much farther away than within our atmosphere.
Um, but at that point they knew, okay, these things aren't interacting with our atmosphere.
Um, but it still wasn't until later, um, with Edmund Halley actually, who figured out that these objects must be orbiting the sun, uh, because he noticed that this comet that he observed, which ended up later being named after him, Comet Halley, uh, has been... has appeared many times in history, in pictures back in 1456, 1531, 1607, 1682.
There's been this comet that seems to follow this period that he was able to predict.
Uh, and so he said, "Okay, it's gonna come back around, um, I know it, in 76 years." Um, and that is if this comet is orbiting the sun.
Um, so he worked there to confirm Newton's laws of gravity really, uh, to show that comets are actually going around the sun just like the planets are.
It was the first thing other than the planets that, uh, astronomers discovered to be going around the sun.
Comets are probably, I, I would say for me, the most fascinating object that I've ever observed as a, as an amateur astronomer.
You know, back in ancient times, Ariel, uh, Aristotle thought that comets were part of the atmosphere.
Talk a bit about, uh, you know, what you know about the evolution of our understanding of comets from ancient times to the, you know, when we first started to figure out, oh, these are objects that are orbiting the Sun.
Like you said, at first, uh, Aristotle thought that comets were- W- within our own atmosphere.
Um, a lot of people mix up comets and meteors, and when you imagine a, a meteor shower, um, those little streaks, uh, that go through our atmosphere, they kind of look like comets for a s- very short instant, you know? Um, so I could kind of understand where that thought comes from.
Um, but then, uh, through, uh, much later, thousands of years later, um, Tycho Brahe measured a comet's parallax.
Uh, and a parallax tells you how far away something is, and he found out that, oh, these comets are much farther away than within our atmosphere.
Um, but at that point they knew, okay, these things aren't interacting with our atmosphere.
Um, but it still wasn't until later, um, with Edmund Halley actually, who figured out that these objects must be orbiting the sun, uh, because he noticed that this comet that he observed, which ended up later being named after him, Comet Halley, uh, has been... has appeared many times in history, in pictures back in 1456, 1531, 1607, 1682.
There's been this comet that seems to follow this period that he was able to predict.
Uh, and so he said, "Okay, it's gonna come back around, um, I know it, in 76 years." Um, and that is if this comet is orbiting the sun.
Um, so he worked there to confirm Newton's laws of gravity really, uh, to show that comets are actually going around the sun just like the planets are.
It was the first thing other than the planets that, uh, astronomers discovered to be going around the sun.
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