8/12/2023 0 Comments Doppler shift astronomyYou throw them one per second, but because you’re moving toward the target, each tennis ball has a little bit less distance that it has to travel. So you can imagine that you have a bucket of tennis balls and for some crazy reason you’re running toward a target, throwing tennis balls at the target and every tennis ball you throw, you throw at the exact same velocity. Pamela: And the rate at which these waves hit your ear can be affected by how you’re moving, or how the object emitting the sound is moving. If they’re hitting really quickly, then we hear a high-pitched noise, and if they’re very slowly or not as often, then we hear a lower-pitched noise. Whereas if the compression waves are coming with more time between them, we hear that as a lower-pitched noise.įraser: Right, ok… so the pitch of the sound that we hear is purely how often these compression waves are bonking into our eardrum. ![]() Pamela: So, that constant noise is actually made up of a whole series of compression waves through the air where the air molecules get a little bit packed together, and each of these packed-together lumps of air, as they hit your eardrum, they cause it to vibrate and the faster your ear’s getting hit by the vibrations, the higher pitched you hear the noise. So when you’re listening to a constant-pitch noise… when you’re listening to the constant noise of a trumpet player playing a single note…įraser: Right, or like a car engine… like a really loud car engine… Actually, if anyone’s every seen a car race… like a Formula One going past you… oh, you really hear it. Pamela: Well, the best way to think of it is that you’re changing the rate at which things arrive simply by shortening the distance they have to travel. Ok, Pamela, so let’s use that concept of you standing there and some object is speeding towards you to explain the Doppler effect. Astronomers use the Doppler effect to study the motion of objects across the universe, from nearby extrasolar planets, to the expansion of distant galaxies. It works for sound waves and it works for light waves. We’re having a very unusual cold snap, so, normally I work upstairs in the winter where it’s nice and warm at the kitchen table… you can see the sun… but, I’m downstairs in my recording studio and got about eight layers of clothing on… gloves… and I wanna get out of here… So let’s get this show over with really quick!įraser: So you know how a police siren changes sound when it passes by you… that’s the Doppler effect. 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 165 for Monday November 23, 2009, Doppler Effect.
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