Editing 2926: Doppler Effect
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Redshift is the same concept applied to wavelengths of light. Red has a longer wavelength than blue, so light-emitting objects get redder when they move away from us and bluer when they move toward us. We usually talk about redshift and not blueshift because while stars in our galaxy can move in any direction relative to us, most other galaxies are moving away from us. The fact that more distant galaxies are moving away quicker the farther away they are shows that the universe is expanding. | Redshift is the same concept applied to wavelengths of light. Red has a longer wavelength than blue, so light-emitting objects get redder when they move away from us and bluer when they move toward us. We usually talk about redshift and not blueshift because while stars in our galaxy can move in any direction relative to us, most other galaxies are moving away from us. The fact that more distant galaxies are moving away quicker the farther away they are shows that the universe is expanding. | ||
| β | Unlike the usual explanation of redshift as equivalent to the Doppler effect for sirens, a major component of the redshift of light from distant galaxies is due to the expansion of space in between us and the light source. This effect is not an important component of the Doppler shift for sirens | + | Unlike the usual explanation of redshift as equivalent to the Doppler effect for sirens, a major component of the redshift of light from distant galaxies is due to the expansion of space in between us and the light source. This effect is not an important component of the Doppler shift for sirens{{cn}}. Redshift has been mentioned multiple times before, including in [[2764: Cosmological Nostalgia Content]] and [[2853: Redshift]]. |
The title text claims that the Doppler effect particularly affects sirens. This isn't actually true, but it may seem like it because people hear Doppler shifts for sirens more than for other sounds. Sirens tend to employ predictable tone(s), which people who aren't {{w|Amusia|totally tone deaf}} would have experienced as a shift in pitch from a passing vehicle's siren, whereas something equally subject to Doppler shift like engine noise could also change pitch according to differences of speed and gearing. Then the text claims that the emoji for sirens is red because they're associated with redshift. Actually, the emoji is a picture of the rotating light on top of emergency vehicles; these tend to be used in conjunction with sirens, and they're red because this color typically signifies danger or warning (though, in fact, blue lights used with sirens are also common). | The title text claims that the Doppler effect particularly affects sirens. This isn't actually true, but it may seem like it because people hear Doppler shifts for sirens more than for other sounds. Sirens tend to employ predictable tone(s), which people who aren't {{w|Amusia|totally tone deaf}} would have experienced as a shift in pitch from a passing vehicle's siren, whereas something equally subject to Doppler shift like engine noise could also change pitch according to differences of speed and gearing. Then the text claims that the emoji for sirens is red because they're associated with redshift. Actually, the emoji is a picture of the rotating light on top of emergency vehicles; these tend to be used in conjunction with sirens, and they're red because this color typically signifies danger or warning (though, in fact, blue lights used with sirens are also common). | ||
