by Nereid » Fri Mar 02, 2012 1:49 pm
Another thing to keep in mind is that gravitational lensing is achromatic; the observed effect is exactly the same, whether you're observing it in the red part of the visual waveband or the blue ... or in UV, or IR, or x-rays, or radio! So, for example, the apparent position of a quasar - one that's 'radio loud' - is shifted exactly the same amount by the Sun's gravitational field when you observe it with an optical telescope or a radio telescope.
The more traditional lensing - think of light, with a magnifying glass - is chromatic; the amount a physical lens (whether it's made of glass, or air, or the rarified plasma of the solar wind, etc) deflects electromagnetic radiation depends very much on the wavelength of that 'light'. A good example of this is scintillation: the atmosphere makes stars twinkle, and you can sometimes see quite colourful twinkles in bright stars very low down in the sky (a dark, clear sky is best). If you observe the same stars (quasars are better) in the radio part of the spectrum, they don't scintillate like this. However, you can observe scintillation of distant radio sources ... caused by the interplanetary (and interstellar) medium; observing these sources with a space-based (optical) telescope (like the Hubble) you don't see this scintillation.
Another thing to keep in mind is that gravitational lensing is achromatic; the observed effect is exactly the same, whether you're observing it in the red part of the visual waveband or the blue ... or in UV, or IR, or x-rays, or radio! So, for example, the apparent position of a quasar - one that's 'radio loud' - is shifted exactly the same amount by the Sun's gravitational field when you observe it with an optical telescope or a radio telescope.
The more traditional lensing - think of light, with a magnifying glass - is chromatic; the amount a physical lens (whether it's made of glass, or air, or the rarified plasma of the solar wind, etc) deflects electromagnetic radiation depends very much on the wavelength of that 'light'. A good example of this is scintillation: the atmosphere makes stars twinkle, and you can sometimes see quite colourful twinkles in bright stars very low down in the sky (a dark, clear sky is best). If you observe the same stars (quasars are better) in the radio part of the spectrum, they don't scintillate like this. However, you can observe scintillation of distant radio sources ... caused by the interplanetary (and interstellar) medium; observing these sources with a space-based (optical) telescope (like the Hubble) you don't see this scintillation.