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Which of the following two telescopes has a better angular resolution? 1) the Hubble Space Telescope (2.4 meter aperture) at optical wavelengths and 2) the Very Long Baseline Array (VLBA), a radio interferometer with a maximum baseline of 8600 km observing at 1 mm wavelengths. (Please answer with either HST or VLBA)
The Event Horizon Telescope is attempting to image the supermassive black hole at the center of the Milky Way using Very Long Baseline Interferometry. Using the angular resolution you found above, how big of an object at the center of the Milky Way can the Event Horizon Telescope resolve? (Please express your answer in units of solar radii.)
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Refraction at plane surfaces
Refraction and light bending
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You might have heard people talk about Einstein’s speed of light, and that it’s always the same. The part that most people leave out is that this is only true in a vacuum—when there’s no pesky molecules of air or water to slow it down. But when light moves through a more familiar medium like air, it moves more slowly due to the interactions of individual photons with the molecules in the material. In general, the more optically dense the medium, the slower the light will move. So what happens to the light when it goes from one medium to another?
Light changes speed
Imagine that you and your friends are at the beach. You all decide to swim together, so you link arms and approach the water as a straight line. As you start walking into the water, you all slow down, because it’s harder to walk through water than through air. So imagine that you approach the water at an angle relative to the shoreline. The person on the end will meet the water and slow down first, then the next person in line, then the next, until everyone is walking through the water. Because one end of the line slowed down before the other end, the line of people becomes crooked, with the people who are still on the beach at a different angle relative to the water’s edge than the people who have already entered the ocean.