The interaction of light and glass is extraordinarily complex, as you can see in the video above.
Field Of View
One of the downsides of ever more powerful telescopes is that with higher magnification generally comes a smaller field of view.
Raising a Glass
Glass has the useful feature of being transparent at optical wavelengths. That, and the fact that light can refract (change direction) when it passes through curved glass is what made it useful as lenses, and eventually telescopes.
Star of Bethlehem
When stars are portrayed in media, they are often shown with long spikes emanating from them. Perhaps the most common example is that of the “star of Bethlehem” which, according to the story, led the wise men to baby Jesus. Of course when we look at stars in the night sky, we don’t see any such spikes. Stars twinkle due to atmospheric disturbances, but that’s about it. In photographs, however, bright stars often have such long spikes. So what causes them? It all has to do with an interesting bit of optics.
Adaptation
If you’ve ever looked up in the night sky you’ve seen the twinkling of the stars. This twinkle is not due to the stars themselves, but to the turbulent motion of the Earth’s atmosphere. As starlight enters our atmosphere, the variations in density in turbulent air cause the light wave fronts to distort. So instead of reaching the telescope evenly like even rows of a band on parade, the wave fronts come in uneven and wobbly. This wobbly behavior is why stars appear to twinkle.
Losing Direction
Launched in 2009, Kepler was intended as a “planet hunter” telescope. It finds planets by observing stars for long periods of time. To make long observations, Kepler needs to be able to point in the same direction very precisely, and it must be able to adjust its direction if it starts to drift. So how do you keep a telescope oriented?
Reading the Rainbow
Our eyes see color through cones in our retina, where the three different types (S, M, and L) each have a slightly different range of wavelengths to which they are light sensitive. Through the response of these different cones our brains are able to distinguish different wavelengths of light, which we interpret as color. Telescope detectors typically have a much wider range of light sensitivity, which is good if you want to detect a great deal of light, but not so good if you want to observe a particular color range. So many telescopes have filters that block light outside a particular range.
Aberration
A simple telescope can be made from basic lenses or mirrors, but a good telescope must be designed to account for optical aberrations.
Scale
When something is far way, it can look quite small. That is why the resolving power of your instrument is so important.
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