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Reflection
The incident light traveling at an angle (i) reflects off a surface at the same angle (r) between the reflected ray and the perpendicular (p).
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Refraction
The change in the direction of light as it passes through a medium. Light slows as it passes through a denser medium than a vacuum.
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Lens
Glass that is shaped to make distant objects closer and brighter.
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Mirror
Glass that is coated with silver, aluminum, or a similar highly reflective substance that reflects light waves.
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Spectroscopy
Measures the spectra of an object, not recording an image of an object. A diffraction grating is used to break up light into a spectrum.
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Hubble Space Telescope
A telescope that orbits the earth at 600km. It can measure any wavelength of light from 115 nm to 1 micro n.
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Atmospheric Distortion
The bending of light by the earth’s atmosphere.
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Prime Focus
An observer or instrument is placed directly at the focal point, within the barrel of a telescope. Used only in large reflecting telescopes.
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Cassegrain Focus
Has a convenient, accessible focal point in a telescope. A hole is drilled directly through the center of the primary mirror, and a convex secondary mirror placed in front of the original focal point reflects the light rays back through the hole.
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Angular Resolution
A quantity that gauges how well fine details of objects can be seen. It is the angle between 2 stars. The smaller the angle, the sharper the resolution.
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Adaptive Optics
A system that compensates for atmospheric turbulence, so that the angular resolution can be smaller than the size of the seeing disk. As turbulence causes a star to “dance” around, sensors detect the “dancing” and adjust the mirror accordingly.
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Secondary Mirror
A convex mirror that is placed in front of the original focal point in a reflecting telescope. It reflects light rays from the primary mirror to an observer, instrument, or another mirror.
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Interferometry
A technique designed to improve angular resolution. The idea is to have 2 widely separated telescopes observe the same object at the same time, then use fiber optic cables to pipe the light signals to a central location, where they are combined to form a single image.
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Photometry
The measurement of the brightness of stars and other astronomical objects.
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Newtonian Reflector
A reflecting telescope that has a flat mirror at a 45 degree angle in front of the focal point in the barrel of a telescope. This secondary mirror reflects the light rays to one side of the barrel, where an eyepiece lens is placed to magnify the image.
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Light Gathering Power
The light-gathering power of a telescope is directly proportional to the objective lens, which is proportional the square of the lens diameter.
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Primary Mirror
A concave mirror that that reflects light rays to a focal point.
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