Telescope

van den Vlekkert 1 1. What are the major functions of a telescope? The major functions of a telescope are to collect light from an astronomical source, resolve more detail, and magnify the image. 2. What two different components of a telescope can be used to focus light? The two components that help a telescope focus on light are the two lenses and a mirror. The latter gather the light and reflect it back to the focal point. Lens are used to gather more light than the human eye could collect on its own, producing a brighter, clearer, and magnified image. 3. Why bother making space-based telescopes? Ground-based telescopes, in compassion to space-based telescopes, have more to offer: they are bigger, built for less money, easier to maintain and upgrade. Most importantly, they have a lower risk of being damaged by debris in space. But space-based telescopes are able to do some things ground-based telescopes cannot: get a sharper image of what lies beyond the atmosphere. Space-based telescopes lie beyond the atmosphere and are able to observe wavelengths from the electromagnetic spectrum that are unable to reach Earth because of the atmosphere’s blurring effect. This allows researchers to gain a sharper image of what lies beyond the atmosphere and what is out of view from the naked eye. 4. What major problem did the Hubble telescope originally have, and how was it corrected? The Hubble Telescope, a space-based telescope that was launched into low Earth orbit in 1990, had a major issue in the main mirror. Hubble’s main mirror was defective- a spherical aberration caused by a manufacturing error. This error was approximately 1/50th the thickness of a sheet of paper, but it caused the telescope to send back incredibly blurry images that were almost unusable. In order to remedy this, NASA spent three years developing a solution. On December van den Vlekkert 2 2nd, 1993, a team of seven was sent to the Hubble and installed two Wide-Field Planetary Camera 2, or WFPC-2, effectively repairing the Hubble. 5. Briefly describe the three types of telescopes (shape? Lens? Mirror? Both? Cost? Use?) There are three types of telescopes: refractors, Newtonian reflectors, and catadioptric. Refracting telescopes are a type of telescope that uses one or more glass lenses to bend and focus the lights. Light passes through the lenses. In contrast to other telescopes, they lack a mirror. These are considered to be the favored telescope for amateurs and cost between half a thousand to over a thousand dollars. Newtonian telescopes are a type of telescope that uses a curved mirror to focus light onto a point. Light passes all the way down the tube onto a concave mirror where light is reflected back up the tube, focused on a secondary mirror. Finally, the second mirror reflects the light out of the tube at a right angle and into an eyepiece. From a price standpoint, it is the cheapest. The cost of these range between three hundred to over a thousand. Lastly, the catadioptric telescope is a telescope that uses both lenses and mirrors to focus on light. They are much more compact than a Newtonian or refracting telescope. In terms of cost, it ranged between three hundred to over a thousand, truly depending on the type of catadioptric telescope. 6. What is the difference between good ‘seeing’ and good ‘transparency’? Give one condition for each. Transparency is the clarity of the sky. Some conditions for good transparency would include after rain or after wind. On the other hand, seeing is the lack of turbulence in the sky. Smog is actually a great condition for good seeing. van den Vlekkert 3 7. Which of the seven types of EM spectra can survive the trip through our atmosphere and reach the ground (even if it is just partially)? With the exception of visible light, radio waves are the only other electromagnetic wavelengths that can survive through Earth’s atmosphere. This is because they have much longer wavelengths than any other wavelength. 8. Which telescope can produce brighter images (gather more light)? A. 5” B. 6” C. 8”: An 8-inch telescope produces brighter images than the others. This is because an 8-inch telescope can detect over 2000 times more stars than the naked eye. 9. Why is magnification NOT the most important consideration in purchasing a telescope? Contrary to what most people might assume, magnification is not the most important consideration in purchasing a telescope: aperture is. The larger the aperture of a telescope, the more light-gathering power it has and the finer detail it can resolve. 10. If two stars are separated by only 0.85” (seconds of arc) in the sky, which of the following telescopes would only see one star? One with a resolving power of: a. 0.50” b. 0.90” c. 0.85” If two stars were separated by only 0.85” in the sky, the one with the resolving power of .50” would only see one star. This is because it has a lesser resolving power than the others. 11. Define the following terms: • light gathering power: The ability of a telescope to collect a greater amount of light than the human eye. • resolving power: The ability of an optical instrument or type of film to separate or distinguish small or closely adjacent images. van den Vlekkert 4 • Magnification: The action or process of magnifying something or being magnified, especially visually. • exit pupil: The image of the aperture stop in the optics that follow it. • refractor: A lens or other object that causes refraction • reflector: A piece of glass, metal, or other material for reflecting light in a required direction. • Schmidt-Cassegrain: A catadioptric telescope that combines a Cassegrain reflector’s optic path with a Schmidt corrector plate to make a compact astronomical instrument that uses simple spherical surfaces. • transparency: A measurement of how clear the sky is. • seeing: The sharpness of a telescopic image.