ConceptChecks
ConceptCheck 6-1: The diameter, because it is the width of the opening that determines how much light can be captured by the telescope.
ConceptCheck 6-2: The thin lens bends light less, so, according to Figure 6-5, it must focus light at a more distant location. Thus, the thinner lens has the greater focal length.
ConceptCheck 6-3: The larger the eyepiece focal length, the smaller the magnification.
ConceptCheck 6-4: Reflection off a mirror does not depend on wavelength. This is a key advantage for a reflecting telescope, because it prevents the chromatic aberration that blurs images in telescopes made from lenses.
ConceptCheck 6-5: The angular resolution is decreased for larger telescope diameters. This improves the sharpness of the image, by reducing the angle that light is spread out and blurred by the telescope. Therefore, a larger telescope is better in two ways: sharper images of even dimmer features.
ConceptCheck 6-6: Adaptive optics actuators slightly deform the telescope’s mirror to match the apparent movement of a star due to distortions in Earth’s atmosphere. The actuators must deform the mirror even more on nights when the atmosphere is fluctuating more rapidly.
ConceptCheck 6-7: Photographic film only captures 2% of the light it receives. For a faint star, there might be very little light captured by the film. CCDs, on the other hand, are 35 times more sensitive, capturing 35 × 2% = 70% of the light they receive.
ConceptCheck 6-8: No. Instead of the CCD capturing a focused image of the planet, the spectrograph device spreads light from the planet out in wavelength to form a spectrum. A choice must be made to either look at an image using imaging equipment, or to look at a spectrum using a spectrograph.
ConceptCheck 6-9: If more than one radio dish is connected together, the distance between the two dishes—not the size of the dishes—determines the telescope’s overall diameter when considering the angular resolution. Thus, two dishes at 200 m produce sharper images than a single 100-m dish.
ConceptCheck 6-10: Given these three choices, astronomers would much prefer to have a new telescope in the microwave region because X-rays and ultraviolet wavelengths rarely pass through Earth’s atmosphere to the ground. While the atmosphere absorbs some portion of microwaves, not all microwaves are absorbed.
ConceptCheck 6-11: Orbiting space telescopes are placed far above most of Earth’s atmosphere. Without Earth’s atmosphere to absorb infrared, ultraviolet, X-ray, and gamma-ray light, astronomers can study the universe at these wavelengths.