Size vs. Sight: The Telescope Aperture Quiz

If an object is very far away, then very few of its photons reach Earth. If we want to see these objects, we need a massive aperture to catch as many of those rare photons as possible.

If Telescope A has a wider lens, then its aperture is larger. If the aperture is larger, it collects more photons in the same amount of time, making it "faster" for photography and brighter for viewing.

If aperture is the physical width of the optics, it must be expressed in linear measurements. Inches (imperial) and millimeters (metric) are the two standard units used by manufacturers and astronomers.

If we increase magnification, we are spreading the collected light over a larger area of our retina. If we don't have a large aperture to provide a lot of light to begin with, the image will become too dim to see as we zoom in.

If we take the length of the light path and divide it by the width of the opening, we get a specific optical ratio. This is commonly referred to as the f-number or focal ratio.

If the human pupil dilates to let in more light in the dark, it reaches a maximum width. In most humans, this maximum diameter is roughly 7 millimeters.

If most lenses and mirrors are manufactured as circular disks, then the area facing the sky is a circle. Therefore, we use the area of a circle formula to determine light-gathering power.

If clouds are present, they physically block or scatter visible light. While a larger aperture gathers more light, it cannot "see through" solid water droplets or ice crystals in the atmosphere that the light cannot pass through.

If the aperture is small, then only a tiny amount of light is collected. If there isn't enough light to trigger the sensors in our eyes or a camera, then the star will appear extremely faint or not be seen at all.

If a telescope uses a glass lens to bend and focus light, then it is performing refraction. Therefore, it is classified as a refracting telescope.

If we want to collect more light, then we must increase the size of the opening. The aperture is the diameter of the primary lens or mirror that allows light to enter. Therefore, the aperture is the primary factor in light-gathering power.

If we compare the diameters, the 300mm telescope is 3 times wider than the 100mm telescope. Since light-gathering power follows the square of the ratio (3 squared), then 3 times 3 equals 9.

If light-gathering power is based on the area (radius squared), then it is proportional to the square of the diameter, not just the diameter itself. Therefore, saying it is proportional to the diameter is mathematically incorrect.

If a larger aperture is used, then it reduces the effects of diffraction (the bending of light). If diffraction is reduced, then the telescope can distinguish between two points that are very close together, resulting in a sharper image.

If aperture is a measurement of the width or diameter of a lens, then it must be measured in units of length. Among the choices, millimeters is the only standard unit of length used for optical diameters.

If we are measuring how much space is available to catch falling light, then we are calculating the area. Therefore, the term used is the collecting area.

If a reflecting telescope uses a mirror to bounce light to a focus, then the size of that first large mirror determines how much light enters the system. Therefore, the primary mirror's diameter is the aperture.

If a star is too faint to see, then making it look "bigger" through magnification just spreads the tiny amount of light out even more. If we increase light-gathering power, we collect more total photons, which makes the object bright enough for the eye to detect.

If light-gathering power depends on the surface area of the lens, then a larger diameter results in a larger area. Since 10 inches is greater than 5 inches, the 10-inch telescope has a larger surface to catch photons.

If the aperture is circular, then its area is calculated using the formula for the area of a circle (pi times radius squared). If the diameter doubles, then the radius also doubles. Since the radius is squared in the area formula, two squared equals four, meaning the area increases by a factor of four.