Telescope Aperture Quiz: Do You Know What Matters?

1. Which part of a telescope or camera determines its light-gathering power?

The length of the tube

The eyepiece

The aperture

The tripod

The color of the lens

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.

Explanation

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.

2. If you double the diameter of a telescope's aperture, how much does the light-gathering area increase?

2 times

4 times

8 times

16 times

50 percent

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.

Explanation

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.

3. A telescope with a 10-inch aperture gathers more light than a telescope with a 5-inch aperture.

True

False

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.

Explanation

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.

4. Why is light-gathering power more important than magnification for viewing faint stars?

Magnification makes stars look bigger

Light-gathering power makes faint objects appear brighter

Magnification changes the color of the star

Faint stars do not need magnification

Magnification is only for the moon

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.

Explanation

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.

5. In a reflecting telescope, what acts as the aperture?

The small flat mirror

The secondary lens

The primary parabolic mirror

The glass window at the front

The camera sensor

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.

Explanation

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.

6. The total surface area of the primary lens or mirror that collects light is called the collecting ____.

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.

Explanation

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.

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7. Which of these is a common unit used to measure the aperture of a hobbyist telescope?

Watts

Millimeters

Volts

Newtons

Kilograms

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.

Explanation

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.

8. How does a larger aperture affect the resolution (sharpness) of an image?

It makes the image blurrier

It has no effect on sharpness

It allows for finer details to be seen

It turns the image upside down

It makes the image smaller

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.

Explanation

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.

9. The light-gathering power of a telescope is proportional to the diameter of the aperture.

True

False

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.

Explanation

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.

10. If a telescope has an aperture of 100mm and another has 300mm, how many times more light does the 300mm telescope gather?

3 times

6 times

9 times

12 times

30 times

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.

Explanation

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.

11. What is the main reason professional observatories build larger and larger telescopes?

To make them taller

To gather more light from distant, faint objects

To see colors that don't exist

To block out the wind

To make the telescopes heavier

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.

Explanation

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.

12. A device that uses a lens as its primary aperture is called a ____ telescope.

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.

Explanation

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.

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13. What happens to the image of a star if you use a telescope with a very small aperture?

The star looks like a giant disk

The star appears very dim or invisible

The star changes from blue to red

The star starts to blink

The star looks closer

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.

Explanation

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.

14. Increasing the aperture of a telescope also increases its ability to see through clouds.

True

False

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.

Explanation

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.

15. Which mathematical shape is used to calculate the light-gathering area of a standard lens?

Square

Triangle

Circle

Hexagon

Sphere

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.

Explanation

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.

16. What is the aperture of a human eye in the dark (approximately)?

1mm

7mm

25mm

50mm

100mm

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.

Explanation

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.

17. The ratio of the focal length to the aperture diameter is known as the ____.

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.

Explanation

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.

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18. Why does a larger aperture allow for higher useful magnification?

Because it makes the telescope heavier

Because it provides enough light to keep the image bright at high power

Because it changes the gravity of the lens

Because it filters out the sun

Because it makes the eyepiece wider

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.

Explanation

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.

19. For a telescope, aperture is usually measured in inches or millimeters.

True

False

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.

Explanation

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.

20. If you have two telescopes of the same length, but telescope A has a wider tube and lens than telescope B, which one is "faster" (gathers more light per second)?

Telescope A

Telescope B

They are the same

Telescope B because it is thinner

Neither gathers light

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.

Explanation

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.

Size vs. Sight: The Telescope Aperture Quiz

1. Which part of a telescope or camera determines its light-gathering power?

2. If you double the diameter of a telescope's aperture, how much does the light-gathering area increase?

3. A telescope with a 10-inch aperture gathers more light than a telescope with a 5-inch aperture.

4. Why is light-gathering power more important than magnification for viewing faint stars?

5. In a reflecting telescope, what acts as the aperture?

6. The total surface area of the primary lens or mirror that collects light is called the collecting ____.

7. Which of these is a common unit used to measure the aperture of a hobbyist telescope?

8. How does a larger aperture affect the resolution (sharpness) of an image?

9. The light-gathering power of a telescope is proportional to the diameter of the aperture.

10. If a telescope has an aperture of 100mm and another has 300mm, how many times more light does the 300mm telescope gather?

11. What is the main reason professional observatories build larger and larger telescopes?

12. A device that uses a lens as its primary aperture is called a ____ telescope.

13. What happens to the image of a star if you use a telescope with a very small aperture?

14. Increasing the aperture of a telescope also increases its ability to see through clouds.

15. Which mathematical shape is used to calculate the light-gathering area of a standard lens?

16. What is the aperture of a human eye in the dark (approximately)?

17. The ratio of the focal length to the aperture diameter is known as the ____.

18. Why does a larger aperture allow for higher useful magnification?

19. For a telescope, aperture is usually measured in inches or millimeters.

20. If you have two telescopes of the same length, but telescope A has a wider tube and lens than telescope B, which one is "faster" (gathers more light per second)?