Telescope Array Synthesis: The Power of ALMA

1. What are the main benefits of using virtual large telescopes?

They can see the same detail as a telescope miles wide

They are cheaper than building a solid 10-mile-wide mirror

They can be upgraded by adding more small telescopes later

They can see through the center of the Earth

They provide better resolution than a single small telescope

If building a 10-mile wide solid mirror is impossible, then an array is the only way to reach that resolution; if the units are smaller, they are more affordable and the system is modular, meaning it can grow over time.

Explanation

If building a 10-mile wide solid mirror is impossible, then an array is the only way to reach that resolution; if the units are smaller, they are more affordable and the system is modular, meaning it can grow over time.

Submit

2. Which of these factors would improve the "Synthesized Beam" (the quality of the image) in telescope array synthesis?

Adding more telescopes to the array

Spacing the telescopes in a non-repeating pattern

Observing for a longer period of time as the Earth rotates

Using a shorter wavelength of light (like UV instead of Radio)

Painting the telescopes a bright color

If we have more telescopes and better spacing, we sample more of the "virtual mirror"; if we observe longer, Earth's rotation fills in the gaps; and if the wavelength is shorter, the resolution formula (lambda/D) results in a smaller, sharper beam. Undone.

Explanation

If we have more telescopes and better spacing, we sample more of the "virtual mirror"; if we observe longer, Earth's rotation fills in the gaps; and if the wavelength is shorter, the resolution formula (lambda/D) results in a smaller, sharper beam. Undone.

Submit

3. Why can't we just use one small telescope and magnify the image 1000 times instead of combining telescopes?

Magnification makes the stars disappear

Magnification only makes a blurry image larger without adding new detail

Small telescopes are too heavy

The star would get too hot

There is no reason; magnification works perfectly

If a telescope has a small aperture, its resolution is limited by diffraction; if the resolution is low, then "zooming in" just makes a blurry dot look like a bigger blurry dot without revealing any new features.

Explanation

If a telescope has a small aperture, its resolution is limited by diffraction; if the resolution is low, then "zooming in" just makes a blurry dot look like a bigger blurry dot without revealing any new features.

4. The use of virtual large telescopes that are located on different continents is called Very Long ________ Interferometry (VLBI).

If the "baseline" is the distance between telescopes, and if those telescopes are separated by thousands of miles (a very long distance), then the technique is named Very Long Baseline Interferometry.

Explanation

If the "baseline" is the distance between telescopes, and if those telescopes are separated by thousands of miles (a very long distance), then the technique is named Very Long Baseline Interferometry.

Submit

5. Interferometry concepts state that if two telescopes are 100 meters apart, the system acts like a 100-meter-wide lens for resolution purposes.

True

False

If resolution depends on the distance between the two most distant points of the "eye" or "aperture," and if those points are 100 meters apart in an array, then the system matches the detail-seeing ability of a 100-meter telescope.

Explanation

If resolution depends on the distance between the two most distant points of the "eye" or "aperture," and if those points are 100 meters apart in an array, then the system matches the detail-seeing ability of a 100-meter telescope.

6. How does the "correlator" help in combining telescopes?

It cleans the mirrors

It physically moves the telescopes closer

It mathematically compares and multiplies the signals from all pairs of telescopes

It provides electricity to the array

It acts as a shield against the Sun

If each telescope records a slightly different version of the same signal, then the computer must find the common patterns between them; if it multiplies these signals together to find the interference, then that process is called correlation.

Explanation

If each telescope records a slightly different version of the same signal, then the computer must find the common patterns between them; if it multiplies these signals together to find the interference, then that process is called correlation.

7. Which of the following are challenges of aperture synthesis explained in high school physics?

Atmospheric turbulence can distort the wave timing

The Earth's rotation changes the baseline constantly

Computers must process massive amounts of data per second

The telescopes might run out of oxygen

The signal from space is often very weak

If the air moves, it changes the path length of the light; if the Earth spins, the geometry of the array shifts; and if the array is large, the data rate is enormous. Telescopes in a vacuum or on Earth do not "breathe" oxygen.

Explanation

If the air moves, it changes the path length of the light; if the Earth spins, the geometry of the array shifts; and if the array is large, the data rate is enormous. Telescopes in a vacuum or on Earth do not "breathe" oxygen.

Submit

8. In the context of interferometry concepts, what is "constructive interference"?

When waves are destroyed

When the peak of one wave meets the peak of another to create a stronger signal

When telescopes are turned off

When the stars stop glowing

When the computer crashes

If two light waves are perfectly aligned so their crests overlap, then the total energy adds up; if the energy adds up to a higher intensity, then the result is known as constructive interference.

Explanation

If two light waves are perfectly aligned so their crests overlap, then the total energy adds up; if the energy adds up to a higher intensity, then the result is known as constructive interference.

9. The "Event Horizon Telescope," which took the first photo of a black hole, is a global telescope array ________.

If the project linked telescopes in Hawaii, Chile, and the South Pole to act as one Earth-sized camera, then it utilized the principle of array synthesis to achieve the required resolution.

Explanation

If the project linked telescopes in Hawaii, Chile, and the South Pole to act as one Earth-sized camera, then it utilized the principle of array synthesis to achieve the required resolution.

Submit

10. To succeed in telescope array synthesis, the signals from each telescope must be synchronized to a fraction of a wave cycle.

True

False

If the waves from different telescopes are not aligned (out of phase), they will cancel each other out randomly; if we want to extract information, we must know the exact arrival time of each wave peak to align them in the computer.

Explanation

If the waves from different telescopes are not aligned (out of phase), they will cancel each other out randomly; if we want to extract information, we must know the exact arrival time of each wave peak to align them in the computer.

11. What is the primary purpose of combining telescopes into an array?

To make the telescopes heavier

To increase the total magnification to 1,000,000x

To increase the angular resolution (detail) of the image

To change the color of the stars being observed

To prevent the telescopes from falling over

If the resolution of a telescope is determined by its diameter, and if building a single mirror kilometers wide is physically impossible, then linking multiple smaller telescopes allows them to act as one giant instrument to see finer details.

Explanation

If the resolution of a telescope is determined by its diameter, and if building a single mirror kilometers wide is physically impossible, then linking multiple smaller telescopes allows them to act as one giant instrument to see finer details.

12. Which of the following is a famous example of combining telescopes to study the universe?

The Hubble Space Telescope

The Very Large Array (VLA) in New Mexico

A pair of handheld binoculars

The magnifying glass

The North Star

If the VLA consists of 27 independent radio antennas that move along railroad tracks to change their distance, then it is a primary example of a functional telescope array using synthesis.

Explanation

If the VLA consists of 27 independent radio antennas that move along railroad tracks to change their distance, then it is a primary example of a functional telescope array using synthesis.

13. What happens to the "resolving power" of a system when the telescopes are moved further apart?

It decreases

It stays the same

It increases

It turns into heat

The telescopes stop working

If resolving power is the ability to see small details, and if that ability is inversely proportional to the diameter or baseline (theta = lambda / D), then a larger distance (D) results in a smaller detectable angle (theta), which means better resolution.

Explanation

If resolving power is the ability to see small details, and if that ability is inversely proportional to the diameter or baseline (theta = lambda / D), then a larger distance (D) results in a smaller detectable angle (theta), which means better resolution.

14. In interferometry concepts, the physical distance between the two furthest telescopes in an array is known as the ________.

If the resolution of an interferometer is calculated by dividing the wavelength by the distance between the elements, then that specific distance is defined in astronomy as the baseline.

Explanation

If the resolution of an interferometer is calculated by dividing the wavelength by the distance between the elements, then that specific distance is defined in astronomy as the baseline.

Submit

15. Virtual large telescopes created through an array collect as much total light as a solid mirror of the same diameter.

True

False

If light-gathering power depends on the total physical surface area of the mirrors, and if an array has large gaps between the small telescopes, then the array only collects as much light as the small mirrors added together, not the entire area of the gap.

Explanation

If light-gathering power depends on the total physical surface area of the mirrors, and if an array has large gaps between the small telescopes, then the array only collects as much light as the small mirrors added together, not the entire area of the gap.

16. Why is aperture synthesis explained more often in radio astronomy than in optical (visible light) astronomy?

Radio waves are faster than light

Radio wavelengths are much longer, making the timing easier to manage

Optical telescopes do not use mirrors

Radio telescopes are only built in the desert

Radio waves are heavier than visible light

If visible light waves are very tiny (nanometers), then the timing to align them must be impossibly perfect; if radio waves are centimeters or meters long, then electronic equipment can more easily sync the signals from different telescopes.

Explanation

If visible light waves are very tiny (nanometers), then the timing to align them must be impossibly perfect; if radio waves are centimeters or meters long, then electronic equipment can more easily sync the signals from different telescopes.

17. Which of the following are necessary components for telescope array synthesis?

Precise atomic clocks for timing

High-speed fiber optic cables or data links

A central computer called a "correlator"

A giant glass lens covering the entire array

Multiple individual telescope units

If signals must be combined with nanosecond precision, then atomic clocks and fast cables are required; if the signals must be mathematically merged, then a correlator is needed; if it is an array, then multiple units must exist.

Explanation

If signals must be combined with nanosecond precision, then atomic clocks and fast cables are required; if the signals must be mathematically merged, then a correlator is needed; if it is an array, then multiple units must exist.

Submit

18. The mathematical technique used to create high-resolution images by using the Earth's rotation to "fill in" a virtual large telescopes area is called aperture ________.

If a few telescopes stay in place while the Earth spins, then their positions relative to a star change over several hours; if we collect data during this time, the computer "synthesizes" or builds up a complete picture as if we had a full, solid mirror.

Explanation

If a few telescopes stay in place while the Earth spins, then their positions relative to a star change over several hours; if we collect data during this time, the computer "synthesizes" or builds up a complete picture as if we had a full, solid mirror.

Submit

19. Which physical property of light is most important for interferometry concepts to work?

Light travels in straight lines only

Light acts as a wave with peaks and troughs

Light has no mass

Light is always blue in deep space

Light can be turned into a solid

If light acts as a wave, then two waves can overlap and interfere with each other; if we can measure the timing of these wave peaks across different telescopes, then we can reconstruct a high-detail image using interference patterns.

Explanation

If light acts as a wave, then two waves can overlap and interfere with each other; if we can measure the timing of these wave peaks across different telescopes, then we can reconstruct a high-detail image using interference patterns.

20. The process of telescope array synthesis allows an group of small dishes to have the same resolving power as a single dish as wide as the distance between them.

True

False

If starlight or radio waves reach multiple telescopes at slightly different times, and if those signals are combined accurately, then the "effective aperture" becomes the maximum distance between the telescopes (the baseline), providing the same resolution as a massive single telescope.

Explanation

If starlight or radio waves reach multiple telescopes at slightly different times, and if those signals are combined accurately, then the "effective aperture" becomes the maximum distance between the telescopes (the baseline), providing the same resolution as a massive single telescope.

Building the Array: Telescope Array Synthesis Quiz

1. What are the main benefits of using virtual large telescopes?

2.

What first name or nickname would you like us to use?

2. Which of these factors would improve the "Synthesized Beam" (the quality of the image) in telescope array synthesis?

3. Why can't we just use one small telescope and magnify the image 1000 times instead of combining telescopes?

4. The use of virtual large telescopes that are located on different continents is called Very Long ________ Interferometry (VLBI).

5. Interferometry concepts state that if two telescopes are 100 meters apart, the system acts like a 100-meter-wide lens for resolution purposes.

6. How does the "correlator" help in combining telescopes?

7. Which of the following are challenges of aperture synthesis explained in high school physics?

8. In the context of interferometry concepts, what is "constructive interference"?

9. The "Event Horizon Telescope," which took the first photo of a black hole, is a global telescope array ________.

10. To succeed in telescope array synthesis, the signals from each telescope must be synchronized to a fraction of a wave cycle.

11. What is the primary purpose of combining telescopes into an array?

12. Which of the following is a famous example of combining telescopes to study the universe?

13. What happens to the "resolving power" of a system when the telescopes are moved further apart?

14. In interferometry concepts, the physical distance between the two furthest telescopes in an array is known as the ________.

15. Virtual large telescopes created through an array collect as much total light as a solid mirror of the same diameter.

16. Why is aperture synthesis explained more often in radio astronomy than in optical (visible light) astronomy?

17. Which of the following are necessary components for telescope array synthesis?

18. The mathematical technique used to create high-resolution images by using the Earth's rotation to "fill in" a virtual large telescopes area is called aperture ________.

19. Which physical property of light is most important for interferometry concepts to work?

20. The process of telescope array synthesis allows an group of small dishes to have the same resolving power as a single dish as wide as the distance between them.