Gravitational Lensing Observations Quiz: Test Your Astronomy

11th Grade

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By Thames

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Quizzes Created: 10017 | Total Attempts: 9,652,179

| Attempts: 11 | Questions: 20 | Updated: Mar 13, 2026

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1. When a quasar is strongly lensed into multiple images, the images can:

Always arrive at the same time

Vary in brightness at different times due to different travel times

Lose all colour information

Stop emitting light

Concept: time delay lensing. Different light paths have different lengths and pass through different gravitational potentials. That can create measurable time delays between image brightness changes.

Explanation

Concept: time delay lensing. Different light paths have different lengths and pass through different gravitational potentials. That can create measurable time delays between image brightness changes.

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About This Quiz

Gravitational Lensing Observations Quiz: Test Your Astronomy - Quiz

This assessment explores gravitational lensing, a phenomenon where massive objects like galaxies bend light from distant stars. It evaluates your understanding of key concepts such as the physics behind lensing, its observational techniques, and implications for cosmology. Engaging with this content is essential for anyone interested in astronomy, as it... see moreenhances comprehension of how we observe the universe and the role of gravity in shaping our view of distant celestial bodies. see less

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

You may optionally provide this to label your report, leaderboard, or certificate.

2. Lensed images can show the same intrinsic variability (like quasar flickering) but shifted in time.

True

False

Concept: matched variability. If the source varies, each image repeats the pattern after a delay. This is a strong clue the images come from one source.

Explanation

Concept: matched variability. If the source varies, each image repeats the pattern after a delay. This is a strong clue the images come from one source.

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3. A key reason for time delays in lensing is:

The telescope clock runs slow

Light follows different paths and experiences different gravitational time effects

Light changes into sound

Stars change colour

Concept: path + gravity delay. There’s a geometric difference in path length and a gravitational contribution (often described as 'shapiro-like' delay). Together they shift arrival times.

Explanation

Concept: path + gravity delay. There’s a geometric difference in path length and a gravitational contribution (often described as 'shapiro-like' delay). Together they shift arrival times.

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4. A lensed quasar with repeated brightness patterns in multiple images suggests the images share the same ______.

Concept: common source identification. Matching patterns are hard to explain by coincidence. Time-shifted repetition strongly indicates a single background object.

Explanation

Concept: common source identification. Matching patterns are hard to explain by coincidence. Time-shifted repetition strongly indicates a single background object.

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5. What can lensing time delays help constrain (qualitatively)?

The boiling point of water

The mass distribution of the lens and cosmic distance scale

The charge of photons

The speed of sound in space

Concept: time delays as a probe. Time delays depend on lens mass distribution and geometry. With good models, they can inform cosmological distance-related parameters.

Explanation

Concept: time delays as a probe. Time delays depend on lens mass distribution and geometry. With good models, they can inform cosmological distance-related parameters.

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6. Measuring time delays requires monitoring brightness over time, not just taking one picture.

True

False

Concept: time-series data. Time delays are a timing measurement, so you need light curves. Single snapshots can’t reveal delays.

Explanation

Concept: time-series data. Time delays are a timing measurement, so you need light curves. Single snapshots can’t reveal delays.

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7. “Einstein ring” images are most likely to come from:

Very poor alignment

Near-perfect alignment

A lack of gravity

A sound wave

Concept: ring condition. Rings require strong symmetry and alignment. Slight offsets produce arcs rather than a complete ring.

Explanation

Concept: ring condition. Rings require strong symmetry and alignment. Slight offsets produce arcs rather than a complete ring.

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8. In strong lensing, why might one image be much brighter than another?

The source changes colour

Different paths have different magnifications due to lens geometry

One image is 'fake'

The speed of light differs between images

Concept: unequal magnification. Lensing magnification varies with position relative to the lens mass distribution. So images can have very different brightness.

Explanation

Concept: unequal magnification. Lensing magnification varies with position relative to the lens mass distribution. So images can have very different brightness.

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9. Small clumps of mass in the lens can slightly alter image brightness or details.

True

False

Concept: substructure effects. Tiny mass concentrations can perturb the lensing map. This can change flux ratios or create small distortions.

Explanation

Concept: substructure effects. Tiny mass concentrations can perturb the lensing map. This can change flux ratios or create small distortions.

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10. A practical observational difficulty in strong lensing is that:

Gravity stops light completely

The lens galaxy’s own light can overlap the lensed images

Light has no wavelength

Telescopes can’t see galaxies

Concept: foreground contamination. The lens can be bright and sits in front of the lensed images. Astronomers often subtract the lens light to study the arcs.

Explanation

Concept: foreground contamination. The lens can be bright and sits in front of the lensed images. Astronomers often subtract the lens light to study the arcs.

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11. A set of multiple images produced by a lens is sometimes called a lensed image ______.

Concept: lensing systems. Astronomers model each system by fitting image positions, shapes, and brightness. These systems constrain lens mass.

Explanation

Concept: lensing systems. Astronomers model each system by fitting image positions, shapes, and brightness. These systems constrain lens mass.

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12. If a lens produces four images of the same source, that pattern is often called:

A doublet

A quad

A single

A prism

Concept: common configurations. 'Double' (two images) and 'quad' (four images) are standard lensing terms. The exact number depends on alignment and mass shape.

Explanation

Concept: common configurations. 'Double' (two images) and 'quad' (four images) are standard lensing terms. The exact number depends on alignment and mass shape.

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13. The lens mass distribution (how spread out the mass is) affects both image positions and time delays.

True

False

Concept: model dependence. Mass distribution sets deflection angles and gravitational potential. That influences where images appear and how long light takes.

Explanation

Concept: model dependence. Mass distribution sets deflection angles and gravitational potential. That influences where images appear and how long light takes.

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14. Which observation most strongly confirms two bright spots are lensed images of one quasar?

They have different spectra

They share the same spectral features and show matching variability with a time shift

They are the same brightness

They are the same colour only

Concept: identification checks. Matching spectra show a common source, and time-shifted variability is an especially strong signature. Equal brightness is not required.

Explanation

Concept: identification checks. Matching spectra show a common source, and time-shifted variability is an especially strong signature. Equal brightness is not required.

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15. What data can help build a strong lens model?

Image positions

Arc shapes/orientations

Time delays (if variable source)

The lens’s music frequency

Concept: constraining models. Positions and shapes constrain deflection and shear. Time delays add information about the gravitational potential and geometry.

Explanation

Concept: constraining models. Positions and shapes constrain deflection and shear. Time delays add information about the gravitational potential and geometry.

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16. Lensing can act like a 'cosmic telescope,' improving resolution and brightness for very distant galaxies.

True

False

Concept: natural telescope. Strong lensing can magnify tiny, distant galaxies. It can reveal details that are otherwise below telescope resolution limits.

Explanation

Concept: natural telescope. Strong lensing can magnify tiny, distant galaxies. It can reveal details that are otherwise below telescope resolution limits.

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17. If the source is extended (like a galaxy), strong lensing is more likely to show:

A single dot only

Arcs and stretched structures

Only a brightness flicker

No distortion

Concept: extended sources. Extended objects get stretched into arcs because different parts of the source map to different image positions. Point-like sources often produce compact multiple images.

Explanation

Concept: extended sources. Extended objects get stretched into arcs because different parts of the source map to different image positions. Point-like sources often produce compact multiple images.

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18. Which is a correct statement about lensing and gravity?

Lensing requires the lens to emit light

Lensing depends on gravitational field, so dark matter can lens too

Lensing works only for radio light

Lensing changes the speed of light in vacuum

Concept: gravity-only requirement. Lensing cares about mass distribution, not luminosity. Dark matter contributes strongly because it has gravity.

Explanation

Concept: gravity-only requirement. Lensing cares about mass distribution, not luminosity. Dark matter contributes strongly because it has gravity.

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19. Time delay lensing is one example of how lensing provides information beyond 'pretty pictures.'

True

False

Concept: quantitative lensing. Time delays turn lensing into a measurable timing experiment. That adds constraints on mass models and distances.

Explanation

Concept: quantitative lensing. Time delays turn lensing into a measurable timing experiment. That adds constraints on mass models and distances.

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20. Grade 11 wrap-up (less obvious): If two images of a variable quasar show the same 'flicker pattern' but one repeats 12 days later, the best interpretation is that:

The quasar has two independent engines

You are seeing the same source via two lensing paths with a measurable time delay

The telescope recorded the data wrongly

The speed of light changed between days

Concept: time-delay signature. A repeated variability pattern with a fixed lag is a classic lensing clue. Different paths and gravitational delays make the same source appear at different times.

Explanation

Concept: time-delay signature. A repeated variability pattern with a fixed lag is a classic lensing clue. Different paths and gravitational delays make the same source appear at different times.

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