# Telescopes, resolution and observing data

> A telescope collects light over an aperture. In a simple unobstructed comparison, collected power scales with diameter squared.

Course: [Space and astronomy foundations](https://studybrix.com/en/courses/space-and-sky-foundations/index.md)
Level: school
Prerequisites: Areas, ratios and measurement uncertainty.

## Notes

### Aperture

A telescope collects light over an aperture. In a simple unobstructed comparison, collected power scales with diameter squared.

### Resolution

Angular resolution differs from magnification. Diffraction gives a characteristic angle proportional to wavelength divided by aperture diameter.

### Noise

Longer exposures can improve signal-to-noise in appropriate regimes, but detector noise, backgrounds, saturation and moving targets complicate the tradeoff.

### Calibration

Dark frames, flats and reference observations address different measurement effects. A processed image should preserve records of its transformations.

## Practice questions

### 1. Two unobstructed circular telescopes have diameters D and 2D. Find the collecting-area ratio of the larger to the smaller.

Answer: 4

Explanation: Area scales with diameter squared.

### 2. What is angular resolution?

A. Only telescope weight
B. The same as display zoom
C. Ability to distinguish close directions
D. Only image brightness

Answer: Ability to distinguish close directions

Explanation: Resolution concerns distinguishable angular separation.

### 3. At fixed aperture, shorter wavelength gives what diffraction-limited angular scale?

A. No dependence ever
B. A smaller angle
C. A larger angle necessarily
D. An infinite angle

Answer: A smaller angle

Explanation: The characteristic diffraction angle scales as λ/D.

### 4. For a simplified photon-limited model SNR=sqrt(N), find SNR for N=400 detected signal photons with negligible background.

Answer: 20

Explanation: sqrt(400)=20 under the stated assumptions.

### 5. Can enlarging a blurry image always reveal genuine new resolved detail?

A. Yes, with any zoom
B. No
C. Only if the file name changes
D. Yes, if the monitor is larger

Answer: No

Explanation: Magnification does not reverse lost resolution by itself.

### 6. Why should an observing report record exposure and calibration choices?

Sample answer / marking guidance: They affect noise, background, saturation and interpretation. Reproducible processing requires this context.

Explanation: Credit measurement effects and reproducibility.

### 7. Give one reason a space telescope and a ground telescope can offer complementary evidence.

Sample answer / marking guidance: Atmospheric transmission and turbulence affect ground observations, while instrument wavelength coverage and operating constraints differ. Combining suitable measurements can reduce ambiguity.

Explanation: Credit a relevant physical distinction without claiming all space telescopes outperform all ground telescopes.

### 8. If collected signal counts quadruple in the stated negligible-background photon model, by what factor does SNR change?

Answer: 2

Explanation: SNR scales as square root of signal counts in that model.

## Further reading

- https://science.nasa.gov/mission/hubble/science/telescopes-101/

Original AI-assisted educational draft; not independently teacher-reviewed. References support further study, not copied exercises, affiliation or curriculum accreditation.