Apparatus and Setup
This is a data-analysis lab using the Rayleigh-criterion resolution relation of Lecture 02 applied to five real telescopes' published apertures (Keck, HST, VLT, JWST, and a small amateur reflector). No telescope time is required.
Materials and Data
| Telescope | Aperture (m) | Reference wavelength | Rayleigh resolution (mas) |
|---|---|---|---|
| Keck I/II | 10.00 | V (551 nm) | 13.87 |
| Hubble Space Telescope | 2.40 | V (551 nm) | 57.77 |
| ESO Very Large Telescope (UT) | 8.20 | V (551 nm) | 16.91 |
| James Webb Space Telescope | 6.50 | 2.0 µm | 77.43 |
| amateur reflector | 0.20 | V (551 nm) | 693.28 |
Keck's aperture, collecting area, and focal length are live-verified this session (Wikipedia, "W. M. Keck Observatory," 2026-09-24); HST, VLT, and JWST apertures are standard published mission/facility specifications (level 2, see ../reference-log.md).
Procedure
- For each telescope in the data table, compute the Rayleigh-criterion angular resolution θ = 1.22λ/D at the stated reference wavelength, converting from radians to milliarcseconds, and confirm your value against the table.
- Compute the ratio of Keck's V-band resolution to the amateur telescope's V-band resolution, and state how many times finer Keck's diffraction limit is.
- Compute the ratio of the median atmospheric seeing (0.8″) to Keck's V-band diffraction limit, and state what this ratio means physically for an uncorrected (non-adaptive-optics) Keck image.
- JWST observes at 2.0 µm rather than V band because its primary science targets (distant galaxies, cool sources) emit most strongly in the infrared and because Earth's atmosphere, irrelevant for a space telescope, would otherwise block much of this range. Using JWST's and Keck's apertures and the wavelength ratio (2.0 µm vs. 551 nm), compute the ratio of their diffraction limits and state which is sharper.
Analysis and Uncertainty
State explicitly why the amateur telescope's poor diffraction-limited resolution is essentially irrelevant in practice: an uncorrected ground-based image is normally seeing-limited (Lecture 02), so the amateur telescope's real-world image quality is not much worse than Keck's uncorrected image quality, even though Keck's theoretical diffraction limit is dramatically finer.
Deliverables
- Completed resolution table with independently reproduced arithmetic for all five telescopes.
- The Keck-to-amateur and seeing-to-Keck ratio calculations with interpretation.
- The JWST-versus-Keck diffraction-limit comparison with a stated conclusion.
Assessment Criteria
- Correct unit conversions (radians to milliarcseconds) in all five resolution calculations.
- Correct ratio arithmetic and correctly stated direction (finer vs. coarser) for both ratios.
- Correct, quantitatively supported JWST-versus-Keck conclusion.
References and Provenance
- OpenStax Astronomy 2e (local reference copy: references/openstax-astronomy-2e-extracted.txt), Chapter 6 (astronomical instruments), descriptive only; this course exceeds that introductory treatment throughout.
- Keck aperture/collecting area/focal length: live-verified this session (Wikipedia, "W. M. Keck Observatory"); HST, VLT, JWST apertures: standard published mission/facility specifications, not independently re-verified this session; see
materials/ASTR340/reference-log.md. - Generated by
materials/ASTR340/src/generate_astr340_content.py.