Lab 05: Remote Sensing Geometry and Parker Solar Probe In-Situ Prediction

Apparatus and Setup

This lab works through a simplified schematic helioseismic-frequency reasoning exercise and a coronagraph field-of-view geometry calculation (Lecture 09), then uses Parker Solar Probe's real perihelion distance with Lecture 08's numerically solved wind-speed curve to predict the in-situ solar wind speed near its closest approach (Lecture 10).

Materials and Data

Parker Solar Probe: launched 2018-08-12, perihelion 9.86 R_sun (6.9e+06 km), record heliocentric speed 191 km/s (all live-verified this session). Parker critical radius (Lecture 08): r_c=4.62 R_sun.

Procedure

1. Compute PSP's perihelion distance in units of the Parker critical radius (r_perihelion/r_c), and state whether PSP samples plasma inside or outside the critical point.
2. Using Lecture 08's numerical transonic-solution solver, compute the predicted Parker-wind speed at PSP's exact perihelion distance.
3. Compare this predicted speed to PSP's own record heliocentric *orbital* speed (191 km/s) and explain explicitly why these are two different physical quantities that should not be numerically compared as if they were measuring the same thing.
4. Compute the coronagraph occulting-disk geometry: if an occulting disk must block a field of view out to 1.5 solar radii to fully hide the photospheric disk and its immediate surroundings, and the coronagraph's total field of view extends to 6 solar radii, compute what fraction of the coronagraph's total field of view is unusable due to the occulting disk.

Analysis and Uncertainty

Discuss why the simplified isothermal Parker wind model's speed prediction at PSP's perihelion is only an order-of-magnitude comparison point, not a precise prediction to be checked against PSP's actual in-situ SWEAP measurements, given the real corona's non-isothermal, magnetically structured nature (Lecture 08's disclosed limitation).

Deliverables

• PSP's r/r_c ratio and predicted Parker-wind speed at perihelion.
• The explicit orbital-speed-vs-wind-speed distinction discussion.
• The coronagraph field-of-view fraction calculation.

Assessment Criteria

• Correct r/r_c ratio and correct numerical Parker-wind solve at that ratio.
• Explicit, correct statement that orbital speed and wind speed are different physical quantities.
• Correct field-of-view fraction arithmetic.

References and Provenance

• OpenStax Astronomy 2e (local extracted reference copy: references/openstax-astronomy-2e-extracted.txt) covers the Sun in Chapter 15 ("The Sun: A Garden-Variety Star"): 15.1 The Structure and Composition of the Sun, 15.2 The Solar Cycle, and 15.3 Solar Activity above the Photosphere. Chapter 15’s section numbering was cross-checked directly against its own embedded figure numbering this session (Figures 15.1 through 15.24 all appear under their matching section headers with no offset), so this citation is verified against the local extracted text rather than extrapolated by analogy from a prior course. OpenStax’s treatment throughout Chapter 15 is descriptive and qualitative; nearly every quantitative derivation in this course (the hydrostatic solar-atmosphere/scale-height argument, the sunspot magnetic-pressure balance, the Parker solar-wind critical-point argument and its numerical transonic solution, flare free-energy budgets, the Chapman-Ferraro magnetopause standoff distance, and the Dessler-Parker-Sckopke ring-current/Dst relation) goes well beyond OpenStax Astronomy 2e’s introductory level; each lecture states explicitly where this course extends beyond the assigned reading.
• Parker Solar Probe mission facts: live-verified this session; see materials/ASTR370/reference-log.md.
• Generated by materials/ASTR370/src/generate_astr370_content.py.