Apparatus and Setup
This lab tabulates and compares real SILSO-sourced sunspot-number data across Solar Cycles 24 and 25 (Lecture 03), then computes the thin flux-tube pressure-balance fraction for a range of real sunspot field strengths (Lecture 04).
Materials and Data
| Cycle | Metric | Value | Date |
|---|---|---|---|
| Solar Cycle 24 | Smoothed max SSN | 116.4 | April 2014 |
| Solar Cycle 25 | Smoothed min SSN | 1.8 | December 2019 |
| Solar Cycle 25 | Smoothed max SSN | 160.8 | October 2024 |
| Solar Cycle 25 | Not-smoothed max SSN | 216 | August 2024 |
Cycle 25 figures live-verified this session (SILSO/WDC-SILSO via Wikipedia's "Solar cycle 25" article); Cycle 24 figure is a standard published value not independently re-verified this session (level 2; see ../reference-log.md). Sunspot umbral field: B=2800 G (Solanki 2003, level 2). Photospheric gas pressure: P_phot=12,500 Pa (level 2).
Procedure
- Compute the ratio of Solar Cycle 25's smoothed maximum SSN to Solar Cycle 24's, and state whether Cycle 25 is stronger or weaker.
- Compute the ratio of Cycle 25's not-smoothed to smoothed maximum SSN, and discuss what physical effect (short-term variability vs the underlying multi-month trend) this ratio reflects.
- Compute the sunspot magnetic pressure P_mag=B^2/(2 mu0) for the given real field strength and confirm it matches Lecture 04's stated value.
- Compute P_mag for three additional real, smaller sunspot field strengths (1500 G, 2000 G, 2500 G) and tabulate the pressure-balance fraction P_mag/P_phot for all four field strengths, identifying the threshold field strength at which the fraction first exceeds 1.0.
Analysis and Uncertainty
Discuss why the sunspot-number ratio comparison (Cycle 25 vs Cycle 24) should not be used to conclude anything about future Cycle 26, given the disclosed unpredictability of solar-cycle amplitude discussed in Lecture 03.
Deliverables
- The Cycle 24/25 ratio computations and interpretation.
- The four-field-strength pressure-balance table with the threshold field strength identified.
Assessment Criteria
- Correct ratio arithmetic for both cycle comparisons.
- Correct P_mag arithmetic (B in Tesla, not Gauss, inside the formula) for all four field strengths.
- Correctly identified threshold field strength.
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.
- Solar Cycle 25 sunspot numbers: live-verified this session (SILSO/WDC-SILSO); Solar Cycle 24 and sunspot field strength: standard published, level 2; see
materials/ASTR370/reference-log.md. - Generated by
materials/ASTR370/src/generate_astr370_content.py.