Six Clocks in the Sky: A Compact Guide to Celestial Cycles

Goal Create a concise, source-backed comparison of six astronomical time cycles that are often confused with their nearest look-alikes. Deliverable Submit exactly one UTF-8 Markdown file named six_clocks_in_the_sky.md, between 650 and 1000 words and no larger than 20 KB. Observable requirements 1. Cover exactly these six cycles, each in its own clearly headed section: solar day, sidereal day, synodic month, sidereal month, tropical year, and sidereal year. 2. For every cycle, give a plain-language definition, an approximate duration with units and sensible precision, the reference frame or event that marks completion, and one original sentence explaining why it differs from its nearest look-alike. 3. Include one comparison table containing all six cycles with these columns: cycle, approximate duration, measured against, nearest look-alike. 4. Include one original monospace ASCII timeline or scale diagram inside a fenced text block. It must be at most 18 lines, include all six cycle labels, and say when it is schematic or not to scale. 5. Provide one working authoritative source URL per cycle, mapped clearly inline or in a source section. Suitable sources include NASA, IAU, IERS, USNO, NIST, or a university observatory or astronomy text. 6. Correctly explain the three contrasts: solar versus sidereal day, synodic versus sidereal month, and tropical versus sidereal year, without presenting approximate durations as exact constants. 7. Use stable facts and accessible language for a curious general reader. Negative scope No astrology or horoscopes, current sky events or ephemerides, navigation or safety advice, executable code, scripts or HTML, copied diagrams or source prose, paywalled-only sources, personal data, accounts, purchases, or outreach. Pass/fail acceptance gates - Exact filename, one Markdown file only, 650-1000 words, and 20 KB or smaller. - Exactly six required headed sections plus the six-row comparison table and one diagram of at most 18 lines. - Definitions, durations, reference frames, and the three pairwise contrasts are internally consistent and factually sound. - Six working authoritative source URLs are unambiguously mapped to the six cycles. - No prohibited content from the negative scope. Scoring rubric (100 points, in order) 1. Factual accuracy and source quality: 40 points. 2. Comparative explanation and plain-language clarity: 25 points. 3. Completeness, structure, and limit compliance: 20 points. 4. Diagram usefulness, craft, and originality: 15 points. Tie-breaker Prefer the submission whose durations, definitions, contrasts, and source mapping can be verified most directly; then prefer the clearer comparison. Voice and visual treatment of the diagram are creatively open outside the mandatory core.