Your vessel is at the equator at midnight on 1 January, and a star is observed rising. At what time will this same star rise on 1 February, assuming your vessel's location is still at the equator?
• Sidereal day vs. solar day – how much earlier a star rises each night compared to the Sun • Approximate number of minutes a star’s rising time shifts per day • Total number of days between 1 January and 1 February and how that affects cumulative time shift
• First, recall roughly how many minutes earlier a given star rises each successive night due to Earth’s orbit around the Sun. Write that number down. • Next, multiply that per-day change by the number of days between the two dates. Convert that product into hours and minutes. • Finally, subtract this total time difference from midnight (0000) and see which answer choice is closest to the resulting rising time.
• Be sure you are using the shift for a sidereal day (stellar time), not for the Sun’s 24-hour solar day. • Confirm the number of days you should use between 1 January and 1 February (inclusive or exclusive?) as typically used in navigation problems. • After finding the total minutes shift, double-check your time conversion into HHMM format to avoid simple arithmetic mistakes.
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