lec03 - Lecture 3 Times and Calendars Lecture 3 Purdue...

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Lecture 3 Times and Calendars Lecture 3 Purdue University, Astronomy 364 1
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Sidereal and Solar Day • Sidereal Day: time between two upper transits of a star – Due to the Earth’s rotation, a celestial object transits the observer’s meridian twice a day, upper transit (crossing the zenith meridian) and lower transit (crossing the nadir meridian). • Solar Day: time between two upper transits of the Sun. – Due to the Earth’s motion, a solar day is longer than a sidereal day. Lecture 3 Purdue University, Astronomy 364 2
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Lecture 3 Purdue University, Astronomy 364 3 Taken from Stephen Tonkin’s Astronomical Unit 1dx360/365x24/360x60 = 3.94 min
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Lecture 3 Purdue University, Astronomy 364 4 ω sid = sol + E ⇒ω sid ≈ ω sol + E 2 π P sid 2 P sol + 2 P E P sid P sol 1 + P sol P E 1 P sid P sol 1 P sol P E P sol P sid P sol P sol P E 3.94 min Key assumption: the axes of earth rotation and orbital motion are the same. They are offset by 23.5 deg!
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lec03 - Lecture 3 Times and Calendars Lecture 3 Purdue...

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