AST 115 1st Edition Lecture 4Outline of Last Lecture I. Measuring latitudeII. Circumpolar starsIII. Seasonsa. Earth’s tiltIV. Phases of the Moona. Causesb. Phases on other planetsV. View of the Earth from the surface of the MoonVI. Synodic vs. SiderealVII. Introduction to measuring timeOutline of Current Lecture I. Measuring time continuedII. Calendarsa. Types of calendarsIII. PrecessionIV. Introduction to eclipsesCurrent Lecture Measuring time continued:o Central Daylight Time: CDT = CST + 1 houro Time Standards GMT = UTC (Coordinated Universal Time) Calendarso Many civilizations produced a variety of calendars (Maya, Aztec, Anasazi) to keep track of the seasons.o Main problem when creating a calendar = there is not an exact number of days per year (spins per orbit). 1 “year” = 365.24279 “days” o The Simple Calendar 365 days Problem: would find seasons falling behind it by about 1 day in just 4 years.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Julian Calendar Invented by Julius Caesar (45 B.C.) In an attempt to make the calendar more accurate, he added a leap day to every 4th year (divisible by 4). This gave an average of 365.25 days per year.o Gregorian Calendar Invented in 1582 by Pope Gregory XIII to fine tune the Julian calendar. There was one rule to the calendar: century years (years that end in 00) are leap years only if it is divisible by 400. This gave the calendar an average of 365.2425 days per year Problem: there was an accumulated error where 10 days were omitted from the calendar and people were mad. Precessiono Precession: Earth’s rotational axis slowly turns in space. This takes about 26,000 years for one cycle.o Discovered by Hipparchus about 2000 years ago.o Due to the gravity of the Moon interacting with the spinning of the Earth.o Precession causes a change in the position of the NCP (and SCP) among the stars and thus, a change in the polar star.o Does NOT cause a change in the occurrence of the seasons. Eclipseso Eclipses do not occur at each new and full phase of the Moon. This is due to the 5˚ tilt of the Moon’s orbital plane with respect to the ecliptic plane.o Eclipses occur 2 times each year during “eclipse seasons”. These intervals move through the calendar and occur slightly earlier each
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