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Transcript of Announcements Homework Set 1 is due today Homework set 2: Chapter 2 # 45, 46, 50, 52, 53 & 54 Use...
![Page 1: Announcements Homework Set 1 is due today Homework set 2: Chapter 2 # 45, 46, 50, 52, 53 & 54 Use Exam Formula Sheet as you do the homework to familiarize.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfe5503460f949cf69f/html5/thumbnails/1.jpg)
Announcements•Homework Set 1 is due today
•Homework set 2: Chapter 2 # 45, 46, 50, 52, 53 & 54
•Use Exam Formula Sheet as you do the homework to familiarize yourself with where things are on it.
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Hint for homework problems # 52, 53 & 54
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Terrestrial CoordinatesLongitude is measured CCW (+) or CW (-) around from Greenwich England
Latitude is measured North or South of the equator
Both are measured in degrees, minutes and seconds
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Celestial CoordinatesThe angle between the celestial equator and the ecliptic is 23.5°
Right Ascension (RA) is measured CCW from the Vernal Equinox and is in hours, minutes and seconds
Declination (Dec) is measured above (+) or below (-) the celestial equator and is in degrees, minutes and seconds
See Appendix A6 for more on celestial coordinates
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Finding the CE and NCP at your latitude
Altitude of NCP above due north horizon along the meridian is just f, your latitude (+ for north, - for south)Altitude of the celestial equator above due south horizon along the meridian is 90°-f
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ExampleChapter 2 problem # 43: The Moon’s orbit is tilted by about 5° relative to the Earth’s orbit around the Sun. What is the highest altitude in the sky that the Moon can reach, as seen in Philadelphia (latitude 40° North)?
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Example SolutionWhat is being asked?...Maximum altitude of the Moon from 40° North latitude.
What information is given?...latitude = 40° N
Tilt angle of Moon from ecliptic = 5°Tilt angle of ecliptic from celestial
equator = 23.5°
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Example Solution 2Equation(s) to use: Refer to diagram two slides back. The altitude of the celestial equator above the local horizon is 90° - Latitude
CE = 90° - 40° = 50°
Maximum altitude of Ecliptic = CE + 23.5° = 50° + 23.5° =
73.5°
Maximum altitude of Moon = EclipticMax + 5°
= 73.5° + 5° = 78.5°
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Time and AstronomyThe 24 Hour Day?
One rotation of Earth = 1 sidereal day
23 hours 56 minutes 4.091 secondsThis is the time required for the
Earth to complete one rotation with respect to the fixed stars
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As the Earth rotates it also moves around
the Sun.
So, for the Sun to return to the same place in the sky the Earth must rotate a little more than one complete rotation
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Noon–to–noon isn’t always 24 hours
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The Mean Solar Day is exactly 24 hours. It is the time between meridian transits of the Sun averaged over four years
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The Year
1 orbit around the Sun = 365.2564 days The sidereal year
1 Tropical Year = 365.2422 mean solar days The time from Vernal equinox to Vernal equinox
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Pope Gregory XIII’s CalendarThe Gregorian Calendar (1582)
Most years have 365 days
Years evenly divisible by 4 have 366 days except century years.
Only century years evenly divisible by 400 are leap years
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Precession of the Equinox
Like a spinning gyroscope, the Earth precesses. The period of the precession is 25,920 years
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The Precession of the Equinox leads to a shift of the celestial
pole
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It also shifts the constellations of the zodiac
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The Lunar CycleSidereal versus Synodic
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The sidereal period is
the orbital period with respect to the “fixed”
stars: 27.32166
days
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The Synodic period is the length of the cycle of phases
29.530589 days
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Since the angular size of the Sun and Moon are almost the
same, eclipses occur
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The Saros Cycle is an eclipse cycle
223 Synodic Months or 18 years 11.3213 days
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The Saros Cycle is the repetition cycle of eclipse