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August 29, 2011: 10am Class. On-line Quiz #1 on d2l: Please complete before class on Friday, Sept. 2 HW 2 on line (d2l and boojum ): Create a Constellation Due Wednesday, Sept. 7, in class. Honors Section 3H: Please complete doodle poll (see Megan’s email and class web site)

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august 29 2011 10am class
August 29, 2011: 10am Class
  • On-line Quiz #1 on d2l:
    • Please complete before class on Friday, Sept. 2
  • HW 2 on line (d2l and boojum): Create a Constellation
    • Due Wednesday, Sept. 7, in class.
  • Honors Section 3H: Please complete doodle poll
  • (see Megan’s email and class web site)
  • When you go to Mt. Lemmon, bring a flashlight.
  • Today: Precession, Phases of the Moon, Eclipses,
    • Seasons
a spinning top precesses
A spinning top “precesses”

http://en.wikipedia.org/wiki/Precession

precession1
Precession
  • The Earth’s axis of rotation precesses, so makes a
    • big circle, with a period of 26,000 years
  • (so it goes once around every 26,000 years)
  • The Earth’s pole moves about one degree in 72 years.
  • The precession is a result of the fact that the Earth’s
  • axis of rotation is tilted with respect to the ecliptic,
  • and with respect to the orbit of the Moon.
  • The Moon’s and Sun’s gravity tug on the Earth and
  • cause the pole to precess.
slide5

Currently the North Celestial Pole is very near the North Star, Polaris.

  • In 3000 BC, the pole star was Thuban, in the constellation Draco.
  • But it is moving away from Polaris:
    • in 14000 AD, it will be pointed towards Vega, as it was in 12000 BC
  • Polaris will be the North Star again in 27800 AD.

Direction of the North Celestial

Pole as a function of year, AD

slide6

Direction of the South Celestial

Pole as a function of year, AD

hipparchus of rhodes 190 bc 120bc
Hipparchus of Rhodes (190 BC-120BC)
  • Precession was first observed by Hipparchus
  • Also was “father” of trigonometry
  • Made one of the first star catalogs
the moon

The Moon

Phases and Eclipses

slide9

We always see the SAME SIDE of the Moon because the moon orbits the Earth and rotates on its axis with EXACTLY the same period (29 ½ days).

The “DARK SIDE OF THE MOON” was not seen by any human until spacecraft

were sent to the moon and photographed it, in the 1950s.

slide11

Near Side of the Moon

Far side of the Moon

slide14

The Moon appears to go through a series of PHASES during each month: new moon, crescent, gibbous, full, gibbous, crescent, new.

Phases of the Moon youtube.com rap.

slide20

Solar Eclipses:

Total

Partial

Annular