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Chapter 3

PSY397H1 Chapter Notes - Chapter 3: Cyanobacteria

Course Code
Martin Ralph

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Biological Rhythms
Chapter 3: Physical and Biological Time
The period of 24h represents the time required by the earth to complete one full rotation.
The earth makes one complete rotation on its axis in about 23h and 56 min.
Both the rotation of the earth and its revolution around the sun occur in a
counterclockwise direction
The Day
After a span of about 23h and 56min the earth has made one complete rotation on its axis
and the transit dial again reads 0 degrees for the reference star. However, the angle for the
position of the sun is only 44 degrees (though it is assumed that the angle for the position
of the sun is 45 deg from 0). The original 45 degrees will not be reached until one more
degree of rotation has occurred. This will require about 4 more minutes = 24 HOUR IN A
- as a result, the location of the earth relative to the sun has changed by about 1
The Year
The seasons are based upon the revolution of the earth around the sun
The earth is closest to the sun in January and furthest in july.
The Month
Tidal rhythms are controlled in large measure by the movements of the Moon. The moon
revolves around the earth, completing one full revolution in about 27.25 days = the
sidereal month
Because the average female menstrual cycle is about 29.5 ± 3 days, a series of spans
between full moons may have provided primitive women with a time measure for the
length of a pregnancy.
- Egyptians based their predictions on year length upon the season flooding of the
Nile River and the accompanying annual reappearance of the Dog Star.
The Week
It is likely that the 7 day week was being followed by the jews during the time of Moses,
based upon their belief that God worked for 6 days, and rested on the 7th day.
- Names for the days of the week have been derived from various sources,
including the names of planets, names of mythical characters, or a combination of
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