General Science 2310 - Moon Phases and Tides

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SPATIAL RELATIONSHIPS BETWEEN THE EARTH, SUN, AND MOON

Excellent Online lectures on these topics can be found at :

Astronomynotes.com: Naked Eye Astronomy

University of Alberta: Lunar Phases and Eclipses

Indiana State University: The Moon

Phases of the Moon

Phases of the moon are a consequence of its spherical shape and our viewing it from various angles relative to the light source (the Sun)
We always have almost the same face of the Moon facing us at all times (the man in the Moon.)
The lunar month begins with a New Moon which we can't see because it is so close to the Sun (this is the time for Solar eclipses)
During week one we see a waxing crescent moon which appears as crescent shape getting fatter every day.
At the end of week one we see the first quarter moon which looks like exactly half a circle in the sky.
During week two we are in the waxing gibbous phase during which the moon appears to be not quite full but getting fuller every day.
At the end of week two we have a full moon which appears as a complete disk in the sky

Phases of the Moon

Week	Phase	After Sunset	Before Sunrise	Rising Time
Week 1	Waxing Crescent	Towards the West	Not seen	after Sunrise
Week 2	Waxing Gibbous	Towards the South	Not seen	after Noon
Week 3	Waning Gibbous	Not Seen	Towards the South	after Sunset
Week 4	Waning Crescent	Not Seen	Towards the East	after Midnight

Tides

A tidal force is the part of a gravitational force on a body that gives rise to deformations or stresses on that body. Tides arise because gravity varies with distance.
For instance, if you were falling feet first into a black hole, the gravitational force on your feet would be so much greater than the force on your head that you would be deformed into a spaghetti - like strand .
The bulges of water that we most commonly call tides are a consequence of the water closest to the moon being attracted to a greater degree than is the solid mass of the Earth, which is itself attracted to a greater degree than is the water furthest from the Moon.
High tide will occur at a particular point on the Earth's surface when the Moon is crossing the meridian ( closest to that point on the Earth ) and when the Moon crosses the line 180 degrees from the meridian ( farthest away ).
It takes 12 hours and 25 minutes for a particular point on the Earth to move between two high tides. The extra 25 minutes arises since the Moon revolves around the Earth in the same sense that the Earth Spins.
Therefore high tide occurs 50 minutes later every day.
The Sun's gravity also has an effect on tides on Earth, this effect is smaller than that of the Moon. Although the Gravitational force from the Sun is ~200 times stronger than that from the Moon, it is the difference in Gravitational force between the near and far sides of the Earth that give rise to the tidal force. The tidal force from the Moon is slightly more than twice as great as the tidal force from the Sun.
The tidal effects of the Sun and the Moon are working together at new Moon and at Full Moon. The magnitude of the tides are greatest at these times. These are known as Spring tides.
The tidal effects of the Sun and the Moon are working against each other at first and third quarter Moon. The magnitude of the tides are least at these times. These are known as Neap tides.
The measured high of the tides varies greatly over the surface of the Earth ( The Bay of Fundy has the highest tides in the world .) This variation is completely a product of geomorphology having little to do with astronomy.

To contact the instructor please email to:

wwall@gale.lakeheadu.ca