1. Rotation, Orbit, Eclipse “Seasons” And the Annular Eclipse
Lunar Motions
Rotation, Orbit,
Eclipse “Seasons”
And the Annular Eclipse

2. Synchronicity
The Period of the Moon’s revolution and its rotation are the same.
We say that the Moon has synchronous revolution & rotation
As a result one side of the Moon is always facing the Earth (the near-side) and one away (the far–side) even though the Moon does rotate.

3. Orbit Size and Shape
The Moon orbits at an average of 380,000 km from earth.
Its orbit is elliptical. The nearest point is called Perigee.
The Farthest point is called Apogee.
The apparent size of the Moon appears to vary from its average size by about 15%
The Moon’s orbit is tilted 5° from Earth’s Orbit
This 5° tilt is why we don’t have eclipses each month.
Because of it the Moon is usually not on the ecliptic, and can be as much as 5° from it

4. The Tilt of the Moon’s Orbit and Eclipse Seasons
Due to the 5° tilt of the moon’s orbit…
the Moon-Earth-Sun do not line up the right-way to have Eclipses every month.
They only line-up right twice a year. (Syzygy)
So each year there are two periods, each two weeks long, when the eclipses occur
These are called Eclipse Seasons, they are about Six Months apart
During 2016 they are in March and September.

5. The Shadow of a Planet or a Moon
The shadow of a planet or moon has three parts
The Umbra, Penumbra and Antumbra
The Umbra, or true shadow, where no light from the Sun reaches
If an object is in the umbra
It will look dark
From it the Sun will be totally blocked (eclipsed)

6. From the object The center of the Sun is blocked (An annular eclipse)
The Penumbra, or partial shadow, some but not all the light reaches it.
An object in the penumbra appears dimly lit
From the object the Sun appears
…With a piece ‘bitten out’
(A partial eclipse)
The Antumbra, another partial shadow, but behind the Umbra
An object in the antumbra appears dimly lit
From the object The center of the Sun is blocked (An annular eclipse)

7. Solar Eclipse Is when the Moon casts its shadow on the Earth.
Because the Moon is smaller than the Earth only a part of the Earth experiences an eclipse.
A Total Solar Eclipse is visible only to a narrow line of places on Earth where the umbra falls
In a Total Solar Eclipse the Sun is completely blocked by the Moon and the Corona and Chromosphere becomes visible.
Places where the penumbra falls see a Partial Solar Eclipse

9. An Annular Eclipse
Sometimes when a Solar Eclipse should happen the Moon is at its Farthest point.
The Umbra is not long enough to reach the Earth so…
The Moon doesn’t cover all the Sun, only the center leaving a bright ring around it.
This is an Annular Eclipse

11. When Can Eclipses Happen?
It is when the moon is on the ecliptic that an eclipse can happen
A Solar Eclipse can only happen during a New Moon
A Lunar Eclipse can only happen during a Full Moon
Lunar and Solar Eclipses therefore happen about two weeks apart.