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The Moon does not have its own light, but shines because
its surface reflects the Sun's rays.
Eclipses of the Moon happen when the Sun, Earth and
Moon are aligned to form an almost or exact straight line.
The technical term for this is syzygy, which comes from the
Greek word for being paired together.
Why do Total Lunar Eclipses happen?
During a Total Lunar Eclipse, the Sun, Earth and Moon form
a straight line. The Earth blocks any direct sunlight from
reaching the Moon. The Sun is behind the Earth, so the
Sun's light casts the Earth's shadow on the Moon. This
shadow covers the entire Moon and causes a Total Lunar
Eclipse.
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Earth's Three Shadows
The Earth's shadow can be divided into three
parts:
Penumbra - the outer part.
Umbra - darker, central part.
Antumbra - a partly shaded area beyond the
umbra.
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Sun, Earth and Moon Aligned
For a lunar eclipse to occur, the Sun, Earth and
Moon must be roughly aligned in a straight line. If
the Sun, Earth and Moon do not align, the Earth
cannot cast a shadow on the Moon's surface and
an eclipse cannot happen.
When the Sun, Earth and Moon are not perfectly
aligned, only the outer part of the Earth's shadow
covers the Moon. Such an eclipse is called
a penumbral lunar eclipse. In a Total Lunar Eclipse,
the Earth's umbra completely covers the Moon.
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Phases of the Moon
Moon phases depend on the position of both the
Sun and Moon with respect to the Earth.
The 4 primary phases of the Moon are: new, first
quarter, full and third quarter (last quarter).
The intermediate phases between the primary
phases are, waxing crescent (new crescent),
waxing gibbous, waning gibbous, and waning
crescent (old crescent).