An eclipse is an astronomical
event that occurs when one celestial object moves into the
shadow of another. Eclipses page is a guide to
eclipses: total, partial, annular and lunar.
Just as the Moon cases a shadow
through space, so does the Earth. A Lunar Eclipse occurs when
the Moon passes through the shadow of our planet and can only
happen during a Full Moon when it is directly opposite the sun
in our skies.
There are three types of lunar
Penumbral Lunar Eclipse is when the Moon passes
through the Earth penumbral shadow. These events usually pass
un-noticed, as the effect of the shadow is subtle and difficult
Partial Eclipse is seen when the Earth's umbra shadow
falls on part of the lunar surface and is easily visible.
3. In a
Total Eclipse the entire of the Moon is engulfed in
the umbra shadow and takes on vibrant colours as sunlight is
filtered through Earth's atmosphere.
The colour of the Moon during a
lunar eclipse is often described as blood red, but its exact
appearance often depends on how much dust and clouds are present
in Earth's atmosphere. Dust from major volcanic eruptions can
tint the eclipse much darker. Unlike total solar eclipses which
are visible only from a narrow strip, lunar eclipses can be seen
across the entire night side of Earth.
Phrases and words
used to describe the events during a Total Eclipse of the Sun.
First Contact: When the Moon
starts its slide across the Sun's disc.
Second Contact: The Moon has
covered the entire Sun.
The Moon is moving off the Sun and part of the Sun's surface has
become visible once more.
The entire disc of the Sun is visible again as the Moon moves
The period when the entire disc of the Sun is obscured.
Seen from a location where the entire Sun is not covered by the
Photosphere: The bright
'surface' of the Sun.
Corona: The outer atmosphere
of the Sun.
The last beacons of sunlight seen through the hills and valleys
on the edge of the Moon.
Diamond Ring: The
effect created by the last (or first) bead of light from the
A solar eclipse
occurs when the Moon passes between the Earth and the Sun
casting a shadow through space that touches the planet's
surface. Unfortunately, although the Moon orbits the Earth every
29.5 days, there is not a solar eclipse every month because the
Moon's orbit is tilted by 5 degrees in relation to Earth's own
orbit around the Sun. This misalignment sends the Moon's shadow
off into space, missing the Earth, on most occasions. But at
least twice a year the orbits of the two bodies come into line,
casting the shadow upon our planet in one of nature's most
The Moon's shadow
is made of two parts, the penumbra and the umbra. The penumbra
is the faint outer part of the shadow. A partial eclipse is
visible where it falls on Earth. The umbra is the dark inner
part of the shadow and is typically about 160km across. Those
lucky enough to be along the track of this dark core will
witness a total eclipse of the Sun. At totality an eerie
darkness will fall across the land and the pearly-white halo of
the Sun's wispy outer atmosphere, the corona, will be visible.
In the darkened sky, planets and stars can be seen. The
experience last only a few minutes, but it is one never to be
annular eclipse occurs when the Sun and Moon are exactly in line,
but the apparent size of the Moon is smaller than that of the
Sun. Hence the Sun appears as a very bright ring.
The Moon's orbit
around the Earth is not a perfect circle. It cuts an oval track
through space that takes the Moon between 405,600km from Earth
at its maximum extent and 355,700km away at its closes approach.
As the distance from the Earth to the Moon varies so does the
apparent size of the Moon in our skies. When it is closer it
appears larger in the sky than the Sun and can completely
obscure the solar disc, but when it is further away its smaller
apparent size is not enough to cover the Sun. The umbral of the
shadow cannot reach the Earth instead a third portion of the
shadow is born: the antumbral or negative shadow. An annular
eclipse is visible where the antumbral sweeps across the Earth's
surface, this is known as the path of annularity. From within
this region the Moon's dark disc is centred on the sun, but
unable to obscure all its light, leaving a brilliant ring of
fire in the sky, Unfortunately, the Sun's corona is lost in the
glare of the annular eclipse.
What, Where, When, Why, and How Guide to Watching Solar and
Lunar Eclipses by Philip S. Harrington
pages 1 to 7, Astronomy Now Magazine, 2006.
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