June 2011 total eclipse
Schematic diagram of
the shadow cast by the Earth. Within the central umbra shadow, the
Moon is totally shielded from direct illumination by the Sun. In
contrast, within the penumbra shadow, only a portion of sunlight is
A lunar eclipse occurs when the Moon passes behind the Earth so that
the Earth blocks the Sun's rays from striking the Moon. This can
occur only when the Sun, Earth, and Moon are aligned exactly, or
very closely so, with the Earth in the middle. Hence, a lunar
eclipse can only occur the night of a full moon. The type and length
of an eclipse depend upon the Moon's location relative to its
orbital nodes. Unlike a solar eclipse, which can only be viewed from
a certain relatively small area of the world, a lunar eclipse may be
viewed from anywhere on the night side of the Earth. A lunar eclipse
lasts for a few hours, whereas a total solar eclipse lasts for only
a few minutes at any given place, due to the smaller size of the
moon's shadow. Also unlike solar eclipses, lunar eclipses are safe
to view without any eye protection or special precautions, as they
are no brighter (indeed dimmer) than the full moon itself.
As seen by an observer on Earth on the imaginary celestial sphere,
the Moon crosses the ecliptic every orbit at positions called nodes
twice every month. When the full moon occurs in the same position at
the node, a lunar eclipse can occur. These two nodes allow two to
five eclipses per year, parted by approximately six months. (Note:
Not drawn to scale. The Sun is much larger and farther away than the
Phases of the Moon
Phases of the Moon ( They are Partial
and Total Eclipses)
Understanding The Moon Phases
Have you ever wondered what causes the moon phases? We all know that
its appearance changes over time. But why? The good way to
understand the phases of the moon is to examine an earth-moon-sun
The illustration may look a little complex at first,
but it's easy to explain.
Sunlight is shown coming in from the right. The earth, of course, is
at the center of the diagram. The moon is shown at 8 key stages
during its revolution around the earth. The moon phase name is shown
alongside the image. The dotted line from the earth to the moon
represents your line of sight when looking at the moon. To help you
visualize how the moon would appear at that point in the cycle, you
can look at the larger moon image. This means for the waning
gibbous, third quarter, and waning crescent phases you have to
mentally turn yourself upside down. When you do this, you'll "see"
that the illuminated portion is on your left, just as you see in the
One important thing to notice is that exactly one half of the moon
is always illuminated by the sun. Of course that is perfectly
logical, but you need to visualize it in order to understand the
phases. At certain times we see both the sunlit portion and the
shadowed portion -- and that creates the various moon phase shapes
we are all familiar with. Also note that the shadowed part of the
moon is invisible to the naked eye; in the diagram above, it is only
shown for clarification purposes.
So the basic explanation is that the lunar phases are created by
changing angles (relative positions) of the earth, the moon and the
sun, as the moon orbits the earth.
Partial solar eclipse on May 20,
A Total eclipse in the umbra.
B Annular eclipse in the antumbra.
C Partial eclipse in the penumbra
As seen from the Earth, a Solar eclipse
occurs when the Moon passes between the Sun and the Earth, and the
Moon fully or partially blocks the Sun. This can happen only during
a new moon, when the Sun and the Moon are in conjunction as seen
from Earth. In a total eclipse, the disk of the Sun is fully
obscured by the Moon. In partial and annular eclipses only part of
the Sun is obscured.
If the Moon were in a circular orbit close enough to the Earth and
in the same orbital plane, there would be total solar eclipses every
single month. However, the Moon's orbit is angled at more than 5
degrees to the earth's orbit around the sun (see ecliptic) so its
shadow at new moon often misses the Earth. The Earth's orbit is
called the ecliptic plane as the Moon's orbit must cross this plane
in order for an eclipse (both solar as well as lunar) to occur. In
addition, the Moon's actual orbit is elliptical, often taking it far
enough away from the Earth so that its apparent size is not large
enough to block the Sun totally. The orbital planes cross each year
at a line of nodes resulting in at least two, and up to five, solar
eclipses occurring each year; no more than two of which can be total
eclipses. Total solar eclipses are nevertheless rare at any
particular location because totality exists only along a narrow path
on the Earth's surface traced by the Moon's shadow or umbra.
An eclipse is a natural phenomenon. Nevertheless, in some ancient
and modern cultures, solar eclipses have been attributed to
supernatural causes or regarded as bad omens. A total solar eclipse
can be frightening to people who are unaware of their astronomical
explanation, as the Sun seems to disappear during the day and the
sky darkens in a matter of minutes.
As it is dangerous to look directly at the Sun, observers should use
special eye protection or indirect viewing techniques. People
referred to as eclipse chasers or umbraphiles will travel to remote
locations to observe or witness predicted central solar eclipses…..