Solar
eclipses
There are two types of eclipses observed from Earth; solar and lunar.
Both require the direct alignment of the Earth, Sun and Moon in space.
They can be both spectacular and even quite chilling to observe and
have been the subject of worship and study since mankind looked to the
heavens for inspiration and knowledge.
The most spectacular and awe inspiring type of eclipse is the solar
eclipse, which occurs when the Moon passes between the Earth and the
Sun, blocking the disc of the Sun.
Solar eclipse
The occurrence of solar eclipses has been well documented,
measured and even predicted since ancient times. Stonehenge is thought
to have been used, among other astronomical observatories, as a calculator
for solar eclipses.
Solar
eclipses occur fairly regularly, at least twice per year. Because they
only last for quite short periods of time, however, it's only possible
to observe an eclipse from specific places on the Earth's surface on
each occasion. A solar eclipse can not be observed from all parts of
the Earth at the one time.
A solar eclipse will always occur at New Moon, when the Moon passes
closest to a line directly between the Sun and Earth. Although all solar
eclipses occur at New Moon, each New Moon does not herald a solar eclipse.
This is because the orbit of the Moon around the Earth is slightly out
of alignment with that of the orbit of the Earth around the Sun. It
is only when the orbit of the Earth and Moon coincide with a direct
line to the Sun that a solar eclipse occurs.
Total eclipse
Total solar eclipses are times of great astronomical activity,
not only to observe this awe inspiring event, but also to study the
outer atmosphere (the corona) of the Sun. It happens that the disc of
the Moon is usually just the right size in the sky to black out only
the disc of the Sun, thus leaving the outer atmosphere in full view.
As the shadow of the Moon moves over the observer and the sky darkens,
totality occurs for a few minutes and stars and planets can be seen
that are normally invisible to us by day.
Annular
eclipse
Sometimes the Moon is a little further away from the Earth than
average when it passes in front of the Sun. In this case, it does not
obscure the whole of the Sun's disc, but instead leaves a ring of light
around the outer edges of the Moon as it passes in front of the Sun.
This type of less spectacular eclipse is known as an "annular eclipse".
Partial eclipse
A total or annular solar eclipse can be seen only from a narrow path
across the Earth's surface, which is, at most, a few hundred kilometres
wide. Much more common are partial eclipses of the Sun, in which only
part of the Sun is obscured. From any given location, such an event
occurs once every few years. As not all of the Sun's disc is covered
by the Moon, it does not get dark. Anyone not knowing a partial eclipse
is in progress would not normally notice the slight change in light
intensity.
Solar eclipse events
Three main effects can be seen during a total eclipse of the Sun :
As the edge of the Moon almost obscures the disc of the Sun, a bright
concentration of light becomes visible along its edge. This is the "Diamond
Ring" effect; the diamond is simply the last part of the Sun still
visible before it too is covered.
As soon as the Sun's disc is darkened, a bright halo can be seen.
This is the Sun's corona, or atmosphere. The corona is normally not
visible next to the bright solar disc. Spectacular solar prominences
can also be seen leaping through the corona millions of kilometres into
space.
Finally,
as the Moon moves away and the edge of the Sun again becomes visible,
a second diamond ring occurs. Just before and after totality, smaller
"diamonds" can also be seen around the edge. Known as "Baily's
Beads", these occur as the rough surface of the moon's edge breaks
up the incoming light.
Observing solar eclipses
Direct viewing of a solar eclipse is not safe. Looking directly at the
Sun, whether by naked eye, through a telescope, binoculars, sunglasses
or tinted glass can cause permanent damage to the eye.
The old adage - "Never look directly at the Sun " is true
at all times!
The only safe way to observe a solar eclipse is by focussing a telescope
onto a white card placed some distance from the telescope, so as not
to burn the card.
View the card with your back to the Sun. You will be able to see the
disc of the Moon pass as a silhouette over the Sun on the card.
Caution
-Do not look through the telescope to focus the Sun on the card!
Performed correctly, this method of observation is quite safe. If you
have not carried out this procedure before, please consult an astronomer
or experienced science teacher before trying this yourself.
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