Observations
of a Solar Eclipse
Stages of a solar eclipse
The observation
of a solar eclipse can be described according to the different stages that
occur during a solar eclipse. These stages are precise moments of key events
during a solar eclipse, referred to as contacts, which are specified by number,
namely: first, second, third and fourth.
(Click on the links for details on the
features)
First Contact
A solar eclipse
officially gets underway at first contact. The moon begins its passage across
the face of the sun and a small “bite” gradually appears on the edge of the Sun.
This is the point where the partial phases of the eclipse starts and a partial eclipse can be observed. Click here to look at images of sun crescent formed beneath a tree.
A partial eclipse of the Sun
For the next hour and a half, the Moon covers more and more of the Sun’s disk. The sky becomes grayer and darker as this happens(Refer to diminishing light). Shortly before the second contact of the total eclipse, when a small slender crescent of the Sun remains in the sky, wavy lines of alternating light and dark can be seen moving and undulating in parallel on plain light-coloured surfaces. These irregular bands of shadow are called shadow bands.
Around the same
time, an onrushing shadow may appear towards the West. The sky turns deep blue and
the horizon appears to resemble a sunset with a mixture of yellow, indigo and
grey colours.
The moon’s shadow retreats in the distance
Before Totality…
Minutes before
totality, subtle changes do take place in the environment as well as the abnormal
behaviours of wildlife. For example, some animals exhibit changes in eating habits or
settle into roosting earlier than usual. The surroundings hold still and quiet
for a brief moment of daytime darkness. This same situation will continue in
the moments of the darkness of totality too.
As the opposing
horns of the narrow crescent Sun start to converge on one another and the
crescent begins to disappear, tiny specks of light remain visible for a few more
seconds. These points of light are spaced irregularly around the disappearing
edge of the Sun, forming the appearance of a string of beads around the dark
disk of the Moon. They are known as Baily's
Beads. Baily’s
beads make their brief appearance up to 15 seconds before totality. These Baily
beads quickly succumb to the encroaching moon, winking out one or two at a time
until totality is fufilled. The disappearance of the last bead marks the
beginning of the Second Contact.
Baily’s Beads
By now, the
Baily’s beads flicker off one by one till a solitary point of sunlight remains,
shining out from around the rim of the moon as a brilliant burning flare. This
is the “diamond ring” effect that lasts for only a few
seconds. The disappearance of the
diamond ring comes with the vanishing of the last ray of sunlight and totality
begins.
The “Diamond ring” effect
Second Contact
Totality
During totality,
the sky is dark, though not as dark as the usual night. Unusual shadow effects
and shades of colours resulting from scattered light may appear in the horizon.
For a few seconds after the onset of totality, the Sun’s lower atmosphere,
known as the chromosphere, may be observed as a reddish glow around
the edge of the moon.
Chromosphere
Solar prominences can also be seen
around the limb of the moon.
Solar prominence
As totality
arrives, a pearly white crown of light glowing around the darkened solar disk
blazes into view. This is the solar corona (extended outer atmosphere of the Sun).
The full glory of the corona can only be seen during a total solar eclipse.
Coronal light reaches out as far as several diameters of the Sun in the form of
wispy plumes and streamers before they fade into the darkness.
Solar corona,
February 1998, Composite of 12 images.
Around this
time, some brighter stars, planets
or a small comet may be seen near the Sun.
An eclipse presents an opportunity to observe planets in unfamiliar
positions: for example, Mercury and Venus may be admired high up in the sky.
Brighter, irregular or eruptive stars can be observed as well. Brighter satellites or meteors can possibly be seen too.
Observations may be made with the naked eye. If you are lucky you may even
witness features such as zodiacal light or Gegenschein.
A brighter star seen near the Sun
At this point in time, abnormal
wildlife behaviour is apparent. Meteorological observations can also be made. The
period of totality ends as the moon starts to uncover the surface of the Sun.
This is the point of the Third Contact.
Third Contact
The moon’s shadow passes and the first
brilliant spot of sunlight comes into view, breaking the corona and resembling
the “diamond ring” that appeared just before totality. The end of the total
eclipse offsets a reverse of what happened before totality. Similar events
proceeding totality now take place in reverse order on the opposite side of the
Sun. Baily’s beads reappear, followed by the presence of a thin sun crescent
that gradually increases in size as the moon slowly uncovers the Sun. On the
ground, shadow bands may be observed once again. Partial eclipse takes place
once more. With the increasing daylight comes with the awakening and movement
of wildlife and Nature again.
Fourth Contact
Stages of the
partial eclipse take place till the full round disk of the Sun has returned and
normal daylight returns. The moon passes and the shadow on the Sun disappears
at the moment of the Fourth Contact.
Click here to watch webcast of
the Zambia Eclipse 2001
Supplied by http://www.exploratorium.edu/eclipse/zambia/index.html
For a java applet on the Total Eclipse of 1999 August 11 in Europe go to the following link:
This multiple exposure sequence of the 2002
Total Solar Eclipse was taken from near
By