Types
of Solar Eclipse
There are four
different types of solar eclipse, namely Partial eclipse, Annular eclipse,
Total Eclipse and Hybrid Eclipse.
Partial Eclipse
A partial solar eclipse occurs when only part of the Sun is covered by
the Moon which appears to take a “bite” out of the Sun. This is the general
appearance of a partial eclipse.
Partial eclipses occur when the umbral shadow
of the Moon misses the Earth and only its penumbral shadow falls on the Earth’s
surface. Refer to Figure 1B. In this case, the umbral
shadow will either pass over the north or south poles of the Earth. Note that
the area of the Earth that falls within the area of the penumbra will experience
the partial eclipse.
Figure 1B
Within the penumbral area, the Sun is partly covered and there is dim
light of varying degrees. Observers within the area of the penumbra and close
to the umbra will see the Sun almost covered while observers at the edge of the
penumbra will see a crescent Sun.
A partial eclipse begins occurring with the onset of the First Contact
and the onset of the Third Contact of a total eclipse where it looks like the
crescent Sun as in the picture above. A partial eclipse also always accompanies
a total eclipse, falling over a larger area of the Earth’s surface. This is due
to the penumbra always surrounding the umbra.
Observers outside the path of totality or annularity during a total or
annular eclipse may also experience a partial eclipse.
Partial Solar Eclipse. In courtesy of http://www.hartrao.ac.za/eclipse2002/
Annular Eclipse
An annular(annular comes from the Latin annulus or ring) eclipse occurs when the Sun’s center is
covered by the moon , leaving its edges left uncovered, producing a ring (or
annulus) of the Sun around its edges.
Annular eclipses occur when the moon appears smaller than
the Sun.
1994 eclipse animation courtesy of Fred Espenak
Annular Eclipse
The Moon and its elliptical orbit is
further from the Earth and its umbra is too short to reach the Earth. But the
moon is located exactly in front of the Sun. This enables the umbral area below to observe the centre of the Sun covered,
leaving a ring (an annulus) of the Sun visible around the edges of the moon.
Observers in the penumbral area witness a normal partial eclipse instead.
In an annular eclipse, you don't get to see
any of the "special effects" of a total eclipse, such as the corona,
or diamond ring effect. The thin sliver peeking around the moon is far too
bright to allow this.
Total Eclipse
A total solar eclipse takes place when the Sun becomes
completely covered by the moon.
In a total solar eclipse, the moon, in its elliptical
orbit, passes between the Sun and the Earth at a point where it is also quite
close to the Earth. As this occurs, a shadow is cast upon the Earth’s surface.
The umbral part of the moon’s shadow is the area
where the Sun is completely blocked off by the moon. The moon appears close
enough to the Earth during a total eclipse and observers within the umbra will
witness a total eclipse of the Sun where the Sun’s face is totally blocked off
by the moon.
Total Solar
Eclipses
Hybrid Eclipse
The Hybrid eclipse is a fairly rare event. A hybrid, or
annular or total eclipse, is one which is seen as annular by observers in one
part of the Earth, and at the same time, is seen as a total eclipse by others
in another part of the Earth. The diagrams below show how a hybrid eclipse is
formed.
The moon is merely far enough from the Earth but the umbra
cannot reach the sides of the Earth. As eclipse takes place, the western part of
the Earth will see an annular eclipse. Observers in the outer parts of the
eclipse track (outlined in green) will witness an annular eclipse.
The eclipse is annular when it begins and ends. However, as
a result of the curvature of the Earth’s surface, the apparent size of the moon
increases in size till it is just enough to produce a total eclipse.
As the eclipse path continues to move on, the umbra does
not need to travel far to reach the Earth, and is also just long enough to
reach the center which faces the moon directly. Observers in the outlined blue
area will witness a total eclipse.
The eclipse remains a total eclipse till the end of the
eclipse when it will develop into an annular eclipse again.
Hybrid eclipses always have short duration of the annular
and total eclipse phases.
Deciding
Factors for the type of Solar Eclipse to Occur
The type of eclipse that does occur
depends on several things. First, if the eclipse happens when the sun is further
from the node, it is more likely that the eclipse will be a partial one. In
this type of eclipse, the dark umbra passes above the North Pole or below the
South Pole, never touching the earth. All we ever see is part of the sun
covered.
There's another variable, though. Remember
that the orbits of the earth and moon are not perfect circles, but rather
ellipses. Note that in the diagram above (again wildly out of scale), the earth is sometimes closer to the sun and sometimes
further. The same is true for the moon--sometimes it's closer to the earth and
sometimes it's further. See the table below:
|
|
Close Distance |
Far Distance |
|
Sun |
147,101,455 km |
152,098,155 km |
|
Moon |
356,749 km |
406,282 km |
As you can see, both the sun and the moon
change their distances quite significantly. The moon changes by about 14 per
cent, and we vary our distance to the sun by about 3 per cent. Because of this,
the sun and moon look bigger sometimes and smaller at other times. If we're far
from the sun so that it looks smaller, and close to the moon so it looks
bigger, the moon will be able to cover over the entire face of the sun as seen
from earth, and we'll see a total eclipse. If the opposite is true and we're
close to the sun and far from the moon, the moon will appear too small to cover
the face of the sun, refer to table 1A below.
In this case, it's like trying to cover a
penny with a dime. You would see a ring of copper penny sticking out on all
sides of the dime. This happens with the sun and moon. You see a ring of the
sun shining around the edges of the moon --- annular eclipse.
|
Position of Earth |
Position of Moon |
Type of Solar Eclipse |
|
Aphelion (maximum distance from
Sun) Sun image minimum |
Perigee (minimum distance from
Earth) Moon’s image maximum |
Total |
|
Perihelion (minimum distance from
Sun) Sun’s image maximum |
Apogee (maximum distance from
Earth) Moon’s image minimum |
Annular |
Table 1A. Orbital conditions of
Earth and Moon for solar eclipses.