A solar eclipse occurs when the moon gets between Earth and the sun, and the moon casts a shadow over Earth. A solar eclipse can only take place at the phase of new moon, when the moon passes directly between the sun and Earth and its shadows fall upon Earth’s surface. But whether the alignment produces a total solar eclipse, a partial solar eclipse or an annular solar eclipse depends on several factors. There will be a time that there is a last eclipse because the moon is moving away from the earth, ever so slowly. Popular Mechanics wrote a great article on the topic.
Types Of Solar Eclipses
There are four types of solar eclipses: total, annular, partial and hybrid. The breakdown of solar eclipses breakdown is that based on rough estimates:
28 percent are total solar eclipses
35 percent are partial solar eclipses
32 percent annular solar eclipses
5 percent are hybrid solar eclipses
Total solar eclipses
A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solar corona to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of Earth. This narrow track is called the path of totality. Although the length of total solar eclipses vary, totality may last as long as 7 minutes 31 seconds. The average time between total eclipses occurring somewhere on Earth is roughly 18 months.
The umbra is that part of the shadow where all sunlight is blocked out, which takes the shape of a dark, slender cone. The umbra is surrounded by the penumbra, a lighter, funnel-shaped shadow from which sunlight is partially obscured.
Only those in the path of the total solar eclipse can see the corona, which is the outer atmosphere of the sun, during totality. During a total solar eclipse, the moon will cast the umbra upon Earth’s surface, which can sweep a third of the way around the planet in several hours.
Partial Solar Eclipses
A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra passes above the Earth’s polar regions and never intersects the Earth’s surface. Partial eclipses are virtually unnoticeable in terms of the sun’s brightness, as it takes well over 90% coverage to notice any darkening at all. Even at 99%, it would be no darker than civil twilight. Of course, partial eclipses can be observed if one is viewing the sun through a darkening filter.
Annular Solar Eclipses
An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, but in this instance, the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon. One could say that an annular eclipse is somewhat similar to a partial eclipse. The maximum duration for an annular eclipse is 12 minutes 30 seconds.
An annular solar eclipse is similar to a total eclipse in that the moon appears to pass centrally across the sun. The difference is, the moon is too small to cover the disk of the sun completely. During annular solar eclipses, the antumbra, a theoretical continuation of the umbra, reaches the ground, and anyone situated within it can look up past either side of the umbra and see an annulus, or “ring of fire” around the moon.
Hybrid Solar Eclipses
A hybrid eclipse, also called annular/total eclipse, shifts between a total and annular eclipse. At certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. Hybrid eclipses are comparatively rare. An A-T eclipse begins as an annular eclipse because the tip of the umbra falls just short of making contact with Earth. During this process, it becomes total eclipse because the roundness of the planet intercepts the shadow tip near the middle of the path. It ends when it it returns to annular toward the end of the path. Because the moon appears to pass directly in front of the sun, total, annular and hybrid eclipses are also called “central” eclipses to distinguish them from eclipses that are merely partial.
Solar eclipse safety
It is ALWAYS dangerous to look at the sun without proper protection! If using a telescope of camera, make sure to use a proper filter!
Acceptable filters for unaided visual solar observations include aluminized Mylar. Some astronomy dealers carry Mylar filter material specially designed for solar observing. Other acceptable options include 14 arc-welder’s glass, which are available for just a few dollars at welding supply shops. It is always recommended that users test filters and observing techniques before eclipse day to make sure that the user knows how to work them.
Unacceptable filters –These include sunglasses, old color film negatives, black-and-white film that contains no silver, photographic neutral-density filters and polarizing filters. Although these materials have very low visible-light transmittance levels, using these will transmit an unacceptably high level of near-infrared radiation that can cause a thermal retinal burn. Regardless that the sun appears dim, or that there is no discomfort when observing the sun, there is no guarantee that your eyes are safe.
If you’re interested in photographing a solar eclipse, we will be writing an upcoming article written by expert astrophotographer Konstantin. So keep checking in for more information!
Interesting Solar Eclipse Cultural Myths
The earliest written record of a solar eclipse occurring was from over four millennia ago in China, where it was believed that the gradual blotting out of the sun was caused by a dragon who was attempting to devour the sun. Therefore, it was the duty of the court astronomers to shoot arrows, beat drums and raise whatever cacophony they could to frighten the dragon away.
It turns out that the timid emperor Louis of Bavaria, the son of Charlemagne took the term “scared to death” literally, when witnessing an total eclipse of the sun on May 5th 840 A.D. When the sun returned back to view, the emperor Louis became so overwhelmed by the sight that died of fright!
During a total solar eclipse, a few ruby-red spots may seem to hover around the jet-black disk of the moon. Those are solar prominences, tongues of incandescent hydrogen gas rising above the surface of the sun. During the total eclipse of Aug. 18, 1868, the French astronomer Pierre Janssen trained his spectroscope on the prominences and discovered a new chemical element. Two English astronomers, J. Norman Lockyer and Edward Frankland, later named it “helium,” from the Greek helios (the sun). The gas was not identified on Earth until 1895.Advertisement
And because sunlight is blocked during a total eclipse, some of the brighter stars and planets can be observed in the darkened sky. Under such conditions astronomers were able to test part of Einstein’s now-celebrated general theory of relativity. That theory predicted that light from stars beyond the sun would bend from a straight path in a certain way as it passed the sun. The positions of stars photographed near the sun’s edge during a total eclipse on May 29, 1919, were compared with photographs of the same region of the sky taken at night; the results strongly supported Einstein’s theory.
Resources and More Information
NASA Eclipse Website for historical and upcoming data