Can I really see an eclipse of the Sun?
N.D. Hari Dass and Kamal Lodaya

What is an eclipse?
An eclipse stands for blocking of light. In a cinema, when a person blocks light from the projector, he "eclipses" the screen and the film being shown on it. The Earth eclipses the Moon in the same way in a lunar eclipse.
With a coin, you can block the Sun's light from falling on your eye. For your eyes, the Sun is "eclipsed." The Moon eclipses the Sun like this to show us a solar eclipse.

Are eclipses related to phases of the Moon?
No. Phases of the Moon are a view of the sunlit portion of the Moon, seen from different angles as the Moon goes around the Earth. The picture shows how.
But eclipses require that the Sun, Moon and Earth be in a straight line (so that the shadow of one can fall on the other). Hence they can only happen on New Moon (amavasya) or Full Moon (poornima). Since December 26, 2019, is an amavasya, the Moon can come between the Sun and the Earth on that day. Its shadow falls on the Earth, giving us a solar eclipse.

Why don't eclipses happen every New and Full Moon?
The plane of the Moon's path around the Earth is tilted at an angle of 5 degrees to that of the Earth's path around the Sun, as shown in the figure. So on most New and Full Moons, the Sun, Earth and Moon are not in a straight line.

What are partial, annular and total eclipses?
Because the Moon's path is at an angle, only part of it may fall in the Earth's shadow. This gives rise to a partial lunar eclipse.
For a solar eclipse to be partial, there is an additional reason. The Moon's shadow on Earth is very small. So a central solar eclipse will be partial when seen from most places, and central on a narrow path.
Eclipses are classified as: 
. Partial when the Moon only partially obstructs the Sun, and 
. Central when the Moon maximally obstructs the Sun,
	. Total when the Moon completely obstructs the Sun, and
	. Annular when a thin ring of the Sun's disc is not covered by the Moon.

Why do we have an annular eclipse?
Due to the variation in the Earth--Moon distance, the angular diameter of the Moon and the Sun need not match exactly during a central solar eclipse. Because of this, when the Moon is farther enough from the Earth we get an annular eclipse. When the Moon is close enough to the Earth we get a total eclipse.

What will happen in the December eclipse?
The next central solar eclipse visible from India will be on the day after Christmas, 26 December 2019. All of India will see at least a partial eclipse. Less than half the solar surface will be covered in Kolkata, about three quarters in Hyderabad and 85% in Chennai. Partial eclipse will begin after 8 am and last beyond 11 am. Maximum eclipse will be between 9:24 am and 9:34 am for South India. The figure shows, on both sides of the annularity path, obscuration belts of 90%, 75% and 50%.
Annularity will occur in India between 9:24 am to 9:34 am. The path of annularity will stretch from Mangalore at 13 degrees north latitude, through Kasaragod, Kannur, Kalpetta and Palakkad in Kerala, Madikere and Gundlupete in Karnataka, Ootacamund, Coimbatore, Tiruppur, Palani, Pollachi, Erode, Tiruchi, Karur, Dindigul, Pudukkottai and Karaikkudi in Tamil Nadu at 9 degrees north latitude, before moving on to Sri Lanka. The northern parts of Madurai city and Rameswaram island will have annularity for half a minute.

What is there to see during an eclipse?
It is interesting to monitor the progress of the eclipse itself. Another interesting phenomenon to observe during partial phase is the "Pin-hole" camera effect created by the leaves of trees as sunlight filters through them (more precisely, through gaps in them). Before the eclipse begins, the ground is covered by overlapping discs which are actually the images of the sun. As the eclipse progresses, these discs take the shape of the eclipsed sun. When the eclipse is quite advanced, one sees a myriad collection of crescents! The effect may be enhanced by spreading a white sheet on the ground.
Partial phases can also be observed by projecting the image of the Sun using the pin-hole idea. The following simple arrangement should work quite well: cover a plane mirror with a piece of paper having a circular hole of diameter 1 to 2 cms. The sunlight reflected from this arrangement may be thrown on to a shaded wall indoors. Reduction in the diameter of the hole in the paper will increase the sharpness of the image at the loss of its brightness.

Can I directly see the Sun during an eclipse?
Looking at the Sun, either directly or through the view-finder on your camera, can burn your eyes and cause blindness. Never look at the sun without adequate protection. This will also increase eye comfort by reducing the intensity of sun's visible rays.
The intensity of sunlight for direct safe viewing should be reduced by at least 100,000 times and ultra-violet and infra-red part of the solar radiation should be effectively cut off. Therefore always use a filter that will absorb equally and sufficiently the ultra-violet, infra-red and visible energy of the Sun.
There have been erroneous recommendations suggesting the use of materials that absorb the visible energy but do not absorb the dangerous, invisible infra-red rays.

These filters are NOT safe:
Smoked Glass, Crossed-Polarising elements, Colour film, Sunglasses.

These filters ARE safe:
Dark arc-welders glass, Two or three thicknesses of BLACK and WHITE (NOT colour) photographic film completely exposed and developed.
Place the filter in FRONT of your eyes before facing the sun.

Is this dangerous radiation more during an eclipse?
No. Protecting your eyes adequately means reducing exposure to ultra-violet and infra-red radiation, which is always coming from the Sun. But when you cut off visible light with a filter, you can see that it is not coming through. Since UV and IR radiation is invisible, if your filter does not cut it off, you can damage your eyes without your immediately being aware of it. 
Can I photograph the eclipse with my camera? Since one should NEVER look at the Sun through a camera finder without suitable filters, it is best to aim the camera without using its finder. Filters cannot be rigidly mounted on to mobile cameras, at least not very easily.
One way is to stick suitable filters to cover the camera openings with the help of scotch tapes. It is not advisable to simply hold goggles over the camera openings. Even after fixing filters over camera openings, the danger is that one may inadvertently look up at the sun directly, which should be avoided at all costs.
Another ingenious idea is to have the Sun behind you so the danger of even accidentally looking at the Sun directly does not arise. Most mobile phones come with front facing and back facing cameras. Choose the camera that faces your face and scenes behind your back.Now cover that camera opening with a layer of suitable filter. Now you can look at the screen of the camera without looking directly at the Sun.