Solar Eclipse Spectacle on Sunday
By Dr N T Jiwaji
REVISED TIMES OF ECLIPSE:
Eclipse STARTS: - 4:24 PM EVENING
MAXIMUM Eclipse, 70%: - 5:28 PM
ENDS WITH SUNSET
On November 3 this year, from 4:24 pm on Sunday afternoon until sunset, we will be among the fortunate few to see a major celestial event that has amazed people since ancient times. In a few countries in Central Africa, within a narrow path beginning in the Pacific Ocean, passing through Gabon, Zaire, northern Uganda, northern Kenya near lake Turkana, Ethiopia and ending in Somalia, people there will be even more lucky. They will witness the Sun being completely covered up, and day will turn to night for them, at least for a short time. In Tanzania we will see about 70 percent of the Sun being covered up, producing a solar crescent when viewed through eclipse glasses.
This November 3 eclipse is a special type of eclipse, called a Hybrid Eclipse, because it starts as an Annular eclipse where a small outer edge of the Sun remains uncovered hence appears as a ring (annulus), and it then turns into a total solar eclipse. Such eclipses are very rare the next such mixed type of Hybrid eclipse will occur in 2023, April 20th over South East Asia
We in Tanzania and in fact over almost the whole of the African continent (see Africa diagram), people will see a partial solar eclipse. Hence this is a major African event and the public is being sensitized to view this amazing spectacle of nature and create wonder in children and youths to drive an interest in Science.
How do eclipses occur? In English language, eclipse is an action word which means “to cover up”. In nature this is exactly what happens during an eclipse. During Solar Eclipses, the Moon covers the Sun and the Moon's shadow falls on Earth (see the solar eclipse geometry diagram).
During Lunar Eclipses there is also a covering up of the Sun, but this time the Earth blocks sun so that its shadow fall on the Moon. While orbiting the Earth, the Moon can line up in such a way that it is between the Sun and the Earth, causing solar eclipses. At other times the Moon can line up in such a way that the Earth is between the Sun and the Moon, causing lunar eclipses.
One may ask that since the moon revolves around the earth every month, we should expect to see one lunar and one solar eclipse each month. Why does this not occur? The Earth moves around the Sun and the Moon moves around the Earth in orbits that are in an exactly flat plane. The orbits are actually slightly inclined to each other hence the Moon misses blocking the Sun most of the time. Eclipses only occur when the Moon is exactly where the inclined orbits cross each other. This happens only about three or four times in a year. The result is that we usually have about two to four eclipses in one year.
Another reason why eclipses occur is because of the size of the Moon and the Sun are exactly the same as viewed from Earth. When viewing the Sun through protective glasses we realize that it looks exactly the same size of a Full Moon. Though the Moon’s diameter is very small (3,500 km) and the Sun’s diameter is 400 times bigger (1.4 million km), they look the same size to us because the Sun is also 400 times farther away from us than the Moon. Hence their apparent sizes look exactly the same from Earth. This is in fact an amazing coincidence of nature; hence the rarity of eclipses is even more appealing to the public.
It is easy to demonstrate that a very small object can cover up your view of a very large object. Cut out a small circle from a cardboard and hold it a short distance from your eyes. You will see that it can hide even a whole building or a tree, as shown in the diagram.
It is also interesting to note that Solar eclipses only occur at New Moon. At this time the Sun is behind the Moon whose dark side is faces us. During a solar eclipse, the dark face of the Moon comes exactly in front of the Sun hiding the Sun from our view. On the other hand, lunar eclipses only occur at Full Moon, as happened during the recent Penumbral Lunar Eclipse from midnight of October 19. During a Full Moon, the Moon’s face is fully lit by the Sun which is below us, on the daytime side of the earth. You can imagine the Earth (i.e. we) being between the Sun and the Moon, so the Earth’s shadow can fall on the Moon, causing a Lunar eclipse. These two types of eclipses often follow each other as it happened this time when two weeks after the October 19 Lunar eclipse, we are getting ready for the November 3 Solar eclipse.
We have mentioned several types of solar eclipses: Total, Partial, Annular and Hybrid solar eclipses. These different types of eclipses occur depending on which type of Moon's shadow reaches us on Earth. When you are in the dark shadow region (called umbra) then you will see a total eclipse where all sunlight will be cut off when the whole of the Sun's disk is covered by the disk of the Moon. This is of course one of the most amazing views in nature, because day suddenly turns into night, at least for a short time. This is the only time that one can view the Sun's outer atmosphere called the corona and that itself is an amazing sight worth experiencing. It is much cheaper and many more scientists can use the opportunity of a Total Solar Eclipse to study the Sun and its corona and its interaction with the Earth's atmosphere.
An Annular Eclipse (or ring type) occurs when the Moon's shadow is in a mixed region where the dark umbra does not reach the surface of the Earth. In real terms what happens is that the Moon is just slightly more distant from Earth and so its apparent diameter is just smaller than that of the apparent diameter of the Sun. Hence the outer edge of the Sun is not covered by the Moon's disk and an annulus or a ring of sunlight is seen from Earth. Tanzania will be the center of world's attention on September 1, 2016 when an Annular Solar Eclipse will pass through central Africa centered over Southern Tanzania. It will be a major experience for everyone in Tanzania and we have to prepare to many eclipse viewers from within Tanzania as well as international eclipse chasers to come to Tanzania.
The eclipse the we will see on Sunday November 3 will be a partial eclipse. Part of the Sun will be covered up by the Moon's disk while the rest of the Sun will be in faint shadow (penumbra). Make sure that you have correct viewing glasses. If you do not have eclipse glasses, welder's glass number 14 can be used. The best thing is never to look at the Sun continuously. The Sun gives off extremely powerful energy SO NEVER LOOK AT THE SUN DIRECTLY OR THROUGH A TELESCOPE - YOU WILL BE BLINDED INSTANTLY.
Starting from 4:24 pm in the afternoon, using safe eclipse viewing method, you will see the western edge of the Sun begin to be covered up by the Moon's disk. This will progress slowly until 5:28 pm when the maximum amount of the Sun's disk will be covered up. In northern Tanzania, more than 80 percent of the Sun will be covered up at maximum eclipse while for people in southern Tanzania, 60 percent will be covered up. In Dar es Salaam we expect more than two thirds of the Sun will be covered at maximum eclipse around 5:30 pm. At this time, the Sun will appear as a crescent when viewed though safe glasses.
After the maximum eclipse around 5:30 pm, the crescent of the Sun will increase in size until the last of the dark edge will clear just after sunset, so we will not see that last bit. The changes is the Sun occur slowly over a period of more than 3 hours so there is no need to watch the eclipse continuously and you can easily share a pair of eclipse glasses between several people.
Besides eclipse glasses and welder glass number 14 you can watch the progress of a solar eclipse using the projection method. You will have noticed that when sunlight comes through any small hole in a large piece of cardboard, you see a circle of light illuminated within the shadow of the cardboard. The circle is actually the image of the Sun, and this method is called the pin hole method of viewing. So when the Sun is partially eclipsed, you will see a crescent shape instead of a circle. You can easily follow the progress of the eclipse using this method of projection. Even light passing through gaps between the leaves of trees will show many crescents on the ground.
Prepare yourself for this unique opportunity to see our amazing universe at work producing remarkable spectacles like this Sunday's Solar eclipse. For further information and latest details visit this website:
MAKE SURE YOU PROTECT YOUR EYES WHEN WATCHING THE SUN.