Unique Solar Eclipse for 2010

By Dr Noorali Jiwaji

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(Two diagrams attached)

(Welder's glass recommended for observations)

While promoting the Astronomy throughout 2009 during the International Year of Astronomy and even this year we in Tanzania have not been too lucky with eclipses.  Such events are the most eye-catching and attract many people to take an interest in the worlds above and beyond ours.

The only eclipse that was visible to us in Tanzania during the whole of the last year 2009 was the one that occurred in the dying hours of the year and ushered in the New Year. We received it as a year-end parting gift.

This year too, the only eclipse that we are in a position to see is the solar eclipse that will occur on the morning of Friday 15^th January 2009.  Of the four eclipses that will occur this year, this is the only one that we will be able to enjoy fully.  We will take it to be our signal for all the other delights that astronomy will be offering during the rest of this year. This eclipse will also be seen by observers in East Africa, southern India, Sri Lanka and China.

This Friday’s partial solar eclipse will occur between 7:08 am and 11:17 am, with maximum eclipse at 8:32 am.  While people are on their way to work, students on their way to school and all beginning their day’s activities the Sun will surprise us with a dramatic decrease in brightness.

At 7:08 in the morning, the Sun’s disk will begin to be covered from the top edge while you watch the Sun from the East.  However it is not possible to watch the Sun directly.  This is something that you must already have noted, since just a passing glance at the burning bright Sun will blind you for several seconds or minutes and you will see dark spots in your vision that will only go away after many more minutes.  Your eyes will just not allow you to look at the Sun for even a fraction of a second because it is a very painful experience.

The only way to observe a solar eclipse directly is through dark glass such as a welder’s glass use to look at objects in the bright light of arc welding. Such pieces of glass are sold in most hardware stores, in small pieces, for around one or two thousand shillings each.

If you do not have that, then you can project the image of the Sun on a tray filled with water and you can watch the reflection of the Sun in the water.  Partial solar eclipses can also be noticed in the shadows cast by small objects such as leaves in a tree.  The bright parts will have crescent shape when the Sun is partially eclipsed.

Our eyes are often fooled by the decrease in brightness of the Sun, especially during total eclipses since it becomes more comfortable for our eyes. But dangerous rays continue to enter the eyes and can still damage the eyes.

SO NEVER LOOK AT THE SUN DIRECTLY WITHOUT HAVING ANY PROTECTION.

Lunar eclipses on the other hand are completely safe to see since we are only looking at the reflected light from the Moon.  We watch the Moon regularly in the night sky so during a lunar eclipse the light is reduced even further.

Having secured protection for your eyes, go out and look through it at the Sun at 7:10 am. You will see a slight arc eaten away from the Sun from above, as shown in the first picture.

Eclipse means “covering up”. So what is happening is that the Moon, as it orbits us, comes between us and the Sun as shown in the eclipse geometry diagram.  As the eclipse progresses, more and more of the Moon’s disk will cover up the top part and a crescent will be seen at the bottom (see diagram for 8:00 am).

By half past eight at 8:32 am the maximum amount of about 80 % the Sun’s disk will be covered up.  Through the protective glasses the Sun will be seen as a thin crescent shape on the right.  Observers in the north will see the Sun covered up more than 80% while those in the south will see less amount covered up.

The crescent will then increase as the Moon’s disk slides slowly away from the Sun from bottom (see diagram for 9:00 am). By 10:10 am only a small part of the Sun’s edge will be eaten away by the Moon and the eclipse will finally end at 17:17 am and the Sun will finally be free of any obstructions of its magnificent fiery face.

One damper that can come in our way is the weather.  All the five-day forecasts that I have followed are predicting scattered thunderstorms or light rain.  I do hope that this means that we will, at the very least, be able to have a peek at the Sun through the clouds once in a while as the eclipse progresses.  So be prepared to take the opportunity whenever the clouds break.  Even with the Sun in the clouds you can expect to see a significant decrease in daylight by 8:30 am when the eclipse is at maximum.

So why do eclipses occur?  The Earth moves around the Sun and the Moon moves around the Earth.  Since all these orbits are in one flat plane, once in a while the Moon will be in a position between the Sun and Earth and will block our view of the Sun, causing an eclipse. You may ask that the Moon should block the Sun during each orbit causing eclipses every month.  But we know that this does not happen, which means that the orbits are very slightly inclined to each other hence, most often, the Moon misses blocking the Sun.  Eclipses only occur when the Moon is exactly in the position where the inclined orbits cross each other.

Another reason why eclipses occur is because of the size of the Moon and the Sun.  When viewed from Earth, both the Moon and the Sun look exactly the same size.  When viewing the Sun through protective glasses you will realize that looks exactly the same size that the Full Moon looks at night.  Though the Moon has very small (diameter 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 the same from Earth.  This is in fact a complete coincidence in nature; hence the rarity of eclipses is even more appealing.

Our neighbours in Kenya and Uganda will see an even more unique event.  Along a narrow path just North of Tanzania, the Moon will cover the Sun just enough to leave a shining ring around it.  This is called an Annual Eclipse (annulus is ring in Latin).  Such an eclipse occurs because the Moon is just a little bit farther away from us and hence its apparent size is smaller than that of the Sun.  The orbits of our planets and Moon are not perfect circles but they are very slightly elliptical hence sometimes the Moon is farther from us and sometimes nearer.

Solar eclipses occur at New Moon since immediately after, that the Moon, as it begins its lunar cycle, shows its first crescent in the west just after sunset.  On the other hand, Lunar eclipses occur on Full Moon days since the Moon’s face is fully lit by the Sun which is on the other side from where we are on Earth and the Earth’s shadow falls on the Moon causing a Lunar eclipse.

The eclipse that we will see on Friday is follow on from the one we saw on New Year’s Eve, which was a lunar eclipse. This means that both have happened during that same orbit of the Moon.  This happens often since the conditions will still just be right for an eclipse to occur during the few days from Full Moon to New Moon.

Let us keep our fingers crossed so that the weather cooperates to allow us to see and experience this unique event of the year.

END