Solar Eclipse of 15th January 2010

First Solar Eclipse of 2010 – A Unique Experience

By Dr Noorali Jiwaji

While the whole of the last year 2009 passed without an eclipse seen in Tanzania, the lunar eclipse that occurred in the dying hours of the on New Year’s Eve saved the day. Immediately thereafter, two weeks later, on the morning of Friday 15^th January 2010 we witnessed a much more dramatic solar eclipse. Eclipses catch people’s imagination. They cause excitement for some and stir up concern for others so these were unique events indeed.

The two eclipses are even more unique because though eclipses occur regularly, we in Tanzania will have to wait more than a year and a half to see the next total lunar eclipse on June15, 2011 and even longer, nearly four years, for the next partial solar eclipse of November 3, 2013.

Friday 15^th January’s partial solar eclipse began at 7:08 am and ended at 11:17 am, and maximum eclipse was observed at 8:32 am. The previous days were cloudy and with thunderstorms so there was concern whether we would be able to even see the eclipse. However, nature, as ever, smiled on us and though there were clouds, we were able to see the full glory of the eclipse.

When I went up to the terrace of my house at 7 o’clock in the morning, I could not see the sun due to thick clouds. But 10 minutes later when lighter clouds were over it, I immediately noticed that a slight arc was cut off from the top of the sun. I was surprised that I could watch the sun with my naked eyes, but that was because the clouds were not so thick and had reduced the sun’s intensity sufficiently. It felt like I was watching the moon; since in my view, the sun was exactly the same size as that of the moon that I normally see at night! In fact this is the reason why eclipses occur - as viewed from earth, the size of the moon is just right to be able to just cover up the whole sun.

IT IS STRONGLY ADVISED THAT YOU SHOULD NEVER SEE THE DIRECT SUN WITH YOUR NAKED EYES. I was prepared to view the sun using several different methods. I had a welder’s glass with me, together with a bucket of water to see the sun’s reflection. I also intended to see the eclipse by projecting it from a telescope. It is also possible to see the sun as an image projected through a pin hole but I had not prepared that in advance.

While I was watching the sun through the clouds, the clouds moved off and the sun was fully exposed. Because of its blinding brightness I had to avert my eyes immediately. But I could see a bright spot in my vision that remained for a several seconds. This usually happens when you look at a blindingly bright light. I was amazed that though the ghostly bright spot was a circle, part of it was sliced off! I had seen a ghost eclipse!!

By 8 am, though the sun was still shining clearly, I was able to watch it through welder’s glass. A significant part of the sun was now covered up by the Moon. The sun was still quite bright, even through the glass, so I did not watch the sun continuously. Only through very dark welder’s glass (rated at No. 14) can you see the sun comfortably cool.

By the time of maximum eclipse at 8:32 am, the moon had covered up nearly 80% of the sun’s disk. The moon had overlapped the sun almost fully and the sun was seen as a crescent. This was a unique situation because we regularly talk about a crescent moon and here I was watching crescent sun!

When I next tried to look at the eclipsed sun in a reflection off the surface of the water in the bucket, the sun was too bright and not at all comfortable to the eyes. The morning sun was too low, so most of the sunlight was reflected off the surface to the water. Only when the sun is overhead can you watch the sun’s reflection comfortably since only 6% of the light would be reflected from the water surface.

The remaining trail was to project the sun’s image through a telescope onto a piece of paper. It was rather difficult to align the telescope towards the direction of the sun since it is not possible to look at the sun directly. So it was aligned using the shadow of the telescope. When the telescope points in the direction of the sun, it is well aligned with sun. With further minor adjustment it was possible to get the bright circle of light from the telescope eyepiece to fall on to a piece of paper. The bright circle of the sun, projected on the piece of paper, was cut off from one side where the eclipsed sun was covered by the moon.

How do eclipses occur? Eclipse means “covering up”. As the moon orbits the earth, it comes between the earth and the sun. As we watch the sun at this time, the moon’s disk slowly starts to overlap the sun from one edge. As the eclipse progresses, more and more of the sun is covered up until maximum. As the moon slowly shifts further, more and more of the eclipsed sun gets exposed until finally the whole sun is visible again and the eclipse is over.

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 occur only when the Moon is exactly in the position where the inclined orbits cross each other which is only about three or four times in a 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 a complete coincidence in nature; hence the rarity of eclipses is even more appealing.

Solar eclipses occur at New Moon since the next evening the moon is seen as a thin crescent in the west just after sunset. On the other hand, lunar eclipses occur at Full Moon since the moon’s face is fully lit by the Sun which is on the daytime side and the Earth’s shadow falls on the Moon causing a Lunar eclipse. Hence these two types of eclipses often follow each other as it happened this time with a lunar eclipse on New Year’s Eve and the solar eclipse two weeks later.

I was happy that I was able to appreciate sights offered by nature, and understand it, and to have been able to view the solar eclipse using three of the five ways.

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Email: ntjiwaji at yahoo dot com