Tuesday, July 24, 2018


By Dr. Noorali T. Jiwaji
Friday night of 27 July is a night not to be missed for observers of the night sky.  On that night, the Full Moon will be covered up when it passes through the Earth’s dark umbra shadow when the Sun, Earth and Moon align almost exactly along a straight line producing an extremely deep eclipse that will last longest for this whole century.  
The Moon will be covered up for longest time because it will be at its farthest distance from Earth hence it will be in the widest part of Earth’s shadow, almost three Moon diameters wide. This total lunar eclipse will last 1hr43min which is close to two hours. Such long total lunar eclipses are extremely rare since the next longest lunar eclipse of 1hr46min will occur after 107 years on June 09 2123.  
Lunar eclipses can be observed safely with naked eyes because the light from the Moon does not harm us and when it is covered in shadow it is very easy to watch directly.  
The lunar eclipse will start becoming visible at 9:24pm from the eastern edge of the Moon and over the next hour the dark black edge of the shadow will slowly slide westward until it reaches the west edge by 10:30pm when the whole Moon will enter the Earth’s shadow and the whole Moon will turn red.

 For the next two hours the whole Moon will remain completely covered by Earth’s shadow with mid eclipse at 11:21pm and the total part of the eclipse ending at 12:13pm when the east edge of the Moon will begin to come out of the shadow. This partial part of the eclipse will end when the whole Moon will have left Earth’s umbra at 01:19am.  

Though we see only the visible part of the eclipse at the above given times, there is an invisible part that is can be just noticeable if you observe the brightness of the Moon very carefully.  
This phase of the eclipse is called penumbral eclipse when the Moon enters a penumbral thin shadow that surrounds the central umbral dark shadow. For this July 27 eclipse, the penumbral eclipse begins at 8:14pm until 9:24pm when begins the partial visible part.
At the other end, after the end of the partial phase at 01:19pm, the Moon is again fully inside the Earth’s penumbra.  The whole eclipse end with the end of the penumbral phase at 02:28am.

During the total phase of the lunar eclipse, although the whole Moon will come be within the Earth’s shadow, the Moon will not disappear from view because some sunlight that will have been bent by the Earth’s atmosphere will be bent inside the shadow producing a deep red colour of the Moon.  This is a sight not to be missed.
The next such deep eclipse will not occur over Tanzania for the next nine years until September 07, 2025. Only red light remains after being bent by the Earth’s atmosphere so the whole Moon will become a deep red colour ranging from dark deep red to bright orange red with the corresponding Danjon Scale ranging from 0 to 4.  
A clean atmosphere produces a bring orange red colour of scale 4 while a polluted atmosphere produces brownish or grey colour of scale 1 or even very dark almost invisible eclipse at scale 0. So viewing this total lunar eclipse will give you a chance to gauge the state of cleanliness of our atmosphere and even report your Danjon value for scientific use.

The night Friday 27 July is also extremely unique because the Moon will be joined close by with brilliant Mars.  Lunar eclipses occur during Full Moon when the Moon rises in the east at sunset so that it is exactly opposite to the Sun and shines full face on the Moon.  
Planet Mars will also be, by luck, in the same situation and will be exactly opposite the Sun (i.e. Mars will be at opposition). So, on Friday 27 July, the Moon will rise in the east just as the Sun sets in the west.  On the other side, in the east Mars and Moon will rise close from the horizon, close together. This will be a spectacular sight since Mars will be extremely bright with the bright Moon close to it.

Three other planets will also be seen together with Moon and Mars.  The planets are in order, from east to west, Saturn, Jupiter overhead and Venus bright in the west skies.  
They will form an exact line from going from east to west. This line is not by chance; it shows that our Solar System is a flat plane and we are observing the Solar System from inside Earth hence when we look up at the sky we are looking along the plane of our Solar System.  
Through a telescope Saturn is the most spectacular with its wide ring system surrounding the planet, while Jupiter shows its Galilean moons changing positions around the planet like a mini solar system.
Venus, when seen through at telescope, shows up as a half phase. Venus shows changes in phase because its orbit is inside that of Earth so when its night side turns towards us, the bright sunlit side shows changing phases depending on its position in its orbit relative to Earth. Mars, though extremely bright shows up as a brilliant orange dot through at telescope and unfortunately, we cannot see any features on its face at the moment because there is a dust storm that has enveloped the planet.

The night sky also shows a wide path where there are many stars while the rest of the sky has much fewer stars.  People in rural areas will notice this wide path very quickly, crossing from south direction going to the north east direction.  This wide path of stars is called the Milky Way and is actually our Milky Way galaxy. It is seen in a narrow region because our galaxy is also a flat system and we are seeing it from inside the galaxy because we and our Solar System are inside the Milky Way galaxy.  

You can also see in the south direction stars that make up the Southern Cross constellation.  Near it you can make out the Scorpio constellation because of its shape like a scorpion.

Suggestions for teachers and parents
The eclipse will take place on a Friday night until past midnight.  Since the next day is an off day for schools, teachers should encourage their pupils to urge their parents to watch the eclipse progress in all its phases from partial to total eclipse and see the blood red Moon during the total phase of the eclipse.
Teachers can take this opportunity to prepare their pupils and students to watch this Lunar eclipse at home together with their parents and family and friends, and after that to discuss in class what they observed.
The teacher can use the Social Studies book class six where eclipses are described in the Solar System topic. Even for lower classes, teachers can use the relevant text.
Secondary School students can also be prepared to watch this event by reminding them of what they learnt in primary school and connect it with what they learnt in Geography Form One in the Solar System topic that describes Solar and Lunar eclipses.
Form Four students of Physics in the topic of Astronomy will also gain a lot from observing this event and learning about eclipses as an additional topic that is very important and very exciting, although it is not in their syllabus and also not in their book.  This event will also be of interest to all Science students as well as those in Form V and VI as well as Science students in Colleges and Universities.
By any method the teacher will draw the positions of the Sun, Earth and Moon together in a line and show the types of shadows and explain to the students what they will see at night when they observe the Lunar eclipse.
Pupils and Students can write down what they see during the event and answer the following questions:
- Did they see the Moon?
-What was its shape?
-Did they see the red planet Mars?
-Did they see Saturn by distinguishing it from nearby star by its steady light instead of twinkling.
-Did they see very bright Jupiter overhead?
-Did they see extremely bright and yellow Venus?
-Were they able to follow the path of the Milky Way going from south to northeast?
-Were they able to see the Southern Cross constellation?
-Did they make out the shape of the scorpion in the Scorpio constellation?
- During the lunar eclipse, what changes did they see in the brightness of the Moon, and at what time?
- In what part of the Moon did they see darkness (or change in brightness)?
- They should draw the part of the Full Moon that was bright and the part that became dark.
- They should write in their own words to explain what they saw.
During the week that follows, it can be a good time for students to speak about how they enjoyed observing the eclipse and the night sky good time to hear about the even from their pupils and students and to answer questions that are needed.

No comments: