TWO ECLIPSES AND STAR OCCULTATION BY MOON
Dr Noorali Jiwaji
Do you want to see a star disappearing while you are watching it in the sky? This is your chance to witness an occultation of a star by the Moon. One February 12 just before sunrise the Full Moon will
The Moon is a center of attention this month during three celestial events. Soon after midnight of February 10 going into the morning of February 11 from 1:34 am to 5:53 am the Moon is eclipsed by Earth’s pale shadow in a Penumbral Lunar Eclipse. Second, on February 12, a full Moon will slide across our view of a star a reasonably bright star called ZC1547 from about 5:45 am. The third major event involving the Moon is the Partial Solar Eclipse of February 26 from 6:32 pm to sunset 7:08 pm
The Moon occultation will take place for all places across Tanzania when the Moon begins covering up the star from about 5:45AM on February 12. Start watching near the west horizon from 5 AM and you will see a bright star just above the top edge of the Moon about 20 degrees above the horizon. Over the next half hour, it will come very close to the edge of the Moon and by 5:45AM the star will have disappeared behind the Moon. One hour later around 6:45AM the star will reappear from below the lower edge of the Moon. It will be very close to the horizon.
The pictures below, show how the Moon and star ZC1547 will look at various times before being hidden, at the moment of disappearing behind the Moon, the time of just reappearing from behind the Moon and after reappearing fully from behind the Moon. (obtained using Stellarium software)
The exact times for the beginning of the lunar occultation for some towns in Tanzania, when the star disappears behind the Moon are given below from http://www.lunar-occultations.com/iota/bstar/0212zc1547.htm. The star ZC1547 will reappear below the Moon about one hour after these mentioned times :
To understand why the star remains behind the Moon for one hour, we can note that the Moon moves around the Earth in 29.5 days, so it moves through the full circle of 360 degrees in 29.5 days which is 708 hours. This means that it takes 708 hours to circle 360 degrees around the Earth and so the Moon moves one degree in two hours (708/360 = 1.98 = 2 hrs/degree). The size of the Moon as viewed from Earth is half a degree, that is why the star will be covered by the face of the Moon for nearly one hour.
One day before this occultation event, during Full Moon on February 11 a Penumbral Lunar Eclipse will take place from just after midnight of Friday February 10 from 1:34 am and will last until 5:53 am, just before sunrise. On that night, our Earth will be exactly in line between the Sun and the Moon hence Earth’s shadow will fall on the Moon, but the Moon will not be at the center of the shadow but will be nearer the edge of the shadow where some light from the Sun makes the shadow to be faint. It is a similar eclipse to one observed last year on September 16, 2016. It will pose a similar observing challenge because the shadow will be faint.
Hence start by observing the Moon from around 1 am, just before the eclipse begins, and remember how brilliant the Moon is because it is a Full Moon. Make sure that it is clear of any nearby clouds so that you see it directly. Then watch the Moon after about one or two hours when a big part of the faint shadow is on the face of the Moon and you will be able to notice that the Moon will be fainter than when you observed it at 1 am. Maximum eclipse is at 3:44 am so plan your second observation around that time to observe its maximum effect. You will see that its north west part, which is the bottom right (and brighter) portion of the Moon, will become significantly darker than before the eclipse. This is because that side will be deepest inside the Earth’s shadow and close to the dark umbral part of the shadow.
You can see a good animation of how the eclipse will progress using the free Stellarium software which gives a very realistic view of how the sky actually looks outside. You can also see a good animation at this website: https://www.timeanddate.com/eclipse/lunar/2017-february-11
The third event involving the Moon is a Partial Solar Eclipse on February 26 that will be visible for observers in southern and western Tanzania only between Mbeya and Kigoma. In this region, the Sun will be partially eclipsed from just before sunset 6:32 pm until the eclipsed Sun sets below the western horizon. A good animation of the eclipse can be obtained from the Stellarium software and can be seen at: https://www.timeanddate.com/eclipse/in/tanzania/mbeya?iso=20170226
This eclipse is part of an Annular Eclipse that starts off from South America into the Pacific Ocean and ends in southern, western part of Africa ending as a partial eclipse in Tanzania.
During a solar eclipse the Moon is in between the line from the Sun to Earth, hence the shadow of the Moon falls on Earth. During this eclipse, the main part of the eclipse is an annular eclipse similar to the one that was witnessed in Tanzania last year on September 2016 in the southern regions as a ring and all over Tanzania as a partial eclipse. Only the partial part of this eclipse of February 26 is seen in south and west of Tanzania this time. It is interesting to note that the solar eclipse occurs two weeks after the Penumbral Lunar Eclipse of February 11 because during these two weeks the Moon will have moved from one side of Earth to come between the Sun and the Moon causing Moon’s shadow to fall on Earth.