Watching the Idd Crescent and a Sky Show of Planets

[njiwaji]

This month once again thousands of eyes will be turned upwards in the west horizon looking for a sacred celestial body. The Moon is the closest celestial body and continually in our eyes at night shifting position and changing shape as it orbits the Earth. The sight of one particular shape, the First Crescent, marks the beginning of the month in many cultures that use the lunar calendar. Muslims will be awaiting the First Crescent to mark the end of Ramdhan fasting and celebrate Idd the following day.

The First Crescent is marked just after the New Moon, when the Moon has moved away from its alignment with the Sun. At New Moon, the Sun is behind the Moon, hence it is impossible to see the Moon because its night side is facing us. Immediately after that, since the Moon moves in its orbit around Earth, the Moon will no longer be in front of the Sun and will have moved slightly eastward, away from the Sun, as viewed from Earth. Once this happens, a small part of the daytime side of the Moon will come into view and forms a very thin crescent very close to the Sun.

When this crescent is visible from Earth, it is termed the First Crescent, which will be thin and close to the horizon so will set within a short time. If the crescent is too thin it will be extremely difficult to see in the bright glow of the atmosphere around the setting Sun and will set before the sky has become dark enough. This month the First Crescent is expected to occur on either Thursday 17th or Friday 18th July. There is uncertainty in our ability to see the First Crescent because it is a very thin crescent that appears very close to the west horizon within the glowing atmosphere around the just set Sun

The key factor for the First Crescent to be able to be seen is that the Moon should get enough time to move in its orbit after the New Moon so that is it sufficiently away from the Sun, and the crescent is large enough and high enough, for the sky to become dark and people have enough time to view it in the west horizon before the crescents gets too low. Since the crescent can only grow with time, once the First Crescent is detectable from one place on Earth, all other places in the world that are west of that location will reach nightfall later hence all other places to the west of the first observed location will also be able to view the First Crescent.

The New Moon this July is on Thursday 16th at 4 am in the morning Tanzania time. So by sunset on that day, 16th, the Moon will have had only about half a day to move in its orbit, which is not sufficient to move it away from the Sun. Hence at sunset on 16th, the crescent will be only 0.4% in size and only 5 degrees above the west horizon, which is practically impossible to see with naked eyes in the bright sunset sky. However, by the next day’s sunset on Friday 17 July, the First Crescent will be 2.4% in size and 16 degrees above the horizon and will set around 7.30 pm. This will allow sufficient time the sky to darken and for people to observe the First Crescent on Friday 17 July and we can expect the first day of Idd to be celebrated on Saturday 18th.

The brilliant Venus-Jupiter pair has changed places after coming closest at the beginning of the month. Venus shines ever brighter now as it moves closer to Earth in its orbit around the Sun. Through even a telescope or binoculars, Venus is seen as a thin crescent growing thinner by he day. However since the planet is getting closer to us, its angular size is getting bigger and bigger making it shine brightly in spite of its crescent getting thinner.