New Delhi:
1. The total lunar eclipse on the intervening night of July 27 and 28 will last for 103 minutes and thus be the longest lunar eclipse of the 21st century. The longest total lunar eclipse of the previous century happened in its last year, on July 16, 2000. It had lasted nearly four minutes longer, at an hour and 46.4 minutes.
People in Asia and Africa will have the best views of the eclipse. Those in Europe, South America and Australia will see partial views. It will not be visible in North America and Antarctica. In India, the eclipse will commence at 22:42:48 hrs on July 27 and end at 05:00:05 hrs on July 28.
2. The alignment of the centres of the Sun, Earth and the Moon, and the distance of the Moon from Earth at the time of the eclipse, combine to determine its duration. On Friday night, the centres of the three celestial bodies will be in an almost straight line, an arrangement called a syzygy. The Moon will also be near its farthest point from Earth – i.e. apogee – and so appear to be at its smallest. As a result, it will take the natural satellite more time to cross Earth’s shadow, making the eclipse last longer.
3. While the ancient Hindu religious texts claimed that eclipses were caused by demons devouring the Sun and the Moon on occasion, Aryabhaṭa (476-550 CE) provided a scientific theory c. 499 CE. He established that when Earth comes in between the Sun and the Moon, Earth’s shadow covers the Moon, resulting in a lunar eclipse and that when the Moon is in between the Sun and Earth, the Moon’s shadow on Earth causes a solar eclipse. Hence, lunar eclipses occur only on a full-moon day, when the Sun and the Moon are on opposite sides of Earth, and solar eclipses occur only on a no-moon day, when both are on the same side of Earth.
Editor’s note:
– According to the authors of the chart above, “The unevenness of the data is partly due to social upheavals and partly due to non-uniform scanning of the records over the period”, and that “the true records must be several times this data”.
– Over 15 centuries after Aryabhata’s exposition, many religious personalities continue to perpetuate detrimental myths. For example, one must not eat during an eclipse because, according to Jaggi Vasudev, “nourishing food turns into poison”. His words came shortly after the death of Yash Pal, the eminent scientist and science communicator who had spent a lifetime debunking pseudoscience and fighting its effects on the social fabric.
4. Eclipses are nothing but shadow play: during a lunar eclipse, the Sun gets behind Earth from the Moon’s POV, and Earth’s shadow falls on the Moon’s orbit. No ‘mysterious rays’ emanate from any body. It is completely safe to watch a lunar eclipse and no special equipment is required to mediate this experience. However, one should take precautions when watching a solar eclipse because of the brightness of the Sun.
5. Although light from the Sun cannot pass through Earth’s bulk, the thin atmosphere enveloping the planet permits light to penetrate as well as refracts the rays towards the Moon. So when most of the blue light from the Sun is filtered out by the atmosphere, the sky appears blue, and the least-scattered red light seeps through to reach the moon and makes the celestial body look red. On July 27, as the centres of the Sun, Earth and the Moon will be in near-syzygy during the total eclipse phase, only a minimal amount of sunlight will pass through the atmosphere. Consequently, the Moon will appear dark.
6. Take a one rupee coin and look at the shadow cast by it: the central part of the shadow would be dark but towards the edge, its strength is lower. The darker part of the shadow is called the umbra region and the lighter part, the penumbra. Likewise, Earth also casts both umbral and penumbral shadows.
To the untrained eye, the Moon’s entry into Earth’s penumbral shadow region at about 10:53 pm will not be noticeable. However, as more of the Moon’s disc is covered by the penumbral shadow, a steady decrease in brightness will become apparent.
At about 11:54 pm, the Moon will enter the umbral shadow. This is the most dramatic part of the eclipse, when a seemingly sourceless darkness slowly and steadily engulfs the face of a full Moon.
7. On July 27, the night sky will also be graced by a brighter Mars thanks to its being very close to Earth this time of the year.
8. At around 12:30 am, totality will begin. For the next hour or so, the Moon will be completely inside Earth’s shadow.
9. Normally, there is no perfect or even quasi-perfect syzygy, and light escaping through Earth’s atmosphere makes the Moon look more reddish than it actually is. But thanks to the eclipse, the Moon will be dark – so dark, in fact, that at and approaching 1:51:27 am on July 28, it may not be even visible. That will be the peak of the total lunar eclipse. After this point, the Moon will begin to re-emerge from the dark side.
10. In a year there can be as many as seven eclipses and as few as two. They can occur in the combination of four solar and three lunar eclipses or five solar and two lunar eclipses. If there are only two, then both of them will be solar eclipses.
With inputs from the Public Outreach and Education Committee of the Astronomical Society of India.
T.V. Venkateswaran writes for India Science Wire and tweets at @TVVen.