Udupi: Treat Awaits Skygazers - Total Lunar Eclipse on Dec 10
Dr A P Bhat - Co-ordinator of Poorna Prajna Amateur Astronomers' Club, PPC Udupi
Udupi, Dec 9: One of the best sky events of this year will be the lunar eclipse on Saturday December 10, when the full moon passes deep into Earth shadow. The total eclipse will occur between 7.36 pm to 8.27 pm for 51 minutes. The eclipse will start at 6.15 pm and end at 9.52 pm
A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur on the night of a full moon. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes. Unlike a solar eclipse, which can only be viewed from a certain relatively small areas of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth. A lunar eclipse lasts for a few hours, whereas a total solar eclipse lasts for only a few minutes at any given place, due to the smaller size of the moon's shadow.
The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the Sun’s large angular size, solar illumination is only partially blocked in the outer portion of the Earth’s shadow, which is given the name penumbra. A penumbral eclipse occurs when the Moon passes through the Earth’s penumbra. The penumbra causes a subtle darkening of the Moon's surface. A special type of penumbral eclipse is a total penumbral eclipse, during which the Moon lies exclusively within the Earth’s penumbra. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon.
A partial lunar eclipse occurs when only a portion of the Moon enters the umbra. When the Moon travels completely into the Earth’s umbra, one observes a total lunar eclipse. The Moon’s speed through the shadow is about one kilometer per second (2,300 mph), and totality may last up to nearly 107 minutes. Nevertheless, the total time between the Moon’s first and last contact with the shadow is much longer, and could last up to 4 hours. The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse’s duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease appreciably within the changes in the orbital distance of the moon. Thus, a totally eclipsed Moon occurring near apogee will lengthen the duration of totality.
The Moon does not completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth’s atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The red coloring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth’s atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the air molecules and the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish color; an alternative way of considering the problem is to realize that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind the Earth.
The amount of refracted light depends on the amount of dust or clouds in the atmosphere; this also controls how much light is scattered. In general, the dustier the atmosphere, the more that other wavelengths of light will be removed (compared to red light), leaving the resulting light a deeper red color. This causes the resulting coppery-red hue of the Moon to vary from one eclipse to the next. Volcanoes are notable for expelling large quantities of dust into the atmosphere, and a large eruption shortly before an eclipse can have a large effect on the resulting color.
The moon likely will take on an orange red colour during totality as a small amount of sun light passes through earth atmosphere and scatters on to our only natural planet at totality.
Poornaprajna amateur astronomers club of Poornaprajna College has arranged a programme in collaboration with Sky Telescope Mumbai with their Telescope to watch this wonderful event on the top of MBA building of PPC, from 6 to 9 pm on December 10 for the students and public.
On this occasion, various puja programmes are being organized at different temples. At 11 am on December 11, Panchamrita Abhisheka and special Maha Puja will be held at Kudroli Lord Gokarnanatha Temple. A release by the temple said that as per astrological calculations, this eclipse bodes negative affects for people born on Hindu zodiac signs, Vrushabha, Mithuna, Tula, Kumbha and Dhanu. It has advised such people to get the adverse affects of the eclipse nullified by performing religious rituals like Ganapati Puja, Gana Home, Shiva Puje, Abhisheka, Navagruha Puja, Tiladana, Anna Dana etc and by visiting temples and praying to the Almighty.