There was a penumbral Lunar Eclipse on the evening of the 9th of February 2009, visible from all of India.
In the extreme western parts of the country, the Moon would have been rising a little under eclipse, while all other parts of the country would have been able to “see” the entire eclipse.
“See” being such an operative word here. For most it seems very difficult to see and discern any difference in a penumbral lunar eclipse. A casual glance does not seem to reveal that anything special is happening to the Moon, although some people say that they can discern some duskiness towards the limb with the slight dimming of the Moon as it falls under the penumbral shadow of the Earth.
What is intriguing is that, even when Earth is able to stop substantial fraction of the light of the Sun from falling on the Moon, but, not cutting off all of it, the Moon still seems bright as usual, with a casual glance.
Imaging the Moon does bring out the dusky shadow of the Penumbra when it is the deepest towards the limb of the Moon. However, viewing it with the eyes - naked eye view or through the eye piece of a telescope, does not easily lead one to detect any darkening of the Moon, in general.
Interestingly, some medieval Indian astronomers like Paramesvara, would caution their fellow astronomers from predicting and telling people about such eclipses as they would not be able to see and discern such eclipses anyway.
From Indian Astronomy - A Source book, by B.V. Subbarayappa and K.V.L. Sharma
That was then. Later, of course, with detecting equipment, penumbral eclipses would have been studied in detail and inferences about the atmosphere of the Earth obtained from these observations.
However, for popular perception, these eclipses continue to remain inaccessible, until digital imaging started showing the faint duskiness of the Moon during penumbral eclipses. This then, has bought penumbral lunar eclipses well within reach of amateur imaging equipment.
It also seems possible to have some quantitative inkling about these eclipses, by an analysis of such digital camera images. In general, digital camera images are not considered good from the point of view of data. However, when it comes to brighter objects like Moon, there will surely be considerable signal remaining, even with the degradation of data from the usage of digital cameras. It would be useful to benchmark digital camera images for obtaining such data, keeping possible student projects in mind.
Nehru Planetarium, Nehru Memorial Museum and Library, in collaboration with the NGO Science Popularisation Association of Communicators and Educators (S.P.A.C.E.) conducted a public skywatch for this intriguing lunar eclipse, from the premises of the Teen Murti House. During the skywatch, live analysis of the images was obtained and the changing brightness of the Moon as it underwent the penumbral lunar eclipse shown as a graph, and the small gathering of visitors in the Teen Murti lawns really appreciated this method of experiencing an occurrence of the eclipse, when visually it seemed as if not much of interest was happening on the Moon.
The eclipse began at 6:06:50 PM and ended at 10:09:39 PM – a very long drawn out penumbral eclipse! It became cloudy around 9:00 PM, when the skywatch was concluded.
The interesting thing about this lunar eclipse was that the decrease in brightness of the Moon, was quite deep for this penumbral eclipse, and this was perhaps the reason why the decrease and later increase in brightness of the Moon as the eclipse approached the maximum and receded, was so easily discernable through the analysis of images obtained with somewhat jugad equipment.
The imaging for the analysis was taken by a Nikon 450 placed behind the telephoto lens seen here. The credit for the imaging goes to the S.P.A.C.E. team and in particular, Chander Bhushan Devgun, Atish Aman and Prashant. Some useful images were also obtained by Balachander, of the planetarium, and included in the analysis. Ashmeet, Rohan and Siddarth from Birla Vidya Niketan, seem to have obatined about a 100 sequential images of the Moon all through the eclipse and these will also be included in the analysis. Some of Ashmeet's images are here http://www.flickr.com/photos/ashmeet Any other images obtained, are also welcome.
The analysis of the images was done by Anurag Garg of the Nehru Planetarium, New Delhi, even as the eclipse was in progress, and the graphs shown to visitors, on a screen through multimedia projection.
Here is an image showing the decrease in brightness as the eclipse approached towards maximum.
The corresponding images of the Moon are shown here in their low resolution version :-
The steps taken to obtain these graphs were the following :- First, the images were obtained using the telephotolens and a Nikon 450D camera - there would have been some degradation of data in that step itself. And then, the jpg image obtained from this was converted to a fits format file using Imagemagick software. Is there any further loss of data in this process? We need to understand this a little more.
IRAF software was then used with the resulting fits format images to obtain these graphs, which are integrating all the brightness along the rows, for every column, in the images shown. Since there was no tracking while imaging, the peak is seen to shift. We will correct for that through programming, once we learn our way a little more with using IRAF.
Here is an image showing the increase in brightness following the maximum phase of the eclipse.
The corresponding images of the Moon are shown here in their low resolution version :-
