Total solar Eclipse of July 22, 2009

On Wednesday, 2009 July 22, a total eclipse of the Sun will be visible from within a narrow corridor that traverses half of Earth which includes most of eastern Asia, and the Pacific Ocean. The total solar eclipse of 22nd of July 2009 will be the longest eclipse of the 21st Century being 6 minutes 38 seconds at the point of maximum eclipse. The occurrences of total solar eclipses are still important, not withstanding the invention of coronagraph in 1930 and number of space instruments launched in space to make the observations of solar corona in EUV, soft X-ray and low resolution broad band images. The total solar eclipses provide minimum of scattered light about 1000 times less than that in the coronagraphs. Also observations can be made with high spectral, spatial and temporal resolutions as compared to those of space base instruments because large and heavy equipment can be used in ground base observations.

The temperature in the solar corona rises to million degrees from about 5700 degrees at the photospheric level. Some models have been proposed to explain the heating of solar corona but the existing models are unable to explain all the physical and dynamical properties of the solar corona. It has been recognized that magnetic fields play an important role in heating up the plasma in the solar corona but identification of the process or processes still remains an open question. It has been proposed that occurrence of micro or nano flares at the surface of the sun can create shock waves and contribute to the heating of solar corona but some have argued that these waves get dissipated in the chromosphere itself and cannot reach the corona. The existence of fast or slow mode magneto-hydrodynamic waves in the solar corona is expected to cause intensity and velocity oscillations in the solar corona in the range of 1 Hz and lower frequencies. Many attempts have been made to detect these oscillations but the results are contradictory. A large number of small-scale reconnections have also been proposed to explain the heating of solar corona. Another way to heat the solar corona is to generate waves through turbulence (acousting waves). The existence of non-thermal motion in the solar corona and its variation with height has also been interpreted to cause heating of the plasma in the solar corona.

Path of the total solar Eclipse of July 22, 2009

Figure 1. Path of the total solar eclipse in India on July 22, 2009.	Figure 2. Path of the total solar eclipse in China on July 22, 2009.

The interactive Google map for the path of totality

The total solar eclipse will be of longest duration during this century. It will be visible in India, some of the Japanese islands, China and Pacific Ocean. The eclipse begins with the sunrise in the western part of India, travels to eastern part of India, crosses to Myna-mar (Burma), small islands of Japan and China. In India Surat, Indore, Bhopal, Jabalpur, Varanasi and Patna are some of the cities lie close to the central part of the totality. In China duration of the totality will be about 5 minutes. In India altitude of the sun will be about 15 degrees in the eastern part at the time of total eclipse and this period is full of rains due to South West monsoon.

Imaging of the solar corona has the advantages of providing the information over two dimensional region of the solar corona but it may have the small uncertainty of in the data due to variations in the sky transparency. On the other hand spectroscopy provides data only on the small portion of the solar corona but with spectral purity and is possible to account for the variations in the sky transparency. Line profiles can also yield information about the temperature and non-thermal structure of the solar corona.

We, therefore, have proposed to perform spectroscopy and imaging of the solar corona in the green and red emission lines. We hosted a one day national meeting for the preparation of the total solar eclipse at Bangalore. 

EXPERIMENTS PLANNED DURING 2009 ECLIPSE

To study the  existence of waves in the solar corona and their nature we  have proposed to conduct the following experiments:

Spectroscopy of the Solar Corona:

A 30 cm two mirror system (coelostat) will be used to direct the sun & coronal light to a 10 cm objective to form an image of the corona on the slit of the Littrow type spectrograph. A 14 cm objective will collimate the beam and image the spectrum on the two CCD cameras. Broad-band filters will be used too separate the orders. A grating with 600 lines per mm blazed at 2 microns will provide a reasonable dispersion (2 Angstrom per mm) to determine the emission line profiles. Two CCD cameras of 1K x 1K format with pixel size of 13.0 x 13.0 microns will be used to take the images. The CCD chip will be back illuminated for high efficiency and camera will operate in frame transfer mode to obtain data with high frequency. The read out will be in 16-bit format at 5 Hz. Initial tests with the equipment indicates that we shall be able to able to take the spectra of the solar corona at a frequency of about 5 Hz with an exposure time of 200 ms.

Photometry of the Solar Corona:

Two 40 cm telescopes with effective focal length of 200 cm each will be used to image the solar corona. A 5 cm narrow band (3 A) filter centered around 637.4 nm kept near the focal plane in one of the telescope will permit to take images of the solar corona in the red emission line. The second telescope fitted with 530.3 nm narrow band filters will permit to take the images in the green line. The CCD cameras of 2K x 2K format with 13.5 x 13.5 micron pixel size will cover the solar corona up to 1.5 solar radii where most of the emission occurs. The 16-bit read out at 5 MHz rate and will provide high dynamic range and fast kinetic series. The back illuminated chip will yield more than 90 percent efficiency at the wavelengths of interest. After binning the CCD pixels by 2 x 2 we expect to get the images at the rate of about one frame per second with an exposure time of 200 ms.

Location of the observations:

Keeping in view the prevailing weather conditions along the path of totality and altitude of the sun at the time of the epoch of the eclipse, it appears that the chances of viewing the eclipse from Indian parts are small and about 60 percent in parts of eastern China. We have planned to set up a camp at Anji a small hilly area near Hangzhou, China.

Figure 3.40-cm telescope being tested at the Vainu Bappu Observatory at Kavalur to perform the imaging of the solar corona with frequency of about 1 Hz.	Figure 4. Setup for spectral observation.