Solar hurray!!!

Diamond Ring of Solar Eclipse at Varanasi

22nd July, 2009 did create History in India or rather India has become an Iconic Figure(pardon for grammar) in History of Astronomy. It was the moment where Astronomers and others(basically those who do not chase the sky like us) were filled with joy to see the Longest Solar Eclipse of this Century. The last one, which was the longest, in the 20th Century was on 30 June 1973, a whopping 7 minutes and 04 seconds. Eclipse of 22nd July was for 6 minutes & 39 seconds visible in a belt from India to China. There are plenty of details over the net about the same.

Eclipse Path in India

Eclipse path in China

The Eclipse called "Khagraas" meaning Total in Sanskrit, brought the North Eastern & Central cities of India like Varanasi, Patna, Itarsi, Gaya in the domain of Astro-Tourism. I would like to provide some technical details to this spectacular event about which Media had done the same thing which it does easily concealing the truth, create a hooplah! My science enthusiasts though know more than the panelist on the screen. Definitely superstitions have no room any more, but India still has problems in accepting many facts of Science in spite of being the pioneers. Indians knew Mathematics before the West came to know about counting.

For starters, Eclipse, as a common sense, is nothing but a game of shadows as put forward by the 12th Century Mathematician and Astronomer, Bhaskaracharya. Moon comes between Sun and Earth and Moon's shadow falling on Earth creates a momentary darkness. This darkness is called as Totality during Solar Eclipse. Solar Eclipses are partial, annular and total. 22nd July's was a Total Solar Eclipse and was a much awaited one since it was the longest. The maximum possible tenure of Total Solar Eclipse can be 7 minutes and 31 seconds.

History

Eclipses should have been since Earth and Moon systems existed but the scientific interest in Solar Eclipse took a new turn after renaissance. J. J. de Ferror was probably the first one to travel to foreign lands to observe eclipses in 1803 & 1806. He coined the term 'corona' the glow observed during the Totality. Real interest amongst common people started with the work of Mr. Francis Baily, a Finance Guy turned Astronomer in his 50s. in year 1842. He created the hobby of 'eclipse chasing'. When the disk of the Moon covered the disk of Sun, the jagged limb of the Moon's disk due to mountains and valleys, allowed the sunlight to pass through. The thin rin of sunlight was broken up into 'a row of lucid points, like a string of bright beads'. This is now termed as Baily Beads.

Baily Beads

There have been eclipses since then that have been photographed and scienctific experiments carried too. 22nd July's experiment with respect to Solar Eclipse within India have also been substantial from Indian Institute of Astrophysics. A group of Indian Astronomers part of Helios Astronom Group have also been set out for their quest. Details are here.

On 20 May 1919, Arthur Eddington proved Einstein's theory of relativity and that light bends near a massive body like the Sun, was confirmed during this eclipse.

Significance

Well, for starters, Solar Eclipses occur only due to a finite distance and size of the moon. Moon's & Sun's apparent sizes are just the same with respect to Earth. Both appear like a disc in the sky.

Diameter of Moon = 3476 km
Distance of Moon from Earth = 384,000 km
Diameter of Sun = 1.4 million(14 lakh) km
Distance of Sun from Earth = 150 million(15 crore) km

Sun's diameter is 400 times that of Moon but it is 400 times farther than the Moon, hence they appear of same size to us and hence we have Solar Eclipses, else it would have not been possible.

If Moon was some 300 km smaller or few km away from Earth, we would have got Eclipses like they are on Jupiter. Jupiter has 63 moons amongst which 5 are massive but compared to Jupiter their sizes are too small. In short we would have not had total Solar Eclipse if there was a slight difference in sizes or distances.

Things to see during Solar Eclipses:

Corona
Diamond Rings
Phases
Solar Prominences

Critics and also Skeptics will agree with me that since this being a Natural Event and Man can never make it happen, the spectator ship in itself is meant for a marvel. Secondly, it was during these Solar Eclipse is what Helium, the only element discovered, not on Earth. Einstein's theory of relativity was proved. Sun's atmosphere can be studied during this time which is very important to understand Solar Storms, Solar Prominences and temperature variations on Earth, after all Sun is the source of Energy for Life on Earth.

Eclipse's some unknown infos:

Solar eclipse occurs during New Moon Day only
Maximum number of total solar eclipses per year:3
Minimum number of total solar eclipses per year:0
Maximum number of total solar & lunar eclipses per year:7 (with solar more than lunar, always, like 5 Solar & 2 Lunar or 4 Solar & 3 Lunar)
Maximum, i.e. 5 Solar Eclipse seen in the following years: 1805, 1935, 2206, 2709

Duration of Totality of Solar Eclipses

(minutes:seconds)

Longest possible: 7:31
Longest from 2004 B.C. to 2526 A.D. :16 July 2186 A.D. - 7:29
Longest from 2004 B.C. to present : 15 June 744 B.C. - 7:28
Longest in last 2000 years : 27 June 363 A.D. - 7:24
Longest in last 1000 years : 09 June 1062 A.D. - 7:21
Longest in 21st Century 1 : 09 June 1937 - 7:04
Longest in 21st Century 2 : 20 June 1955 - 7:08
Longest in 21st Century 3 : 30 June 1973 - 7:04

Characteristics

Solar eclipse has certain characteristics. An eclipse with similar characteristics takes place after a period of about 18 years. Greeks could predict this and this frequency is popularly known as 'Saros' cycle. To understand saros cycle, consider a total solar eclipse occurs on a specific day then a magic number of 6585 days Sun and Moon will return at the same point. This solar eclipse will occur in the same eclipse season with the positio of the Sun, at the zodiac, is also exactly same as it was 18 years earlier. Both the eclipse are related to each other. Earth moves to 120 degree west, thus eclipse will be visible 120 degree west of earlier eclipse location obviously not from the same location. It is estimated that after 1300 years from the first eclipse no more eclipse will take place from that saros cycle.

Each family of saros lives for about 1315 years.
There are on average 73 eclipses in each saros family.
There are 42 different saros families simulatenously running, each at different stages of evolution.
Each saros is identified by a number suggested by George van den Bergh of the Netherlands in 1955.
According to this numbering system, eclipses occurring at descending node are even-numbered & at ascending node are odd-numbered. 22nd July's Solar Eclipse is numbered saros 136 family. More details are here.

Lot of experiments are being carried by various R & D Org.

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. Hence camps are set at Anji a small hilly area near Hangzhou, China.

For more info on :

References: