Solar System planets are almost aligned in one plane ( see Table below ) except Mercury, Venus and Pluto.
| Planet | distance | revolution | eccentricity | inclination |
|---|---|---|---|---|
| (A.U.) | (deg) | |||
| Mercury | 0.387 | 87.969 d | 0.2056 | 7.005 |
| Venus | 0.723 | 224.701 d | 0.0068 | 3.3947 |
| Earth | 1.000 | 365.256 d | 0.0167 | 0.0000 |
| Mars | 1.524 | 686.98 d | 0.0934 | 1.851 |
| Jupiter | 5.203 | 11.862 y | 0.0484 | 1.305 |
| Saturn | 9.537 | 29.457 y | 0.0542 | 2.484 |
| Uranus | 19.191 | 84.011 y | 0.0472 | 0.770 |
| Neptune | 30.069 | 164.79 y | 0.0086 | 1.769 |
| Pluto | 39.482 | 247.68 y | 0.2488 | 17.142 |
So the chances of these planets getting aligned with Sun and Earth are rare ( It can happen only when these planets cross the Sun near Ecliptic plane. )
This alignment makes the transit of Venus to occur in pairs. Each pair is 8 years apart BUT the subsequent pair happens after more than a century. ( with a gap of 122 years )
Last occurance in this century was on 8th June 2004 so second one is on 6th June 2012 ( for India ).
And the reason why astronomers are more interested in this year's randezevious is that it is that this transition occurs when the Sun has its solar activity at its peak and so astronomers may be able to observe Venus Outer periphery for atmospheric studies.
If you miss this opportunity now then wait for December 2117 and December 2125 !!
In India we will see this event from about 0702 IST to 1022 IST.
The Venus will enter Sun's disk from about NNW ( equivalent to about 10 o'clock position of Hour hand of a clock ) and transit in front of Sun for abot 3Hrs20Mts and Venus will exit the solar disc at about ENE, i.e. 2:30 position of Hour hand of clock.
( Added after seeing the traffic to this page:
Transit times for US ( all local times ) on 5th June 2012
CA and neighbouring states : 1506 to 1524
UT area : 1605 to 1623
TX area : 1705 to 1723
PA area : 1804 to 1822
Transit times for other countries / Cities :
Germany,Russia,France ( most of Europe ),Cairo : 6th June / 0637 to 0654
Adis ababa : 6th June / 0437 to 0455
Algeria : 6th June / 0538 to 0555
Asia Minor,Nairobi : 6th June / 0737 to 0655
Istanbul : 6th June / 0837 to 0855
China and Neighbouring countries : 6th June 0629 to 1231 ( one of longest visibility in Northern Hemisphere)
Southern Hemisphere has the longest visibility:
Adelaide 6th June 0804 to 1357
Brisbane,Sydney 6th June 0833 to 1426
New Zealand 6th June 1033 to 1625
Tahiti 6th June 1230 to 1526 )
DO NOT WATCH THE SUN DIRECTLY. ( Karna was said to have that ability but you are not Karna ).
Precautions and directions of how to observe the Solar eclipse are reproduced below from http://www.rasnz.org.nz/2012Transit/Venus2012.html
Quote
Whenever the Sun is to be observed safe viewing methods must be used. Any attempt to view the Sun directly could result in instant blindness.
The safest way is to project the image of the Sun onto a suitable screen. Alternatively a suitable, specially designed, Solar filter may be placed in front of the telescope.
It is NOT safe to use a filter at the eyepiece as the focussed heat from the Sun could shatter it.
Unquote
As usual there is a Indian jugaad to see the Sun. But whether that is possible in this digital era is a question.
Take TWO black and white ( X ray films are better ) unexposed negatives ( did someone say 'what is that', not your fault baby , the B&W films are very rare ). Open them in full bright sunlight and keep for full two minutes in sunlight. Then develop these films as usual. After drying you could view Sun through these TWO films held together in front of eye. ( Never try to see the sun thru a single layer of such darkened film.
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