Transit of Venus - 2012
The universe is a collection of
Planets, Stars and numerous other celestial objects which move in the vastness
of the space surrounding them giving rise to several interesting celestial configurations,
such as Eclipse, Transits, Occultation etc. Among these, eclipse is common and
easily understood whereas transit is rather rare hence not heard very often. But
here is a chance, not only to learn but to see (with naked eye) a rare Transit
of Venus on June 6th, 2012.
Venus, our immediate neighbor planet in
the solar system has been known in the prehistoric times as two separate
objects namely the morning star and the evening star. The Babylonian cuneiformic texts such as the Venus tablet of Ammisaduqa, dated 1581 BC
however described it as "bright queen of
the sky” suggesting the two were indeed a single object and named it Ishtar (Sumerian Inanna), the
personification of womanhood, and goddess of love and beauty. As such Venus, apart
from being the brightest object after Sun, became the only planet in the Solar
System to be assigned a feminine name.
Also, Venus being a terrestrial planet have some physical
feature semblance to Earth, thus it is
also called Earths sister or twin. Venus however revolves around the Sun in a retrograde
motion on the inside of Earth’s orbit hence called an inferior planet. Therefore
during the course of revolution, there is possibility of Venus passing directly
between Earth and Sun, constituting a syzygy. During such a time, Venus though
larger in size but since situated much farther away, it does not completely block
the sun, instead appear as a small black dot (moving) on the face of the sun.
Such celestial occurrence wherein one apparently
small celestial body appears to
move in front of another apparently large celestial body, hiding a small part
of it is termed as Transit. The inferior planets, namely Mercury and Venus are
known to transit across the disk of the Sun.
Unlike transit of Mercury which occurs 13 – 14 times in a
century, Venus transits are rare since the orbital plane of Venus is tilted 3.4o
compared to Earth’s orbit. This orbital tilt causes Venus to apparently pass under
(or over) the Sun during normal (inferior) conjunction. Morever the orbital
period of Earth (365.2 days) differs from that of Venus (224.7 Earth days)
which is why Venus rarely arrives at a common point with Earth. It is only when Venus reaches conjunction
with the Sun near its nodes, (the longitude where Venus passes through the
Earth's orbital plane/the ecliptic)
a transit occurs.
In the past, Transit of Venus is known to have been observed only
on 6 occasions beginning 4th December 1639, 5th June 1761, 3rd June 1769, 8th December 1874, 6th December
1882 and the last transit was observed on 8th June 2004. Those who
missed the 2004 event can witness the spectacular phenomenon for the last time
on 6th June 2012. Since the next transit of Venus will occur after a
gap of 105 years on 11th December 2117.
There are four named "contacts" during a transit namely the External Ingress (Venus entirely outside the disk of the Sun, moving inward), Internal Ingress (Venus entirely inside the disk of the Sun, moving further inward), Internal Egress (Venus entirely inside the disk of the Sun, moving outward) and External Egress (Venus entirely outside the disk of the Sun, moving outward). A fifth named point is that of greatest transit which marks the halfway point in the timing of the transit.
The forthcoming transit (all four contacts) would be visible
from northwestern North America, Hawaii, the western Pacific, northern Asia,
Japan, Korea, eastern China, Philippines, eastern Australia, and New Zealand. The
transit will already be in progress at sunrise for observers in central Asia,
Middle East, Europe, and eastern Africa. Due to the International Date Line the Western Hemisphere will see the transit on 5th June.
At Port Blair the transit will be visible
from sunrise (at 4h 56m IST) till External
Egress at 10h 20m 33.7s. A detailed
list of circumstances for other locations in India is available on the website
of Positional Astronomy Centre, Kolkata.
Venus transits are of great scientific importance especially
with reference to the first realistic estimate of the size of the Solar System.
Observations of the 1639
transit, combined with the principle of parallax, provided a fair estimate of the distance between the Sun and the Earth (Astronomical unit).
The 2012 transit of Venus, unlike the 2004 event occurs
during an active phase of the 11-year activity cycle of the Sun, hence it is
likely to provide scientists numerous research opportunities, particular in
regards to the study of exoplanets and open up new vistas in astronomy.
General public out of curiosity will be
tempted to look directly at the Sun during the transit, but note that looking
directly at the Sun without proper protection is harmful for the eyes. Also
viewing Sun through optical devices such as binoculars, telescope, or through a
camera viewfinder, exposed X-ray film, CD’s etc are equally
harmful and not advisable. The once-recommended
method of using exposed black-and-white film is not considered safe anymore.
Approved solar filter, Shade # 14, welder’s glass or eclipse viewing glasses coated with a vacuum-deposited layer of chromium are
considered safe to view the Sun or the transit. Indirect projection method such as
Pin Hole Camera is the best to
observe such events. Children viewing the event are required to be supervised
by an informed adult. Local Science Centre is the best place to observe such
events. They not only educate and guide the observers but facilitate safe
viewing of such astronomical phenomenon.
References :
4) http://quantumphoenix.net/2012/05/23/
A radio talk based on this post was broadcast over AIR Port Blair on June 2nd at 0820pm.
The post was also carried in the Echo of India dated 5th June 2012
A radio talk based on this post was broadcast over AIR Port Blair on June 2nd at 0820pm.
The post was also carried in the Echo of India dated 5th June 2012
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