Would any one like to be in the place
where everything is static, where there could be no change?
Horrible!!
Would like to run away from that place…
Is it that, even the universe gets bored if it is static?
Take for example, our solar system. All
planets move around the Sun. The mystery is caused because orbits of the
planets are not in single plane. More important than that is the orbits of
different planets are not circular but elliptical with different eccentricity
for each planet.
When
so many objects are revolving around another object, a natural consequence of
the motion is obstruction of one object as seen from another. Obstruction in
this sense just means blocking of one object by another.
So, what are the different types of
possible obstructions?
1) Eclipse:
Obstruction in which the object which is
being obstructed and the object which is obstructed appear nearly to be of same
size as seen from the third object.. (It’s
only the appearance, and not the real size)
Example:
Lunar and Solar Eclipses.
2) Occultation: Obstruction of a small body by a
larger one is Occultation.
Example: Occultation of a star, (like
Sirius, Regal…) by moon. Or occultation of planets by Sun.
3) Transit: A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body,
hiding a small part of it, as seen by an observer at some particular vantage
point.
Each of the above 3 are possible only
when all the 3 celestial objects (the obstructing body, the body which is being
obstructed and the object where the observer is) are in the same line.
For any one of these cases to occur, the
following condition has to be satisfied.
- · Obstruction is possible only when the 3 objects align along the node. [Nodes are the points where two orbital planes intersect]
- · Both the revolving bodies must arrive to the nodes at the same time.[or should be within some angular separation such that the shadow of one falls on the other].
Let us come to the topic of transits. Is it possible
to see transits of all planets?
For an observer on Earth, there can be only 2
transits, that is the transits of Mercury and that of Venus. If it is possible
such that there is someone on any other planet say Jupiter, he can see the
transits of Mercury, Venus, Earth and Mars provided the conditions for transit
are satisfied.
In general, it is possible to see the transit of all
the planets whose orbits lie inner to the orbit of the planet where the
observer is.
With respect to the observer on Earth,
there is a transit on June 6th. So let us have a look at its importance, what
makes it rare and such other things.
All
the inner planets undergo inferior and superior conjunctions during their revolution.
Inferior Conjunction:
Conjunction
in which both the planets lie on the same side of the Sun is called inferior
Conjunction.
Superior Conjunction:
Inferior
planet becomes invisible, when it is on the opposite side of the Sun, as seen
from a planet that is superior.
Copernicus was able to show that, the synodic
period (S), the sidereal period of the planet (P) and the sidereal period of
the Earth (E) are related by the formula:
1/S = 1/P -1/E for inferior planets
1/S =1/E – 1/P for superior planets.
For Venus and Earth, P = 224.5 days, E=
365.25 days. Therefore, S nearly equals to 584 days, which means there occurs
conjunction every 584 days.
Formation of Pentagram by Venus:
When
the successive conjunctions of Venus are traced, the pattern forms a pentagram
or pentacle as shown below.
8 years are
required for the complete formation of pentagram.
The orbital plane of Venus makes an
angle of 3.4 degree with the ecliptic. Thus transit of Venus is possible only
during early December and June when Venus passes across the orbital nodes.
So once in 8 years, there has to be a
transit. But,
8 years =8 x 365.256 days = 2922.048
days.
5 synodic periods = 5 x 583.9 days =
2918.5845 days.
The
difference is 2.46 days. This implies
that after 5 synodic periods, the Earth will be ahead of previous configuration
by 2.46 days. Equivalently planet Venus would have moved by22’(arc minutes). [A unit of angular measurement equal to one sixtieth (1⁄60) of one
degree]
Thus the pentagram formation shifts by
22’. This is as shown pictorially below.
Transit of Venus
shows a clear pattern of recurrence at intervals of 8 years, 121.5 years,
8years and 105.5 years.
Note that there is a shift in the position of
Venus by 22’in each pair of transit. As the angular size of the Sun is 30’,
next conjunction may or may not be a transit. Venus may appear outside the disc
of the Sun and miss transit.
The first recorded transit of Venus was
done by Jeremiah Horrocks and William Crabtree during the 1639 transit.
The importance of transit was it served
as a tool in calculation of value of 1 AU {Astronomical Unit- Distance between
Sun and the Earth}
It was done by using the method of
parallax, just by measuring the angle at two different positions of the Earth,
as shown below.
Black Drop Effect:
The phenomenon in which a thin drop like
structure appears between 2 limbs (apparent edges of Venus and Sun) when Venus is about to cross the
limb of Sun, just after second contact and gain just before 3rd
contact.
When you hold your fingers against a bright
background and slowly move so that they touch, you will observe a phenomenon
similar to the black drop effect.
How to safely observe the transit?
·
Wear
approved solar filters.
·
Pinhole
projections / Pinhole mirrors.
·
Binocular
projections / telescope projections.
.. . . . . . . . . .
LETS NOT MISS THIS UNIQUE OPERTUNITY !! J
Article by:
SANDHYA N.K
Under the guidance of
SIR H.R MADHUSUDAN
REFERENCES:
·
TRANSIT OF VENUS – BY DR B.S SHYLAJA
No comments:
Post a Comment