22 May 2012

Last Venus Transit of the Century

We have waited 8 years for this event on June 6th this year and if we miss it, its just another 105 years wait for this event to re occur. This event is Transit of Venus, and the last time we observed was on June 8th 2004 and its going to take place again on June 6th this year. In 2004 we could see both Ingress, that is Planet entering Sun's disc, and also Egress meaning Planet coming out of Sun's disc. Many had luck observing the full event but a lot of us had to deal with clouds, as monsoon was just starting.

Since March 26th 2012 after the Greatest Elongation of Venus, we are observing the planet slowly shrinking in altitude in the evening sky and also observing the changing phases of Venus through the telescope, Venus changing from Half lit to Crescent phase and also we have been noticing that the  planet is  getting bigger in angular size and with this we can conclude that Venus is coming closer and in a few days time it will be between the Earth and the Sun.

When Venus comes between Earth and the Sun, the planet is said to be in Inferior Conjunction. On June 6th Venus will be in Inferior Conjunction, this day also happens to be when Venus and Earth lie in the same orbital plane making Sun, Venus and Earth lie in an exact line. When this happens, we can see Venus moving across the Sun's disc, This is called Transit of Venus.

Why  Venus transit does not happen on all Inferior Conjunctions? This is because, Venus's orbital plane is inclined at an angle of 3.39 degrees and only when Venus and Earth line up exactly in this  plane, we can see a transit. The alignment of Earth orbit meeting the Venus orbit happens in the month of June and December, during this time when the planet aligns exactly in line we see a transit. Venus Transits reoccur at intervals of 8, 121.5, 8 and 105.5 years, last was in 2004 and now in 2012, we are going to see it again in 2117 and 2125 both in December.

For our region Venus Transit on 6th June starts at 3:40am so we have to wait till sunrise to see the transit. It would be a wonderful sight to watch sunrise with Venus as a black circular dot in the north on Sun's disc.

Sun Rise at 5:52am

Transit starts
03:40:00 AM
Minimum separation
07:00:00 AM
Sun Altitude 14degrees 30minutes
Transit Ends
10:20:00 AM
Sun Altitude 60degrees 18minutes

Make sure you are in an area where you have clear horizon and its not blocked by buildings and trees. Never look at the sun directly, the best way to observe the sun is through the sun filters.

Ways of observing the event :


Viewing with the help of Binocular:

If you have a pair of binoculars you can fix the binocular on to a stand and project the image of the Sun on to a cardboard or wall and safely watch the Transit. Do not point the binoculars at the sun for long duration at a time. Again NEVER LOOK AT THE SUN DIRECTLY THROUGH THE BINOCULAR use binoculars only to project the image.

Observing with help of telescope:

If you have a telescope, you can use the telescope to project the image of the sun on to a wall or a screen. Before doing that it is advisable to make a mask with small opening that is smaller than the mirror size, like the one shown in the photo and attach it in front of the tube to reduce intensity of the sun and also this will help in increasing the contrast of the image.

This is called an off axis mask.


After attaching the mask you can use the telescope to project the image and observe it safely. 

Every few minutes move the telescope away from the sun so that the heat of the sun does not damage the optical system.

Buy a proper solar filter to observe the sun, do not use sun glasses to see the sun.

Cassegrain telescopes should not be used to project sun, as the internal heat can damage the optical system. 

You can visit transitofvenus.org website for further information on observing advice.

Hope you all have a wonderful observing session this June 6th. Make sure you spread the word and educate people about the Transit.

All the best and Clear skies.