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The 2012 International Transit of Venus

Re-observation

 

Undergraduate Thesis 2009 by Matthew Cooper

Supervised by Dr Craig Roberts

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Venus in transit *

 

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Observing conditions

 

Observer safety during a transit

Because observing a transit of Venus requires observing the Sun, the activity is inherently dangerous. There are two methods of safely observing the Sun: use a solar filter on a telescope and view the Sun directly, or set up a telescope aimed at the Sun to project the image through the eyepiece onto a piece of paper or similar flat surface.

Observing the Sun directly with the naked eye has been proven to cause eye damage, particularly from the near-infrared component of the Sun’s radiation which causes burning of the retina (Chou, 2005). A solar filter should be chosen that allows comfortable viewing of the Sun, while reducing visible light and infrared radiation to a safe level. According to Chou, a safe solar filter should transmit less than 0.003% of visible light (380 to 780 nm wavelength) and no more than 0.5% of near-infrared radiation (780 to 1400 nm wavelength).

An example of a safe solar filter that would be applicable for observing the transit of Venus through a telescope is the Baader Astro-Solar filter sheet.

Where the transit will be visible

The chart below illustrates where throughout the world the transit of Venus can be observed in 2012. Eastern Australia is an ideal observing location for this transit, as the entire transit will be visible from there. Much of eastern Asia, Indonesia, New Zealand and Russia will also be able to view the entire transit.

Locations where only ingress or egress is visible may still be able to time these events (with exact UTC timing) and contribute observations to make estimations of the AU using Delisle’s method.

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Figure 18 – Visibility of transit (NASA 2009)

Note: Where transit is in progress at sunrise, these locations have missed the first contacts. Where transit is in progress at sunset, the last contacts are not visible.

Sunshine probability and choice of observing location

Since a clear sky is essential for performing transit observations, the best observing locations should be places that have the highest expected proportion of sunny days during the time of year when the transit occurs (June in 2012). The chart below grades parts of the world according to probability of sunshine during June.

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Figure 19 – Sunshine probability in June (Westfall 2004)

As is evident on the chart, the Northern Territory of Australia has the highest probability of sunshine, making this a prime location for transit observations. All of Queensland has a good chance of sunshine, while the further south along the East side of Australia, the lower the probability of sunshine gets. East Asia, while a prime viewing location as far as position during the transit, experiences humid rainy weather during June, which is their summer. As a result probability of a clear sky is low over much of this region (less than 40%).

 

 

Quick Facts about the 2012 Transit of Venus

 

Transit will commence at approximately 22:00 (Universal Time)

 

Transit duration will be about 6 hours 40 minutes

 

(Times above are approximate and will vary according to observer’s location)

 

For Sydney:

First contact: 8:16 AM

Last contact: 2:44 PM

The transit and the distance from Earth to Sun

History of transit observations

Observation methods

Observing conditions

Collaborating data

References

Contacts

 

 

 

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Matthew Cooper 2009

Last modified 30 October 2009