June 5, 2012 Venus Transit

With the transit of Venus approaching June 5, 2012 many astronomers are gearing up to see the event.

I have spent several hours trying to educate myself about telescopes and filters needed to view the transit.

The consensus is that you should use a front end filter on your telescope for direct viewing instead of an eyepiece only filter. The front end filter reflects 99.999% of the suns light and heat energy away from the tube unlike the ep filters that magnifies heat and light in the same fashion as a magnifying glass focuses a beam of light to create a burning hot spot of light.

The continental USA will only see a small part of the 5-6 hour for the complete transit. In Arkansas the transit starts about 5:08pm and sundown is 8:17pm. When the transit starts the sun will be 36° above the horizon. By the time Venus is inside the suns sphere another 22 minutes have passed and the sun's altitude will be about 5° less. You WILL need to find a viewing site that has a low western horizon. As you move farther west the view gets better.

FILTERS

There are three types of front end filters, coated glass, coated mylar film, and coated polymer film. Glass being the most expensive type. Manufacturers of the film filters include Baader, Thousand Oaks, and Seymour Solar and they sell sheet film for those who like to DIY. The Mylar filter produces a bluish image, the polymer a yellow/gold image. Always check the filter for "leaks" before using because the damage to your eyes is irreparable. I purchased a 9" x 10" sheet of Seymour Solar "black polymer" for $12 that they sell on Ebay.

TELESCOPE

A refractor is the preferred type of scope. A 60-90MM refractor with 15-20MM eyepiece should be fine. There are telescopes exclusively designed for solar viewing. These scopes are the refractor type and some have special features to siphon off the heat from the tube.

SUN SHADE

A sun shade is needed to block the sunlight. The shade is a 2'x 2' piece of cardboard with a hole in the center that allows it to fit over the aperture of your scope. The shade will prevent ambient sunlight from ruining your view in the eyepiece or washing out your projected images.

FINDING THE SUN

Finding the sun without a finder scope can be a bit time consuming. The method I use is get the Alt/Az. from Starry Night computer program then use a wood workers angle finder to set the altitude and a magnetic compass to find the azimuth. It works pretty well. I just happened to own a Dasco Pro Angle finder which is sold online by Amazon. You can also use a protractor with a string and weight to set the altitude.

SAFETY

The safest viewing method is eyepiece projection. It does not produce as good results but it is eye safe. Safe to the telescope, I am not sure especially for long periods.
I think the coating on the lens, mirrors or eyepieces can be damaged? Small refractors or binoculars are preferred because the heat buildup isn't as great as when using larger apertures. To appreciate how hot the light coming out of the eyepiece is place you finger behind the eyepiece for a few seconds. Now imagine your eye back there !!!!

The projection method I use is to remove the solar filter and place a white sheet of heavy paper behind the eyepiece. Move the sheet away from the eyepiece to get the best image detail and size.

Remember that safety is paramount! Solar viewing is dangerous if not done in a safe manner. BE VERY, VERY CAREFUL.

DISCLAIMER

I am not an expert at solar viewing but rather a newbie. The information above was gathered from the internet to help me try my hand at the transit. I have been an amateur astronomer for 7 years and my primary interest is astrophotography and my favorite target is comets.

James C
Arkansas

Links:

http://transitofvenus.nl/wp/where-when/local-transit-times/
http://transitofvenus.nl/wp/observing/build-a-sun-funnel/
http://sohowww.nascom.nasa.gov/
http://www.skyatnightmagazine.com/feature/how-guide/how-to%E2%80%A6-make-solar-projection-screen