Sunday, June 3, 2012

How to View the Tranist of Venus

If you've been following science news at all, you know there is a transit of Venus on Tuesday. The image to the right is one I took of the last transit of Venus. This is what a transit looks like. Kinda cool.

Having been asked by a couple of folks I thought I'd make a post on how to safely view the transit of Venus which is scheduled for around 22:20 UTC (a little after 6 PM EDT). First off, what not to do. Do not look at the sun with the naked eye, with sunglasses, through binoculars or a telescope that does not have an approved solar filter. Even if you think you can look safely, you can damage your eyes. Likewise, if you have a telescope with a solar filter that fits on the eyepiece end of the scope, throw it out (the filter). They are dangerous. I know someone blind in one eye using one of them.

If you don't have an approved solar filter that attaches to the front of your telescope or binoculars, the best way to view is by projection. This can be used with most small telescopes or binoculars, and is safe. I'm adding a disclaimer that the sun is hot, and when you project it through your binoculars or telescope the inside can get hot. Be careful or you can damage your binoculars, telescope or eyepiece. For that reason I suggest you use cheap stuff, not your million dollar binoculars, for this.

If you have a scope larger than 6 inches or so in diameter consider putting a cardboard mask with a 4" or smaller hole in it over the front. Many scopes come with end caps that have a smaller cap over a 2-3" hole, which you can also use. The problem is that with 8" or more of aperture it is too easy to accidentally burn something (like the inside of the scope). Put a cover over the finer scope, since that can destroy itself by focusing sunlight inside it. If you don't have a lens cap for your finder scope, put a sock or something over it. Put your lowest power eyepiece in the scope, and crank the focuser all the way out. If your scope where the tube can be rotated, turn it so the eyepiece faces down toward the ground.

If you have binoculars, put the front lens cap on one side - we're only going to be using one half of the binoculars, and if you don't over the other lens the sunlight it focuses can seriously damage the binoculars (or you). Focus the binoculars on the closest thing they will focus on.

Next, get a piece of white paper. hold it about a foot from the eyepiece, and aim the binoculars or telescope at the sun. You can't use a finder scope to do this, so the best way to do it is to look at the shadow of the scope or binoculars and make it as small and round as possible. you may have to move around a little to find the sun.
Turn it until shadow is in a line...
Now tilt up/down...
Once you do, try to keep it centered in the field. When it is half out of view, the other half of the sun is heating up the inside of your scope, and can do damage. If you're going to walk away for a minute, cover the front of the scope or move it 90 degrees away from the sun so it doesn't accidentally burn the inside of the scope.

Play with the distance to the paper and the focuser until you get a well focused, decently sized image. If you want, you can make a viewing box to increase the contrast of the image.

To do that, take a cardboard box (mine is something like 8"x16"x30") and cut a piece out of one end. Leave the corners, as it will help the box keep its shape.
Make a projection screen out of white paper or foam board and place it on the end opposite the cut out. You can use the cut out to measure the size of the projection screen.
Line the other 3 sides of the box with something black (I used a tri-fold presentation board made from black foam board). Put it together as shown.
The black sides of the box will keep out stray light, so the projected image of the sun is easier to see.

Enjoy, and if you do see the transit, please post a comment and tell me about it.


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