Editorial Note: With a partial solar eclipse being visible in select parts of North America today it is a good time to re-cap one of our older posts about how to project and image of the sun onto cardboard using a telescope or binoculars. Sadly given that we are still in a Nor’Easter here in the Philadelphia region we will probably not be able to enjoy the eclipse. So be sure to view it for us if you are able:
With the just passed annular eclipse out in the Western part of the USA a couple of weekends ago and the upcoming transition of Venus you might be inclined to buy a fancy solar filter for that telescope.
Well there might be a problem with that. See everyone else had the same idea as you, and that means the manufacturers of such filters are pretty much out of stock! It can even be hard to find just the filter material! What to do?
Well, there is another way of viewing the sun without the use of a filter. It can be tricky and it can be dangerous if proper care is not taken. That method is called projection astronomy. This is where you use the telescope & eyepiece to actually project the image you would normally see with your eye onto a board or other bright surface.
What do you need? You need a telescope with an eyepiece (preferably lower-medium powered), a sunny day, and something to project the image onto.
We came up with this kind of last minute, so we just used a flat box on a clipboard. It had problems with the box seams, but the surface was very bright (brighter than the average piece of printer paper) and so would give a decent image.
Next up, we need a telescope. We used an Orion StarBlast 6 , mostly because that is what we had around the store.
Note that the picture above shows the telescope in action. When setting it up and aiming it you should LEAVE THE DUST COVER ON. This is the best thing for your safety.
Aiming your telescope at the sun is pretty easy, just try to get your tube to make the smallest shadow possible. When you think you are on target, remove the dust cover and see if there is any light coming through the eyepiece. DO NOT look into the eyepiece, ALSO DO NOT LOOK DOWN THE AT THE EYEPIECE. View it from the side. We are not responsible for your losing your eyesight!!!
Now a further safety warning: Try to avoid getting any body parts in the path of the light coming out of the eyepiece. Hold the board on the edge, work around the telescope, not over it, etc.
So now that you are lined up with the sun, you can see what kind of image you have. Place the projection board about a foot or so away from the eyepiece. Move it closer or further away to try and get it into focus. DO NOT bring it closer than 6 inches from the eyepiece, the light is a little too concentrated there and some types of paper might burn.
Some adjusting will be needed. It is best to move the screen rather than the telescope. If you must adjust the focuser, put the dust cover over the front of the telescope.
So what kind of view so you get? Well, here is a shot of the screen that is a little closer than the last photo:
This didn’t show up too well in the photo, but if you look closely, you can see some sunspots projected on to the board to the right and right/down of the center.
How well will projection astronomy work on the transit of Venus? We don’t know for certain. The sun will be very low in the sky and there may be more distortion or discoloration as a result. But if you have the time and the telescope, this isn’t exactly an expensive experiment! Just remember to be careful! Pointing a telescope at the sun always has risks – just use common sense and keep out of the path of the projected sunlight and you should be fine!