Solar Eclipse

There was a solar eclipse yesterday over the western US.  Hawai'i was in line to catch part of it in the afternoon (about 18%, less than 1/5, of the sun blocked by the moon at its peak).  We prepared for the eclipse with some indirect viewing equipment.  (T and I also ran by two hardware stores early in the morning to look for shade 14 welding goggles, but they didn't have any that dark.)  The sky was clear in the morning but in the afternoon thick clouds rolled in.

What was frustrating was there were no clouds out over the ocean, just over land.  This is pretty typical here.  The air moving to higher elevation over the islands creates clouds which melt away as the air descends again over the ocean.  The ancient Polynesians used this to find islands over the ocean.  Often if the land was not visible just over the horizon the clouds over it would be.  (This also reminds me of how we found lakes on a canoeing trip in Ontario.  If you looked for it, there was a subtly lighter shade of blue in the sky over lakes, because of the reflected light compared to darker spruce forests, so you could tell approximately where to look for the portage (path) to connect to the next lake.) 

While we waited, M sat in the window and drew what she imagined the eclipse might look like.

Then a small break opened up in the clouds and we ran out to get a look. 

Of course you can't stare at the sun, so I used a camera lens to focus an image onto a piece of paper on the ground, in this case held firmly by M's feet.  In the middle of the image above you might be able to see a dent in the side of the sun from the eclipse. 

Here is a closer shot (click to open a larger image in the browser).  The problem with the image is the clouds around the sun are also reflecting a lot of light, so it is hard to make out the shape precisely (look for the bite taken out of the bottom of the sun).  Also I realized we had power lines between us and the sun so we moved to a better spot but the clouds closed back up.

Waiting for the sun...

Finally there was another break in the clouds and we were able to image the sun again with a dent in it. 

For a while it was bright enough to try out our pinhole camera viewer (made out of aluminum foil, a cardboard box, a piece of paper and some tape).  A big advantage of lenses is that for each point in the image light is collected from a large area the size of the lens to make the image.  In general this gives lens focused projections a huge advantage, especially in low light.  A pinhole camera uses light from a small point to make the image, but has the advantage of being simple and always in focus.  (And they can be a lot of fun, I made a pinhole camera out of a shoebox years ago when I worked for a printing press and had access to the dark room.) 

The light falls on a sheet of paper taped to the near side of the box. 

The image is very faint, but near the middle is the dented sun if you can make it out.  It would be better to fasten black felt around the sides of the box to block out interfering light and make it more like a camera obscura.