It is currently wonderful to be out at night in much of the Northern Hemisphere and there is much to appreciate. Here is a some fun you can have exploring your own night vision
When you try to see in near darkness, any bright light will destroy your night vision for awhile and you have to wait in a dark area for it to recover. This is why sailors wore eye patches when cannons became an important weapon - they could keep one eye dark adapted above deck and would remove the patch in the dim light below. This turned out to be much safer than lighting a match to find the powder bag-) I sometimes wear an eye patch around home when I'm going to be observing outside after dark. It allows me to work in low light conditions without using a light - an old habit I picked up from my amateur astronomy days as a teenager
Here is the neat stuff. Your eyes sense light through two main photoreceptors - rods and cones. Both contain pigments that require time to chemically regenerate after they have been exposed to light. A bit of light hits a pigment, some chemistry happens and a signal is sent out to the brain. The problem is a lot of light can cause so much chemistry to happen that it takes a while before it is sensitive to light again.
The pigment in the rods is very efficient for very low light levels. They need twenty to thirty minutes to recover after being light saturated (the term is "bleaching") ... . When you go out on a dark night your rods are mostly bleached from bright indoor light and it takes up to that time before your eyes adapt to the darkness
The cones, where your color vision originates, have three pigment variations. Their chemistry is different and they only need eight or nine minutes to recover from bright light.
The photosensitivity of your cones is much less than the rods, so when you are dark adapted, most of your vision is colorless. But before that happens your cones are ready to go and your low light level color vision is at its best. This is the best way to see the color in bright night time stars and planets -- the red of Mars, the yellow of Saturn, the brilliant green and yellow of a double star in Cygnus and the orangish-red of Betelgeuse in Orion (the tip of the upper left arm). As your rods recover the colors fade and, assuming the night sky is clear and dark, hundreds of stars come into view. The effect is dramatic.
It is mostly too bright to do this in cites and suburbia, but try it when you are in a dark spot. If you try it with an eye patch to check out the differences between a dark adapted eye and one that is still adapting perhaps you can make people wonder if you're a pirate.
This may seen removed from technology and business, but our connection to machines and other people is often mediated by interfaces. How we perceive and interact with them is a subset of the overall user experience and failure to get it right can cause serious dissonances. Engineering often amounts to a best effort to optimize a complex set of requirements but all too frequently some of these human factors are not known by those charged with creating the software and machines. And, of course, this extends beyond interfaces.
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Speaking of the night sky, the Perseid meteor shower is almost on us. The normal peak falls on August 12, but this year the moon will wash out all but the brightest meteors. You can still enjoy it as the shower builds up over several days. In early August the sky will be moon-free from midnight to dawn with the moon eroding that window as time moves on. The best time may be the few hours before dawn on August 8 through 10, but even if the shower is not as nice as it sometimes is, it is still an excellent excuse to lay out on your back watching the night sky on a warm Summer evening.
I can't wait to get out to the countryside to try this and see if I can see more of the colors in the sky:-)
Posted by: jheri | 08/03/2011 at 08:32 AM