If a Star Shines but no one Sees it, is there light?

Just as with the age-old question “if a tree falls in the forest, but there is no one there to hear it, does it make a sound?”, the answer is it depends.

It depends on how you define sound… or light.

One definition requires a receiving component for the air compressions (such as ears) or electromagnetic signal (such as eyes). Without receivers, then by that definition, there is no sound, or light. But that definition comes up short. Why? Just because receiving devices aren’t there to, well, receive, doesn’t mean the emitted compression waves or electromagnetic signals don’t exist. They do exist. This conversation could devolve into a philosophic discussion on physics and existence. There are schools of thought proposing existence depends on our experience, that is, things only exist when we experience them. I’m not touching that.

We’ll concentrate on the light question. Trust me, it exists whether or not someone or something is there to detect it.

Human eyes are wonderful receptors for what we need to identify and understand on Earth. Our eye’s color receptors are called cones, and they seem preferential to the color green.  Also, cones are not sensitive enough to see color well in low light, well, except green in some cases. If you look at the visible light portion of the electromagnetic spectrum using a prism, green is tucked between yellow and blue.  It’s there but surrounded by strong primary colors. Look at digital camera sensors. Two green for each red and blue pixel. The common explanation is that our eyes are more sensitive to green. That does not compute for me. If our eyes are more sensitive to green, sensors would not need more green pixels. It has more to do with how pixels and pixel filters handle white light. Green seems to need a boost. That points to the crux of the green issue.

There are no green stars, and green appears to be lacking in astrophotos, except maybe for bright planetary nebulae.  It’s not that green isn’t there. There’s plenty of oxygen to produce green after those gas molecules are excited by stellar radiation. it’s simply overwhelmed by the way more abundant red from hydrogen.

The universe around us is also chock full of light we cannot see. That’s OK, if we could easily see infrared, or ultraviolet, the rest of our visual experience would be way different.

Back here on Earth, where our visual capabilities evolved, our eyes revel in the visual spectrum, from red to violet. Green is everywhere, thanks to plants. Most plants reflect green light, as a protective mechanism to allow the most efficient photosynthesis.

Digital is great, but I miss my Kodachrome.

What’s in the Sky?

September 11; before sunrise; east:  See a waning crescent Moon and Venus grace the sky, For extra fun you will need binoculars. Open star cluster M44 (the beehive cluster, aka Praesepe, Latin for manger) lies just a bit to the upper right of the Moon.