Are you ready for some spectacular sky scenery tonight? Then keep your fingers crossed for clear weather as the slender crescent Moon, Venus and Jupiter provide one of the finest sky shows we’ve seen all year – a conjunction in the west to dazzle the eye and boggle the brain! But just exactly why does seeing bright planets draw together command our attention? Step inside and let’s find out…
“Your eye is like a digital camera,” explains Dr. Stuart Hiroyasu, O.D., of Bishop, California. “There’s a lens in front to focus the light, and a photo-array behind the lens to capture the image. The photo-array in your eye is called the retina. It’s made of rods and cones, the fleshy organic equivalent of electronic pixels.” Near the center of the retina lies the fovea, a patch of tissue 1.5 millimeters wide where cones are extra-densely packed. “Whatever you see with the fovea, you see in high-definition,” he says. The fovea is critical to reading, driving, watching television. The fovea has the brain’s attention. The field of view of the fovea is only about five degrees wide.” Tonight, Venus, Jupiter and the crescent Moon will all fit together inside that narrow angle, signaling to the brain, “this is worth watching!”
When it comes to our eyes, almost every photoreceptor has one ganglion cell receiving data in the fovea. That means there’s almost no data loss and the absence of blood vessels in the area means almost no loss of light either. There is direct passage to our receptors – an amazing 50% of the visual cortex in the brain! Since the fovea doesn’t have rods, it isn’t sensitive to dim lights. That’s another reason why the conjunctions are more attractive than the surrounding starfields. Astronomers know a lot about the fovea for a good reason: it’s is why we learn to use averted vision. We avoid the fovea when observing very dim objects in the eyepiece.
Let’s pretend we’re a photoreceptor. If a light were to strike us, we’d be “on” – recording away. If we were a ganglion cell, the light really wouldn’t do much of anything. However, the biological recorder would have responded to a pinpoint of light, a ring of light, or a light with a dark edge to it. Why? Light in general just simply doesn’t excite the ganglion, but it does wake up the neighbor cells. A small spot of light makes the ganglion go crazy, but the neighbors don’t pay much attention. However, a ring of light makes the neighbors go nuts and the ganglion turns off. It’s all a very complicated response to a simple scene, but still fun to understand why we are compelled to look!
Many of us have been watching the spectacle draw closer over the last several days. How many of you have seen the Venus and Jupiter pair appear one over the top of each other – looking almost like a distant tower with bright lights? What we’ve been observing is Kepler’s Laws of Planetary Motion in action – and it’s a great way to familiarize yourself with celestial mechanics. What’s happening tonight is called a conjunction. This is a term used in positional astronomy which means two (or more) celestial bodies appear near one another in the sky. Sometimes the event is also called an appulse.
No matter what you call it, what you’ll see tonight is a worldwide happening and will look hauntingly like a “happy face” painted on the early evening sky. Don’t miss it!
Our deepest appreciation goes to Shevill Mathers for his dedication in getting this shot to share with us, and all the rest of the great astrophotographers at Northern Galactic and Southern Galactic who have also gave it their best shot! There can be only one…
Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter’s Gold Status.
(Tammy passed away in early 2015… she will be missed)