Wednesday, February 23, 2011

Venus, Moon and Morning Coffee...

Written by Tammy Plotner

If you’re an early riser, then perhaps you’ve noticed Kepler’s Laws in action? No, it’s not a new Bruce Willis movie, just the inevitable pairing of the waning crescent Moon and shining Venus. As you can see from this great photo taken last month by John Chumack, it happens as regular as clockwork… and it’s about to happen again. But what is it about such pairings that command our attention? Let's find out...

According to the Sky & Telescope press release, the brightest planet and the eerie waning crescent Moon will create an arresting sky scene low in the southeast in the early dawn of Monday, February 28th, and Tuesday, March 1st. “These are the two brightest astronomical objects in the sky after the Sun,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “They’ll certainly catch your eye, if you look low in the southeast about 60 to 40 minutes before sunrise — weather permitting.”

Venus will be shining to the Moon’s lower left on the morning of Monday Feb. 28th. The next morning Venus will be to the Moon’s right or upper right. Although they look close together, they’re not. Venus is currently 400 times farther away than the Moon. It’s at a distance of 8.8 light-minutes (the distance light takes to travel that far), compared to the Moon’s distance of 1.3 light-seconds. In miles, that’s 99 million miles for Venus and just 249,000 miles for the Moon. (In fact, you may have driven cars enough miles to get to the Moon.) And despite appearances, Venus is 3½ times wider than the Moon’s diameter.

“Why do people care about this?” asks MacRobert. “Because some people know we need to look up beyond our own little world — and recognize where we are as part of nature, part of the universe. So many of us live our busy little ant-hill lives without ever noticing the gigantic universe beyond the anthill. A lot of people don’t even know you can see alien planets from your driveway while you’re unlocking the car to go to work.”

But just what is it about such a celestial scene that draws our eye like no other? 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.

“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 and even watching television. The fovea has the brain’s attention. The field of view of the fovea is only about five degrees wide.” When Venus and the crescent Moon are close to that narrow angle, it signals to the brain, “this is worth watching!”

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 (as does hooting and screaming while pointing at the morning sky). A small spot of light makes the ganglion go crazy, but the neighbors don’t pay much attention (unless you’re in your pajamas cleaning the snow off your car). However, a ring of light makes the neighbors go nuts (and their dogs) 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!

And perhaps howl just once.

Many thanks to John Chumack of Galactic Images and to Sky & Telescope Magazine for the heads up!

No comments:

Post a Comment