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An independent monthly newspaper serving the community since 1988
  Night Sky
 

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

June 2015 night sky

—Charlie Christmann

Our home

As June begins, our Milky Way galaxy rises in the east at about 9:00 p.m. By August, it is high in the night sky by 9:00 p.m. To see it, get as far away from city lights as possible on a moonless night, and then let your eyes adjust to the darkness for about twenty minutes. Even then, the light is too faint to register any color to our naked or binocular aided eyes. It takes large telescopes and long exposures to get any color.

At first glance, the Milky Way is a dimly glowing swath of the sky. No real stars are directly visible in the glow, just those in the foreground. With your eyes acclimated to the dark, you can begin to see bands of darkness within the glow. Because we on Earth sit within the galaxy, our view of the Milky Way is edge-on.

Within the constellation Sagittarius lies the galactic center and the black hole that resides there called Sagittarius A Star (Sagittarius A*). The dark regions are cold dust and gas clouds obscuring the stars behind it called dark nebulae (plural for nebula). The clouds are relatively thin, but extend for light years. That is enough gas and dust to blot out the background. They also hide our galactic core from visible light telescopes. Most studies of Sagittarius A* have been at infra-red and radio frequencies. Those are more able to penetrate the dust and gas.

The most prominent dark nebula is the Northern Coalsack, located just below and to the right of the bright star Deneb in the constellation Cygnus. Just as there are dark nebulae, there are also bright nebulae. Below Deneb is one of the brightest parts of the northern Milky Way. This bright region is a rich target for binocular observations. If you look from dark skies, you just might make out the California coast in the North American Nebula.

Look higher in the night sky toward Cassiopeia and Perseus. From here you are looking toward the outer edges of the galaxy toward intergalactic space. Somewhere between the outer edge and the ominous black hole within a spiral of arms swirling from the central bulge sits Earth on a lonely offshoot called the Orion-Cygnus spur, 25,000 light years from the center and another 25,000 light years to the rim. Our spur breaks off the Sagittarius Arm and is about ten thousand light years long and 3,500 light years across.

From our location, Earth rotates around the galactic center every 250 million years. The last time we were in this position relative to the galactic spin, dinosaurs were roaming the planet. Since Homo sapiens first evolved on this planet, we have rotated less than one degree around the galaxy.

Astronomer’s current thinking is that it is a good thing we live in a quiet backwater. Close to the central bulge and the black hole is very crowded with other giant stars that, along with the black hole, spew radiation; not a very conducive region for life to form and thrive. Further out, the materials needed to form stars and solid planets gets thinner. Since life as we know it needs a rocky planet, out in the fringes of the galaxy, the chances of forming a sun-like star with an Earth-like planet gets less likely.

While every star we see in our night sky lives within our own galaxy, we can see other galaxies outside of our home galaxy. If we lived in the southern hemisphere, we could see our nemesis, Andromeda, a huge spiral galaxy, as a smudge of light in a dark night sky. Andromeda is on a collision course with us. In about four billion years, the two galaxies will meet, their stars will begin to intermingle, eventually merging into a new monstrous elliptical galaxy. The fate of our solar system is unknown; we could be flung into the center of the new galaxy with deadly consequence, or exiled into intergalactic space, thrown out of the galaxy as a lone wandering star system as the combined gravity reforms and reshapes the combined galaxies.

Either way, new evidence indicates our two galaxies may already be interacting. Andromeda contains a halo of gas extending out about two million light years. Though we cannot see it from our vantage point, it is assumed we also have such a halo around our galaxy. With only 2.5 million light years between us and the edge of Andromeda, our galaxies are most likely already touching.

Be a good neighbor • Keep the stars visible for everyone • Turn off your outside lights at night

Summer brings the spectacular night sky vista called the Milky Way into view, but only under dark, clear skies. Unfortunately, city lights and urban sprawl are spoiling this wonder of our night sky. Most people today have never actually seen our home galaxy with their own eyes in all of its natural glory; they cannot get far enough away from the city light. Even here, in semi-rural Placitas, where I live, the lights of Rio Rancho, Albuquerque, Bernalillo, and the San Felipe Casino cast a glow into the sky, blotting out all stars dimmer than about third magnitude. Our eyes are capable of seeing sixth magnitude stars with no light pollution.

All of that light shining into the sky reflects off dust, pollution, and clouds in the atmosphere, reflecting some of it back to the ground making the sky appear brighter. And just like at dusk and dawn, the lighter the sky, the fewer stars you can see. We know where the dust and pollution comes from, but high flying aircraft also contribute to the clouds. Vapor trails are clouds. They spread out thin enough eventually that they are not visible, but leave behind a thin veil of ice. The sum total, however, of many planes add up to a thin haze of clouds that also obscures and reflects. This all adds up to a loss of access to the night sky.

And now, it seems, more and more residents are turning on, and leaving on all night, their outside lights; many are installing improperly shielded or flood lights, contributing to the loss of the natural treasure that is our night sky. What a shame. Let’s keep our stars. Turn off your outside lights at night. Or at least, shield them properly, downward.

 
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