Sunday, December 25, 2011

Big Dipper and Little Dipper (July 4, 2009)

Current mood: pugnacious

This qualifies as nightlife, I suppose.

From where I live, I have no problem seeing the North Star and the Big Dipper. For those whose knowledge of astronomy is limited, the sky rotates around the North Star, also known as Polaris. No matter what time of night (or daytime, if you could see it) or what season of the year, Polaris is going to be in exactly the same spot. Everything else moves through the sky; Polaris is always right in that same spot. Where you are relative to the equator and North Pole determines how far up in the sky that is, but it's always due north.

The Big Dipper, more formally called Ursa Major, is a constellation of seven bright stars, four of them a rectangular cup, three of them a curved handle on that cup. In the evening in the summertime, they're higher in the sky than Polaris, but unless you live in a shopping mall parking lot or the center of a major city, if you can see any stars at all overhead, you can probably pick out most of these.

The Little Dipper, or Ursa Minor, is a lot tougher. It's almost the same shape as the Big Dipper, but faces the opposite direction. Polaris is the last star of the handle. The cup of the Big Dipper (whose top is a bit wider than its bottom) points directly at the rest of the stars of the Little Dipper.

Here's a page showing the two constellations together. Hover over the picture to see the constellations. Move the mouse off to see what you'd see overhead in a dark enough sky.

From my spot on the planet, I can only see Polaris, and one star of Ursa Minor's cup. The reason: light pollution. Artificial light from human activity brightens the background darkness of the sky, making it difficult to impossible to see dim stars. The brighter the background, the more stars disappear.

Polaris is a +2 magnitude star. The brighter the star, the lower the number. Most of the Big Dipper's stars are also about +2. Right next to the first star on its handle is a +4 star, much dimmer. Most of Ursa Minor's stars are about +4 or even +5. Given a dark enough sky, you might be able to see it. But if you can't see that tiny one next to that first Ursa Major handle star, you won't see five of Ursa Minor's seven.

The solution is not simple. If the power were to go off on a regional basis, and the sky was otherwise clear, every one of those stars would instantly become visible. Everyone needs to think differently about outdoor lighting. Your porch light, your yard light, the light on the side of your building -- if any of them shine light sideways or up, they are contributing to light pollution. That is the majority of outdoor lights, nearly every one of them on private property, and those that aren't are mass-installed by a governmental body -- city street lights, or a state department of transportation, for example.

Many are ornamental, serving no function other than to change the nighttime looks of something. Many are there for "security". Many are there for a commercial purpose. A few light up flags or the side of a building. Getting these changed, or turned off, requires a bulb-by-bulb, property-by-property discussion. Almost insurmountable. But not impossible. Knowledge is key.

Prior to 1890, everyone could see 14,000 stars in the sky. Today, if you can see 500, count yourself lucky. If you are religious, you are missing God's majesty. If your beliefs take you elsewhere, you're still missing a grand show. Regardless, it is mankind's doing that is undoing that show. Your and your neighbors' money, or your tax money, is paying not to see that show. Think differently, and pass the word around.

1 comment:

GLBLAKELY1974 said...

i enjoyed reading this blog. It makes sense. Also, i'm enrolled in astronomy. I can't wait to learn all about this and find out what stars and planets and constellations i can see in chicago.