the sky's not so big after all

What's Really Visible at Night

There are roughly 300 billion stars in the Milky Way, but only 2,500 stars are available to the unaided eye in ideal conditions from a single spot at a given time. Light pollution in cities and suburbs throttles the number down dramatically: in New York, as few as two dozen stars are visible.

Almost all of the sky objects visible to the naked eye are stars that reside in our galaxy. The bulk of those you can see are relatively nearby, within a few thousand light-years. Most are actually within a few hundred light-years. For comparison, the Sun is about 26,000 light-years from the galactic center; the galaxy itself is about 100,000 light-years wide.


4 Responses:

  1. adameros says:

    I can't help but wonder how much the street lights in San Jose and the neighboring communities cost.

    They use special lights that reduce the light pollution dramatically so Lick Observatory can still operate. In fact, it's such a successful program that Lick Observatory named one of the asteroids it discovered after San Jose as a means of thanks.

  2. kingfox says:

    Growing up spitting distance from their worst case scenario, it's a condition I've grown up with. Any time I've visited family out west in the middle of nowhere, it's just dumbfounded me what's visible.

    One crackpot teacher I had in high school tried to organize people year after year to write politicians about the problem of light pollution. He cited lights along highways that pointed at a ninety degree angle to the road, so half of the light was being sent upwards, and parking lots with lights point both up and down.

    Every time I watch the episode of the Simpsons where Lisa turns the lights down, I picture him ranting about being an astronomer in New Jersey.

  3. vxo says:

    In the suburban hell surrounding Miami, the light pollution is pretty bad, thanks to county ordinances requiring that most streets have the holy fuck lighted out of them with the cheapest possible lights.

    I read a thing long ago that described the good and bad types of lights, with regard to light pollution. The ones that have the lens pointed downwards underneath a sort of paw-shaped metal hood are the best; the worst are the el cheapo sodium and mercury vapor lights that are sold to annoying people at Home Depot as 'security lights', and the spherical glass globe lights.

    I was quite amazed when I went out and walked down a road in the Everglades in the middle of the night by starlight... I had forgotten that was possible, since the noise floor of vision is pushed so high.

  4. I live many miles from big cities, but sometimes I can see orange light from Bakersfield and LA, is most of that light from street lights? If it is it seems like a lot of money could be saved by phasing in dimmer lights that redirect more light toward the ground.