When the earliest astronomers and philosophers looked up at the night sky, they never could have imagined a sight like this.
What if I told you there are only four single stars in this image?
That’s right. Four.
The rest are whole galaxies, full of billions of stars.
You can tell the foreground stars from the galaxies by the diffraction spikes–astronomer speak for those four bright spikes of light. Can you find them?
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How big is our galaxy, anyway?
And more than that–how do we know?
Consider that we can’t really take a photo like this of our galaxy. We’re inside it, and space travel has not advanced to the point where we can leave it just yet. There’s no way we can get a camera out to take a picture from this perspective.
Most things in the universe–like stars, planets, and even other galaxies–can be measured using their angular diameters. That is, we use trigonometry to find their actual sizes based on how large they appear to us in the sky.
But that doesn’t work for an object that we’re inside of.
In order measure the size of our own galaxy, early astronomers had to get a bit creative–with variable stars.
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Ever seen this before?
It’s not a sight that most of the developed world gets to see–at least not all the time. Light pollution from major cities completely obscures this view. Even in the suburbs where I live, I can kind of make it out–because I know where to look and what to expect.
The best way to really see it is to head out into the desert. Or the open ocean. Really, any place that’s a bit geographically removed from civilization. Growing up, Joshua Tree National Park was always my go-to for dark skies.
Even on an exceptionally dark night, though, you won’t necessarily see this. You’ll definitely be wowed by the vast, bright sprinkling of stars overhead, more than you ever see under less than ideal conditions. But the image above was taken with a long exposure.
That is, the camera shutter remained open for a while to collect more light for one image than your eyes ever will. You and I pretty much only see one image per moment.
So what is this gorgeous, hazy band, anyway?
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Science at Your Doorstep 