Dr. Katherine Volk

They also have large parallax motion because they're relatively close to the Earth because we are in the inner solar system.

They're also brighter, so that's the third factor here.

We're seeing these things in reflected sunlight, so the light has to go from the sun to the asteroid or the Kuiper belt object, reflect off and come back to us on Earth.

So this all factors into things in the inner solar system being pretty bright, and bright enough to have been discovered quite a long time ago on photographic plates.

So this is a plot showing the number of asteroids discovered over time.

So the first asteroid here was Ceres in 1801.

And it's not a very fast rate of discovery, but in the 1850s, they must have started surveying more, taking more photographs.

And it really starts to ramp up.

So there are plenty of things.

We're getting up to 1,000 asteroids, well over 1,000 asteroids discovered in the era of just searching by photographic plates.

And that's because they're reasonably bright.

Because the way you had to find these things was using this device called a blink comparator, which is like a torture device in my mind.

That sounds awful.

So you set the photographic plate with the light sources behind them in these two places.

You look through here and you blink back and forth, blanking out one image in the next and trying to spot the difference to see the thing that moved.

So you can imagine that only works for pretty bright things.

Also photographic plates can only image things that are reasonably bright because they're not as sensitive as the CCDs that we have now.

But they did quite well with asteroids.

But of course here in the 90s, you just see this is a log scale.

The number of asteroid discoveries, of course, does shoot up when we get into the digital era, and we get into things like the computer helping us out by spotting the difference so that you don't have to sit at this.