Rockhounds

How do people find asteroids now?  I mean, other than by having one detonate over your city, or extinguish your species?

As far as I can tell, the methods used today are identical in spirit to what was done in the days of photographic plates, except that digital cameras and computers make all the steps a lot easier and less expensive.


The first method is blinking.  You take several exposures, pausing for some time after each one, and then play them all like a movie.  All the stars stay still because the telescope is following their motion.  But if you are lucky enough to have a sufficiently bright asteroid in the field of view, it will show up as a little moving dot. 

A related method is to take just three exposures, using first a red filter, then green, then blue.  Combine all three to make a color image.  The stars will appear white (more or less) while anything moving will appear as a sequence of three dots: red, green, and blue.

Finally, you could just take an exposure long enough that the asteroid makes a nice streak. 

The streak method usually happens by accident, while someone is taking a long exposure for other purposes.  It's not a great way to find new asteroids because:

• An asteroid has to be pretty bright to leave a beautiful streak like the one I have simulated here.
• You can't tell which way it was moving.  ( Although you can probably make a high-probability guess. )

I don't want to do any of these things.

What I want to do is use image processing and machine vision techniques to allow us to find streaks that are really, really faint.  So faint that they are right down in the noise.

This will allow us to do two cool things:

• Find rocks that are much fainter than the other methods can.
• Find them several times faster than either of the multi-exposure methods.

The concept is -- compute power is getting exponentially cheaper.  Since I left grad school, compute power has gotten cheaper by a factor of 10,000.  Telescopes have gotten more expensive.  Moreover, compute power is continuing to get cheaper by a factor of two every couple years, while telescopes are continuing to get more expensive.  If we can use compute power to make telescopes more effective at finding asteroids -- that would be a Big Deal.

But to do that, we will need to go to a cold and lonely place.  The dark between the stars.

First Light

A few nights ago it was cool and clear in Mayhill, New Mexico, and I got my first image of a special part of the sky: a place just above the two back stars in the cup of the Big Dipper: Phecda and Megrez.

It's a special part of the sky because there's a little area in which there are no 'local' stars at all.  No stars from our galaxy. It's the place where the Hubble pointed when it took the exposures that were put together to make the Hubble Deep Field image, almost twenty years ago.

My exposure lasted 600 seconds.  Here it is, though greatly reduced for your viewing convenience.

I have also greatly messed with the image's grayscale curve, so that you can see more stars in it.  The original is 16 bits deep -- each pixel is a number between 0 and 65535 -- which your monitor cannot display and your eyes cannot discern.

Now let's zoom in by a factor of two on the center....

Please bear in mind that the Hubble exposure lasted over 100 hours -- about 600 times longer than mine, and its mirror has 23 times the light-collecting area that my beloved T11 has, and, oh just by the way, that it's above the freaking atmosphere! 
So my picture won't look like theirs.

But it's mine.


So...now let's zoom in by one more factor of two.

And here is your window.

The stars that are linked with the pretty cyan lines are local.  Everything else inside that box, all of those dim lights, are distant galaxies.


Wanna take a ride?