Click here for a higher-resolution image
As you can see from other images in this gallery, it is not uncommon in a long-exposure image of an astronomical object to catch a few, or even more than a few, asteroids passing through the frame. We thought it would be interesting to see how many asteroids we could get if we deliberately tried to capture as many as possible. As a first step, we picked a night, and time, a week or so in the future and used the JPL "SB What's Observable" tool to get a list of all small bodies (asteroids and/or comets) that would be visible. We wrote a small computer program to plot all the asteroids over an all-sky map, as a nice way of picturing where the largest concentrations of asteroids would be. Here is that image:
Although you can't read the constellation names, you can see that the densest area for asteroids on this particular date and time was in Virgo in the area a bit north of Spica. This is precisely the area of sky satisfying two simultaneous conditions: it is close to the Ecliptic (the sine-wave like curve plotted on the map), which is where most asteroids live, AND it has a Right Ascension that's in opposition to the Sun for my given date and time. Just like the outer planets are brightest near opposition, since then they are closest to Earth, so too are the asteroids. Being (a) on the Ecliptic and (b) at opposition maximizes the chance of catching a lot of asteroid, as the map shows very clearly.
Now, we could have just picked an area around the word "Virgo" on the map and would have probably had good success. But we went a step further, and had our program search all 2x1-degree fields in the area (the size photo we planned to take) and count the number of asteroids PLUS the number of NGC galaxies. Since this is galaxy-rich area we thought it would be interesting to have many asteroids AND lots of galaxies, with at least a few largish NGC galaxies. So using this we chose a particular field of view which was predicted to contain about 55 asteroids and five NGC galaxies (4731, 4731A, 4775, 4786, and 4813).
We took just seven five-minute L exposures, and due to a problem with the 4th image we discarded it. So the asteroid trails look like two dashes close to each other, one dash from images 1,2,3, then a small gap from missing image 4, then a dash for 5,6,7. (The asteroid trails are colorized green for easier visibility.) The asteroid names are shown in green, but note that neither the names nor dashes are very visible in the image above, or even in the high-resolution image linked to above, because their resolution is too small. Click here for an even higher-resolution image in which all the labels are nicely readable. In this largest image, besides the 55 asteroids we have also annotated about 1100 galaxies that are visible in the frame. Labels are always just to the right of the objects they label. Next to each asteroid trail, the name of the asteroid is shown followed by its magnitude. For galaxies the galaxy name is followed by its magnitude and its distance in millions of light years (or billion if it ends in a "b"). Galaxies just labeled with a number are those for which a redshift value (from which distance is determined) has not yet been measured. The largest galaxy, at right center, is NGC 4731.